Tube-Town Forum
Technik => Tech-Talk TT-Projekte => Thema gestartet von: Pringles1 am 26.04.2020 20:56
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Hallo an alle
Letzte Nacht habe ich den BFlex Amp fertiggestellt. Ich habe es wirklich genossen.
Ich habe ein Problem bei den Messungen festgestellt, aber mein Deutsch ist sehr schlecht (Google Übersetzer). Ich werde versuchen, Ihnen von dem Problem zu erzählen, um zu sehen, ob Sie mir helfen können, die Lösung zu finden.
Heute Morgen habe ich die Ventile aufgesetzt und angefangen, Messungen durchzuführen, ein wenig Hochspannung und besonders auf der Leistungsstufe. Ich lege die Maße bei. Auch wenn angeschlossen, hören Sie ein Summen im Ton, das abnimmt, wenn ich das Tonpotentiometer berühre. Auch die Lautstärke des Verstärkers ist nicht hoch. Ich habe die Schaltung, die Komponenten und ihre Polarität dreimal überprüft und bin auf keine Build-Probleme gestoßen. Was halten Sie von den Maßnahmen? Können Sie mich dahin führen, wo ich darauf bestehen muss, nach dem Problem zu suchen?
V1 12AX7 (V)
1 - 232
2 - 0
3 - 2
4 - 46
5 - 46
6 - 221
7 - 0
8 - 2
9 - 46
V2 12AX7 (V)
1 - 283
2 - 0
3 - 2
4 - 46
5 - 46
6 - 263
7 - 0
8 - 2
9 - 46
V3 6V6GT (V)
1 - 0
2 - 46
3 - 466
4 - 468
5 - 45
6 - 468
7 - 46
8 - 0
V4 6V6GT (V)
1 - 0
2 - 46
3 - 469
4 - 469
5 - 45
6 - 468
7 - 46
8 - 0
B1 point - 468 V
B2 point - 465 V
B3 point - 402 V
B4 point - 386 V
AC at home- 263 V
Vielen Dank für Ihre Zeit und Ihre Hilfe. Anbei auch Fotos von der Konstruktion.
Jaime (Spain)
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Hi,
I'll try in english, I hope that's better for you than german.
I haven't built the amp, I will try according to the schematic, your measurements and pictures.
if your wall voltage at home is really 263V AC, this is really high. The circuit is designed for 230V.
Given a wall voltage of 230V, the power transformer transforms the voltage (under load) to 300V. So the transformation factor is roughly 1,3
If your wall voltage is 263V, then the secondary voltage of the power transformer is supposed to be around 340V AC. Please measure the actual value in your amp.
After rectification this yields a B1 of 450VDC which is not far from your measurement. With too high voltages everywhere, the operating points of all tubes are different than in the design.
Pin 3 of the power tube is the anodes, Pin 4 the screens. The voltage on the screens is supposed to be smaller than the anode voltage. This is not plausible with your measurements, where the screen voltage is higher than the anode voltage. Double check if you miswired B1-->Center Tap of the output transformer / B2 --> Screens. If so, you are connecting the output transformer primary winding to the small screens who will not like this and the function principle of the power tube is compromised. This would explain the low power/volume.
Bias: you measure a positive voltage of 45V here (Pin5 on the power tube). This value is supposed to be negative. You might have reversed your measuring probes. If so, -45 is still not plausible for a 6V6 tube. The schematic does not tell the Bias voltage but I would expect something around -30V. If you really have -45V the operating point of the tube is too cold which could also explain the low volume. Double ckeck the bias voltage. Ckeck, if it changes when you turn the bias pot/trimmer.
There must be a measuring or wiring error in the heaters. 46V on pins 4-5/9 (Triodes) and 2/7 (Power tubes) is not at all plausible. Are you sure, you set your multimeter to AC when measuring the heaters and you read V not mV? 46V DC can occur, when the design has an elevated heater (and AC is still 6,3V), but the schematic of the BFlex has none. So your heater wires should read 3,2V AC to ground or 6,3V AC between each other (or a fair amount above it due to your high wall voltage). Double check this.
Part of the heater winding is the center tap (Black). Is it connected to ground?
Hum can have multiple sources. The usual suspects is mistakes in the wiring of the heaters, miswired or bad filter caps in the power supply of the high tension (wrong polarity, missing ground connection), coupling between conductors (lead dress, parallel wires where they shouldn't be, twisted wires that shouldn' be twisted together).
What frequency does the hum have? 50Hz is mostly a heater problem, 100Hz ist mostly a power supply problem in the HT.
Did you check, where the hum occurs? In the preamp or the power amp or both?
pull V1: if the hum is still there, it is a problem after the preamp. Pull V2: if the hum is still there, it is a problem in the power Amp after the phase inverter. pull v1 and v2: If the hum goes away, insert v2 again. If the hum returns, it is a problem in the PI
turn down the "Blast" control. If the hum goes away, it is a problem of the first gain stage. If it stays the same, the problem is after it.
In rare occasions one of the tubes is bad.
But according to some of your odd measurements I would start troubleshooting elsewhere.
Hope that helps.
BR
Robert
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another question:
What is your quiescent current in each power tube and how do you measure it? There is no measuring resistor in the schematic.
BR
Robert
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Hi jamie,
263V at the wall?
Do you have a fresh battery in your multimeter?
regards
Jochen
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hi,
Danke chaccmgr and cca88 für deine schnelle Antwort. Ich kann es mit Google Übersetzer ins Deutsche übersetzen, obwohl es für mich auf Englisch leichter zu verstehen ist. Danke für die Mühe.
Die Messungen haben Recht, sie sind negativ (das Kopieren und Einfügen ist böse). Was die Wechselstrommessungen in meinem Haus betrifft, denke ich, dass es ein Problem mit dem Multimeter geben muss, da es weiterhin hohe Spannungen anzeigt, was nicht normal ist. Ich habe den Trimpot von der Vorspannung auf -32 V an Pin5 entfernt und die restlichen Messungen bleiben ähnlich (obwohl sie um etwa 20 V gefallen sind. Ich habe die Verdrahtung des OT-Transformators überprüft und theoretisch sind sie gut verdrahtet
B1 (CT 444Volt) und B2 sowie hohe Messungen an Pin 3 und 4 der Leistungsventile folgen. Ich werde ein weiteres Multimeter kaufen und wenn es ankommt, wiederhole ich die Messungen.
Thanks chaccmgr and cca88 for your quick response. I can translate it into German with google translate for your convenience, although for me in English it is easier to understand. Thanks for the effort.
As for the measurements, you are right they are negative (the copy-paste is evil). As for the AC measurements at my house I think there must be a problem with the multimeter because it keeps reading high voltages which is not normal. I have removed the trimpot from the bias down to -32V on pin5 and the rest of the measurements remain similar (although they have dropped by about 20 v. I have checked the wiring of the OT transformer and in theory they are well wired to
B1 (CT 444Volt) and B2, and high measurements on pin 3 and 4 of the power valves follow. I am going to buy another multimeter and when it arrives I repeat the measurements.
I write the news measurements_
V1 12AX7 (V)
1 - 220
2 - 0
3 - 2
4 - (-32)
5 - (-32)
6 - 210
7 - 0
8 - 2
9 - (-32)
V2 12AX7 (V)
1 - 270
2 - 0
3 - 2
4 - (-32)
5 - (-32)
6 - 250
7 - 0
8 - 2
9 - (-32)
V3 6V6GT (V)
1 - 0
2 - (-32)
3 - 442
4 - 438
5 - (-31)
6 - 441
7 - (-32)
8 - 0
V4 6V6GT (V)
1 - 0
2 - (-32)
3 - 442
4 - 437
5 - (-31)
6 - 400
7 - (-32)
8 - 0
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Hi,
i assume you are still measuring the heater in a wrong way. It should be either 3.3V or 6.3V AC depending if you measure it to ground (CT) or between the two windings. Make sure your DMM is on AC for this measurement. Please check first at the transformer and then on the relevant pins at the valve e.g. pins 4,5 and 9 on your 12ax7.
(-32) is strange for the heaters.
Gerhard
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Yes! you are right!!
3.2 V AC at Pin 2 and 7 in V3-V4 (CT ground) .
3.2V at Pin 4,5 and 9 of V1-V2 (CT ground) .
Sorry for my ignorance and thanks for your patience!
Jaime
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Jamie,
anyway - be always sure to have a fresh battery in your multimeter - with worn batteries, most of them tend to have very high voltage readings when the battery is low...
Just do it - it does not take much effort an expense ;)
regards
Jochen
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Thanks everyone for your help.
Finally I have changed the battery of the polymer and I have made all the measurements again (this is sooo much more difficult than building it, hehehe).
The Hummm has decreased but the amp is still low volume.
AC at home: 222V
V1 12AX7 (V)
1 - 189
2 - 0
3 - 2
4 - 2,7 (AC)
5 - 2,7 (AC)
6 - 180
7 - 0
8 - 2
9 - 2,7 (AC)
V2 12AX7 (V)
1 - 232
2 - 0
3 - 2
4 - 2,7 (AC)
5 - 2,7 (AC)
6 - 215
7 - 0
8 - 2
9 - 2,7 (AC)
V3 6V6GT (V)
1 - 0
2 - 2,7 (AC)
3 - 379
4 - 376
5 - (-33)
6 - 378
7 - 2.7 (AC)
8 - 0
V4 6V6GT (V)
1 - 0
2 - 2,7 (AC)
3 - 378
4 - 376
5 - (-33)
6 - 378
7 - 2.7 (AC)
8 - 0
B1 379 V
B2 378 V
B3 330 V
B4 320 V
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Hi,
as your dc voltages seem to be fine, focus on the ac path.
You might want to check for missing ground or under-board connections - e.g. the ground connection at R11/R12.
Btw.: the picture shows only 2 resistors at the terminal next to V1. Is the third missing or just hidden behind the cap?
Best, Peter
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Hi,
before we start any guesswork, you should try to identify, where the problem is. Somewhere in the signal chain you lose signal.
You did not measure voltages with a signal applied. Try to get hold of a signal generator and apply a sine wave signal of about 50mV to the input (a typical bass output with a passive bass). TrueRTA is a free software that can be used.
Best measurement is with a scope (you see if the output waveform is the same as the input or if it is distorted) if you have access to one or somebody who knows how to operate it, use it.
But you can get ballpark figures with a multimeter too.
measure the AC input to the first preamp tube and measure the AC output at the anode. The amplification factor is supposed to be somewhere in the region of 40 to 65 times (depending on the actual component values at the tube). Don't forget to measure your blast pot, if there are any unwanted losses. If your pot is a log pot and the control is set to 12 o clock, you should measure roughly 10% of the input signal at the output. If not, check your wiring.
If you measure both preamp-tubes fine, the problem is in the power amp.
The phase inverter is supposed to amplify by a factor of roughly half of the normal amplification. Look up in the 6V6 datasheet, what voltage swing the power tubes require for full output. The preamp + PI must be capable of delivering this required output voltage. if you measure this fine too, your output tubes have a problem.
My guess is, that the operating point of the output tubes is not correct. To find out, you must measure the quiescent current. This gives you a feeling of the operating point of the tubes. If it is not correct, the volume is low and the tone can be lifeless and or distorted. The operating point is set using the bias trimmer. The more negative the bias voltage is, the "colder" is the am biased and vice versa. With a too cold bias the amplitude of the output tubes is too small which equals to low volume. There can also occur crossover distortion with too cold bias (to be seen on a scope).
Too hot is not good either, your anodes virtually get too hot and get destroyed.
As the kit does not have measuring resistors on the cathode, you must measure it the hard way. Warning: you must take two measurements under full voltage!
- switch the amp off and discharge all capacitors
- measure the DC resistance of each primary winding of the output transformer (CT to anode1, CT to anode 2). Maybe you must unsolder the leads to get correct values. The reading should be almost the same for both halves.
- reconnect the anodes, turn the amp on without a signal applied
- measure the voltage drop across each primary winding
- use Ohm's law to calculate the current: I = V/R. The target value is given in the schematic. If the current without signal is too low, make the bias less negative. Is it too high, make it more negative.
If all this does not lead to success, then there is another error somewhere (wiring, component value). I once built an amp and confused two resistors, one with 470R and another with 470k. it took a while to find the error, it was corrected in 2 Minutes and the amp works fine since.
Good Luck
Robert
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Hi,
When I finished wiring an amp I do the following steps to test:
1. Static test with the amp disconnected
- check that the power and output transformers are wired correctly
- measure DC resistance from each cathode to ground
- measure DC resistance from the rectifier to the last preamp node. The meter should read the combined resistances of all resistors in the power supply plus the resistance of the choke (if the amp uses one)
- measure DC resistance from each plate across the plate resistor
- trace the signal path and measure both for continuity and the correct resistance to ground - I also check whether this varies if I turn the controls
Usually I identify wiring errors at this stage.
2. Live test with voltages applied
Here I test whether the voltages are in the range where they should be. I start with the amp on standby, no power tubes inserted, and check heater voltage and all other secondary AC voltages, and whether the negative DC bias voltage is present at the input of the power tubes first. Next I switch the standby on and measure the DC voltages in the circuit. If everything is fine so far, I insert the power tubes and repeat the procedure.
Anything that got missed in the static tests will usually reveal here. A tough one was a bad preamp tube socket - everything measured fine but there was no voltage on the cathode, due to the fact that the tube pin did not connect to the terminal in the socket. After I replaced the socket the cathode voltage appeared as it should. Another tough one was a miswired output transformer where I confused the center tap with one of the primaries and wondered why I got ugly distortion. Switched the wires and the amp sounded fine (it still does BTW).
This is only a rough description.
Another good way is to take the schematic or layout and colormark every verified connection.
Cheers Stephan
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First of all, thank you for all the comments and helps. I have followed all your advice and I have not detected any
clear problem. I have checked the power transformer and these is the filament 1 # (H1 and H2) desoldered of Pin 2 and Pin 7 of V4 ... Could this be the problem?
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Where is your negative terminal (black cable) attached to? Chassis or GND Terminal?
Heater Voltage seems to be a bit low so if we can exclude a bad negative terminal connection it might be advisable to change the primary side wiring to a slightly lower setting (as per your measurement you are only in 220Vac region) to get HEater Voltage a bit more close to 6.3Vac (3.15V per side).
At all the complete amp looks like it is built in a clean and accurate fashion but it would be great to see more on an overview so we can check visually on how all the grounds hooked up and signal wires routed.
just my 2c
blues
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Thanks, bluesfreak!!
If I understand the question well, the cable is connected to GND. I add more pictures about the build process. I hope it facilitate your assessment.
Best regards,
Jaime
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Hi,
All components do have a tolerance. Capacitors have 10-20%, potentiometers 20% or even more and voltages of course too.
The heater of the tubes is designed for 6,3 V. Let's reduce the 10% tolerance from the 6,3 V and you will get 5,67 V. So your heater voltage is still acceptable.
I also recommend to check the voltage with an other DMM with full bateries. Cheap DMMs and/or empty batteries are a big source for wrong readings.
If the voltage is still to low than use an other primary to "raise" the voltages a little bit.
Best regards, Dirk
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Thanks Dirk and all for yours replies.
I have reassessed all measurements with a professional multimeter, and are the same. The heaters measure 6.06 V (226 V at home). I have done the fifth check of the circuit, the resistances, the capacitors, etc. and again I have not discovered any error (and surely there must be some). I have checked the transformers, the voltages of the PT and the resistances of the OT and they are all correct. I have reviewed all the GND and they have continuity with the chassis. Regardless, I've plugged my bass in the amp, and the volume is still pretty low (I have to turn on full the bass volume and amp volume to have a comfortable volume at home. It still has quite a bit hummm too which decreases a lot when I touch any pot on the amp... Any idea where is the problem? Any help?
Best regards,
Jaime
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when the hum level changes when you touch a pot I would assume that you have a shielding/Ground issue. Maybe a ground loop in a shielded cable (both ends of the shield connected to ground where only one end connected is the right way)
You say, you have continuity from all GND-ponts to the chassis. Do you have continuity from GND to the PE-connection of the amp? Does your house installation have an Earth wire at all? I live in an old house and have these issues in some rooms.
Did you check the amplification in each stage to identify where you lose signal?
Did you measure the output of your bass? Having this number you could calculate the theoretical amplification factor in each stage depending on the other components and voltages and cross check with your measurements.
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Thanks Robert,
I check the shielded cables continuity, and the brigth jack (upper at picture) signal doesn't continuity with GND and the shield yes. But the brown jack (lower at picture) yes... When I put the plug, the brown jack signal doesn't continuity with GND and shield yes.
Is it possible to check the amplification at each stage to identify where I lose the signal without oscilloscope?
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yes
you need a known input signal, say 50mV AC and a multimeter
measure it at the input of the tube (grid1) and note it
measure the signal at the anode and note it
do so at each tube, input signal vs. output signal at each tube
then we can get a feeling, where there might be a problem
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regarding the shields:
the shield is grounded, ok
the question is, if it is connected to GND more than once (on both ends). If yes, you have a ground loop. It must be connected to GND only on one end,
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Yes Robert, it's connect only the end of the jack. The other end is not connected.
I make the measurements and tell you about!
Thanks,
Jaime
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Hi Jaime
Curious what your measurements will say
Regarding the hum:
Hum can have many causes, in most cases it is a grounding or wiring issue
I noticed that your heater wiring is kind of „spacious“. The wires are well twisted but run in very large loops. You could make them much shorter.
On the first tube the heater wires are very close to other pins, one wire even touches the anode cable. The other wire comes to the soldering pin from the inside. Solder it from the outside to get more spacing to Avoid hum coupling
The center tap of the heater secondary is connected to ground?
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Thanks Robert,
Yes, the center tap of the heater secondary is connected to ground. And you are right. I have change to another socket that I know for sure is grounded and now the hummm is down. I'm surprised, because I had tried it before and the humm persisted.
As for the output of the bass is 60mV (AC). When I play with a lot of punch, it's increase around 200-150mV. I have tested bass on another 3 Watt guitar tube amp and it has a volumen sounds similar to the Bflex, so I think it sounds comparatively low (with the same 8 Ohm cone) since BFlex has 18 Watts, right? I have also feel that when I connect the bass to the Brown jack of Bflex the sound is little louder, especially the bass.
Robert, in order to not make mistakes, the signal source has 50mV (AC) but the measurements are as follows? (Excuse my clumsiness but I want to make sure I make some good measurements for you can help me):
preapms: V1 pin 7 to 8 and the pin 2 to 1? Boths in DC or AC? From V2 the same?.
power section: V3 and V4 pin 4 or 5 to pin 3? (AC or DC). And in all the measurements do I put the ground on the chassis?
thanks for your great patience.
Best regards,
Jaime
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hi Jaime
on triodes the input pins are pins 2 and 7
output pins (anodes) are pins 1 and 6
pins 3 and 8 are the cathodes that will not help us
all measurements to ground
so you measure the Input to V1a on pin 2 and the output on pin 1. In this particular circuit the output is supposed to be roughly 35 times the input
same procedure on V1b, but the amplification factor here is supposed to be around 50 to 60 times
V2 is the phase inverter, here it is a paraphase topology. I'm not an expert for paraphase amplification factor but just do the same at this tube and post your results.
then we have a clearer picture and can move on
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Hi,
the brown input is supposed to be louder: the voltage divider between R2 and R30 leaves more signal to V1a. The bright input accentuates the highs, so it is according to the design that the Brown input is more bassy.
an 18W Amp is capable of delivering deafening sound levels in a small room. I can't crank my 15W Madam Guitar Amp with my bass to full volume without getting aching ears. So the expectation for the BFlex is to be loud.
Measurements and calculations:
I double ckecked and found an error re the amplification factors in my last post (calculators can be found e.g. on www.ampbooks.com):
Please set all controls to 12 o clock. All measurements are AC, reference to ground/chassis (you checked continuity from GND to Chassis?)
To measure the amplification factors you need a steady signal. Playing bass and measure will not suffice.
When measuring with a steady signal applied and your load and the speaker output is connected to an actual speaker, this can get quite loud and nerve wrecking. Get a dummy load (high power resistor) of 4/8/16R and connect it to the appropriate jack.
As Dirk mentioned, all components have tolerances so don't expect the theoretical values to be measured. But the ballpark figures must be ok of you have an error in component value or other.
V1a is supposed to amplify 30,6 times (in theory). If you insert a 50mVAC Signal to Pin 2 you should measure 1,53VAC on pin 1. Measure the signal at pin 2 and not at the input of the amp. Measure both and post.
Your Gain Control (Blast) is supposed to be logarithmic. Set to 12 o clock, the output on the middle lug is supposed to be around 10% of the input. Measure both and post.
V1b is supposed to amplify 43,59 times (in theory). Depending on your input signal you can do the math yourself. Measure both and post.
The tone-stack is supposed to attenuate the signal by -21dB (in theory) which equals to 0,089 times the input. Do the math based on your actual signal entering the tone stack, measure both and post.
there is no calculator on ampbooks.com to match the exact topology of this paraphase splitter. Especially R23 is quite a high value with 15k. No clue why that value was chosen. -->Dirk?<--
I suppose, it was chosen to attenuate the signal to prevent the phase-inverter or the power tubes to clip
--> if yes, this might be our point of signal loss
Measure both input and output for each side of the PI and post the values.
Operating Points of the power tubes:
Did you measure the quescent current of your power tubes? This is a crucial information for judging, if your power amp can deliver it's maximum power.
Double check the values of R28/29 if they are really 1k. If they are higher, this will reduce the volume.
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Dear all,and in particular to Robert.
I am deeply impressed how you guide through the different steps of checking a valve amp and doing the appropriate Math. This step by step guidance contributes so much to beginners and helps them (and me) to do it by there own. So pls keep going and many thanks for your time and efforts!
Cheers Gerhard
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:danke:
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Thank you so much Robert!
Of course without your help, wisdom and patience and the other wise men in the forum, it would be impossible for newcomers or novices like me!
I'm not quite sure if I did the measurements right. In V1 I have applied a 84 mV (AC) signal on Pin2 and in P1 the measurement has been 0.000 V (AC) and 192 (DC). I have also applied the signal on P7 and the reading on P6 has been 0.000.
I made a mistake and applied a 2.15V (AC) signal to Pin 2 and the reading to P1 46.4V and when apply to Pin 7, the reading to Pin 6 43.5V The measurement in the middle lug of Blast pot was 1.65V.
Then I applied a 440mV signal on P2 and the reading on P1 was 11.7V. and when applied at P7 (390mV) the reading at P6 was 9.98 V. The Blast pot 0.31.
I have also adjusted the Bias with the new multimeter and when I played the amp to the bass it sounds louder than before, but at full volumen of the bass and amp, the windows don't move ... ???.
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Hi Jaime,
Hard to say from a distance why your measurements are odd and varying.
Feeding 400+ mV will not help as any stage will go into clipping and you read a compressed signal instead of a correct one.
What is the frequency you are feeding? Most multimeters have difficulties reading frequencies below 1kHz
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I use this transistor tester which is also capable of emitting a square wave from 10Hz to 2000kHz. The wave that produced the least voltage was 1000 Hz with a voltage of 2V (AC). Connect the terminal of the wave to a single coil guitar pickup at 2000kHz and through the pickup wires I got a constant and stable 84mV signal, tested with the multimeter and which remained on Pin 2 during the measurement.
Do you recommend otherwise? I hope I don't hinder your help much ...
Thanks again Robert!
J
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84mV is fine, 1kHz should also be fine
I wonder, why you measured 0,000 the first time
Maybe there was a contact issue
Try inserting the signal not directly at the pin of the tube but to the input jack. You want to measure the signal chain of the amp and not just single stages. V2b needs the signal already processd by v2a in order to interpret the measurement right
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Not sure with the guitar pickup thing though. Connect the 2v signal to a potentiometer, connect the ground lug of the pot to the gnd of the signal generator and dial in something between 50 and 100mV
The square wave is also not ideal. Multimeters return an ac measurement as an RMS (root mean square, an „average“) value, which is 0.707 times the peak to peak value of an (assumed) sine wave. A Square wave behaves different on a multimeter, it is either fully positive or fully negative, no rising or falling, so an RMS is supposed be the full peak to peak voltage during the entire cycle.
Sqare wavwes are rather used to visualize the transient response on a scope
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Btw: i built my frequency generator using the XR2206 chip
It is kind of cheap, you need just some external parts and a battery. Not super precise but very handy for audio testing
Google for projects or just use the datasheet
I took mine from www.dieelektronikerseite.de
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Hi Robert,
I have followed your advice and built my frequency generator using the XR2206 chip. The measures:
Signal 0.051 V
V1 (V, AC) : Pin2: 0.051, Pin1: 2.04, Pin7: 0.07, Pin6: 1.57
V2 (V, AC): Pin2: 0.074, Pin1: 0.8, Pin7: 0.011, Pin 6: 0.7
Blast (V,AC) middle lug 0.041
Thanks,
Jaime
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Hi Jaime,
Wow, you are quick – congrats to your new frequency generator. :topjob:
Here an overview of your measurements in the order of the signal path:
Stage Input Output Ampl.-Factor comment
V1a 0,051 2,04 40,0 ok
Blast ??? 0,041 ??? Input value is missing
V1b 0,07 1,51 21,6 seems too low, try a different preamp tube and measure V1a and b again
V2a 0,074 0,8 10,8 both inputs and outputs are supposed to be roughly equal
V2b 0,011 0,7 63,6 but aren't
If your measurements are correct, there is something wrong in your PI.
The principle of this kind of Pi is, that the first tube amplifies the signal and inverts the signal and feeds the first power tube.
The second PI-tube-half must deliver a signal of the same amplitude in the opposite phase. Therefore the signal of the first tube is tapped, a voltage divider attenuates the tapped output of the first half and feeds it into the input of the second tube half.
The second half amplifies and inverts this signal and the output goes to the second power tube.
In your case the output of both halves is drastically different. I assume, Dirk’s published circuit is correct and tested, so there must be errors in your build.
Please check all the component values around your PI.
The amplification factor of V1b seems very low too. Please check the component values too.
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jejeje I have done it quickly because I have a tremendous desire to enjoy this amp!
I have changed tube 1 for a 12AX7AC5 HG that I had at home.
New measures....
Stage Input Output
V1a 0,057 2,1
Blast 0.346 0,043
V1b 0,042 1,4
V2a 0,048 2.0
V2b 0,028 1.9
I check "nuevamente" the preamp section...
Thanks Robert!
J
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Hi Jaime,
looks a bit better now:
Stage Input Output Ampl.-Factor comment
V1a 0,057 2,1 36,84 ok
Blast 0,346 0,043 0,12 ok
V1b 0,042 1,4 33,33 ok, it seems, your first tube had an issue
V2A 0,048 2 41,67 much closer than before but still odd
V2b 0,028 1,9 67,86
in general I think, 2V output from the phase inverter can't be enough to drive the 6V6es to full power. But we have the blast set to 12 o clock which equals roughly to 10% (confirmed by your measurement above). What voltages do you measure when you crank the blast control full up?
There is something strange: the Output of V1B is 1,4V, after it there is the tone stack, a passive circuit which in theory (and in reality) attenuates the signal by up to -20dB (equals to factor 0,1). But the signal entering the phase inverter is 2V instead of the calculated 0,14V. This is confusing, instead of attenuating the signal the tone stack amplified the signal which is impossible. ???
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when I crank the blast control full up the measure the same in output and input: 0.324 V.
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Hallo zusammen, sorry wenn ich Thread gerade etwas hihack aber ich hätte auch eine generelle Frage zu hohen Spannungen und möchte keinen eigenen Thread deswegen aufmachen.
Ich habe beim Emma Bausatz den TT-30T-V2 Trafo mit erhalten. Die Emma singt wunderbar, mich machen nur die etwas zu hohen Spannungen nachdenklich, die hauptsächlich höheren Ausgangsspannungen des Trafos geschuldet sein mögen.
Bei 231 V Netzspannung messe ich am Eingang der mini PSU 220V. Heizungsspannung 6,6V
B1 272 V B2 260V B3 256V , belastet, also mit Röhren drin.
Gemessen mit kalibriertem Fluke Multimeter (Batterien neu :P)
Ist das noch vertretbar und sollte ich irgendwo Nachsteuern?
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Hi,
New double check of preamp and power section without finding any errors ??? ??? ??? :P :-\ ... both components and lines. I am beginning to think about this is de real BFlex sound and it is what it is... :-\ :-\ :-\ :-\
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Hi Jaime,
Just deleted my post. Noticed you measured already all pins of each tube.
Cheers
Laurent
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Hi Jaime,
the blast pot works fine, ok. But what signal levels dou you measure in all stages when it is fully open?
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Thank you for yours answers!
Robert, do you mean to repeat all the previous measures with the blast pot fully open at the preamp section or at the power section too?
J
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Stage Input Output Ampl.-Factor comment
V1a 0,059 2,83
Blast 0,33 0,33
V1b 0,32 6,7
V2a 1,66 21,7
V2b 0,70 19,5
V3 Pin5: 21,6 Pin3:61,2
v4 Pin5:19,5 Pin3 62,5
Speakers:
J5 5,6 V (AC)
J4 3,9 V (AC)
J3 2,7 V (AC)
All measures are AC, Does is OK?
I have a question with the Bias Trimmer. The middle lug is welded on R 103 along with the side lug, is that correct?
I attach a picture.
Thanks,
Jaime
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I have a question with the Bias Trimmer. The middle lug is welded on R 103 along with the side lug, is that correct?
Yep, thats right...
blues
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Hi Jaime,
At pins 3, did you forget a "3" for the values? Or did you really measured 60V?
Laurent
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Thanks Blues for your answer...
Yes Laurent, I measured again:
Signal: 0.06 V
V3:
P5: 21,6 V
P3: 65,9 V
P4: 3,0 V
V4
P5: 19,5V
P3: 66,6V
P4 5,3 V
All AC measurements and GND to chasis, is it OK?
Thanks,
Jaime
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:facepalm:
Should have read the posts before...
You measured the AC signal. now I got it.
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I don't quite understand what you mean...
Have I already done something wrong? ... could you tell me how to make the measurements or where to find it?
Thank you very much, Laurent
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I'm just building quickly the schematic on LT Spice following the schematic you posted above and I wonder whether you wired C8 correctly. The way your green lines are drawn, I could think, it's wrong. Can you check it?
C8 has no connection to R13 and R14. It goes straight to P3.
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Thanks,
I check it and C8 does not have continuity with the resistances. In fact, he had protected one of the C8 terminals (blue sheath) to ensure that it did not any contact...
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Hi Jaime,
This is what you should get at the input of the 6V6 with:
1- BELLS/BALLS at 12 o'clock and BLAST also (HALF). You should read about 11Vrms at pins 5 of the 6V6.
2- BLAST fully opened (FULL). Here you should read slightly over 30Vrms, even if the DMM will get wrong because you do not have a sine anymore.
Pics shows with a bias voltage of -34V. No idea what you have.
As you seem to get a low swing out of the PI, I assume that the PI wiring contains a mistake. You should try to get fresh air and then slowly and accurately check again all connections. Maybe you could start with new prints of the schematic/layout to make sure, you start with a new mind.
What value does the feedback resistor have (measured) ?
Laurent
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ufffff :facepalm: :facepalm: :facepalm:
Thank you very much Laurent for your dedication, time and help. I have reviewed all the amp 5 times (yes... 5 :facepalm:), including 2 more during the assembly of each section and checking the value of each component with a transistor tester before placing each one ... I sure if I review again, in the same way, the result will be the same ... Probably the problem is my lack of knowledge...
Where could I get a fresh and easy vision on how to check the amp (I looked it up in the forum and I couldn't find it)
and Could you tell me about how I measure the value of the feedback resistor ???
Thanks,
Jaime
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I calculated the bias as Robert told me a few days ago and adjusted it with the trimmer around 22-24mA.
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The bias should be ok. I saw you have -33V at the beginning of the thread.
The feedback resistor is R23 on the schematic.
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And don't be too rude with you. We all start from somewhere. Give you 1 day break with the amp.
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I just see that you also measured the anodes of the 6V6.
There is something wrong. With 20V at the input, you get no swing for the output (only 60V).
How did you wire the output transformer? I think that the TT transformer has several taps on the primary. Which colours are wired where?
But Robert might have better recommendations regarding your measurements.
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The R23 measurement: 14,64 KOhm
The TTOutput:
Blue and Brown wires solder to Pin 3.
White wire to B1.
Pink, orange, grey wires solders to 4,8,16 Ohms jacks speakers...
Black to GND chasis.
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Everything seems ok.
There must be something but what ???
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Now that I haven't worked in the amp for a day, where do you recommend that I start again to check the amp?
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Hi Jaime,
Sorry, I didn't see your post yesterday...
I rechecked your measurements.
If those are right (the last ones at bottom of page 3), the first thing to look at, is the output stage. The swing out of the tubes compared to the input, does not match. The amplification factor (mu) of the 6V6 should lay by about 15-20 with that wiring. Here you have only 3.
One item could lay at the feedback, but you checked the resistor value. Recheck all the wiring of this area as well as the voltages.
Just for understanding: which dummy resistor do you use and where/how do you connect it?
Laurent
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I use a 4,4 Ohm 10 W dummy resistor solder to a 6,3 plug and I swith on to speaker 4 Ohms entry, is it OK?
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Hi,
10W is definitely too low. 2 6V6 in Push-pull, will deliver 15-20W. As the resistor has probably no heat sink, I would take a 50 W as minimum.
Laurent
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NEW MEASUREMENTS!!
WITHOUT SIGNAL
At home 220.1 V (AC)
V1 Pin 1: 186 V
Pin 3: 1.71 V
Pin6: 175 V
Pin 8: 1.42 V
V2 Pin 1: 235V
Pin 3: 1.68 V
Pin 6: 220 V
Pin 8: 1.55 V
V3 Pin 3: 378 V
Pin 4: 376 V
V4 Pin 3: 377 V
Pin 4: 376 V
B1: 378 V
B2: 376 V
B3: 328 V
B4: 319 V
BIAS: V3: 17.4 mA
V4: 26.1 mA
The 6V6 tubes, in theory, are matched, but is the difference acceptable?
WITH SIGNAL
Signal: 0.058 Dummy resistor: 8.9 Ohm 50 W
BLAST and all HALF FULL
Stage Input Output Input Output
V1a 0,058 2,34 0.058 2.34
Blast 0,049 0,33 0.41 0.41
V1b 0,05 1,5 0.25 6.7
V2a 0.058 2,0 1.64 20.1
V2b 0,029 2.0 0.65 18.0
V3 Pin3: 20 75.5
Pin4: 0.5 3.7
Pin5: 2.0 20.0
v4 Pin3: 20.5 75.7
Pin4: 0.5 5.5
Pin5: 1.9 18
Speakers:
J5 (AC) 1.8 6.8
J4 (AC) 1.2 4.7
J3 (AC) 0.9 3.3
what do you think?
Thanks,
J
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Hi,
At first sight almost everything seems to be ok. The DC values are on track. The AC values also, apart from the output swing out of both the 6V6. I can't understand why you get such a low swing. The input at the 6V6 is for my taste a --- low but that can lay at a lower gain of the PI tube. Anyway, your problem is at the output stage. The PI seems to do his job in term of bringing a signal to the 6V6.
The difference of idle current is surely quite high but should not be an issue. Anyway, matched tubes live their own life after they are running under real conditions. Matching is mostly done at 1 single point of measurement. This does not indicate whether the other matched tubes have a very near characteristic. Anyway, this should not be the problem of your low output power.
If we assume that your tubes are both new and matched, the probability that both are nearly dead is very low - these are not sensitive transistors.
That means that this low output swing out of the tubes is limited through (maybe) an odd reflected impedance from the secondary winding of the OT to the primary of the OT, which is connected to the 6V6. As you seem to have wired the OT properly & your output jacks are wired the proper way, the OT must get checked.
You have the choice to unwire it completely or to leave it in place as is. Just remove the 6V6 in this latter case, in order to make sure that none of the wires is connected to anything.
But you should unwire the CT, in order to make sure, that you have no connection to the supply rail. Secure it and make sure you can access it for measurement.
Then:
1- Take the datasheet of the OT from the shop product page
2- Measure all DC resistances and compare them with the datasheet. Are they all in the ballpark where they should be?
3- If everything OK, we can move to the AC test. Connect the signal generator to the secondary at the 16 Ohm jack.
4- Then feed a simple 1V signal.
4- Check at the primary what you get between plate-CT-plate ? The plate-plate measurement gives you in this case the turn ratio of the transformer. For this OT at the 16 Ohm, you should get around 22V at the primary.
5- If ok, move the signal generator to the 8 & 4 Ohm taps. You should get around 32V and 45V between the plates. Also check what you get between the plates and the CT.
If everything still ok, then we could feed 5V and repeat to see, what you measure. But first make the measurements and post them, so we can see, what you get.
But if everything is fine, I have no clue, what happens...
Laurent
EDIT: having had another trouble in the past with a cold solder joint at the CT, maybe try to check this one first, even if your DC measurements seem to be ok.
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Thanks, Laurent!
I desolder the secondary winding, desconnect the CT white wire and pull-out the 6V6 tubes and the measurements:
secondary OT
pink-black 0.2 Ohm
pink-brown 0.1 Ohm
brown-grey 0.2 Ohm
Primary OT
white- blue 86.3 Ohm
white-brown 88.5
Are there any problem in the secondary OT?
I attach the OT datasheet.
J
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I think it should be ok at the primary. Secondary is difficult to measure without proper equipment.
Let check the AC behaviour now.
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done!
[Signal 1V (AC) secondary OT 16 Ohm
Primary OT
White-blue (CT-plate) 4.63 V (AC)
White-brown (CT-plate) 4.64 V (AC)
Blue-brown (plate-plate) 8.85 V (AC)
Signal 1V (AC) secondary OT 8 Ohm
Primary OT
White-blue (CT-plate) 3.71 V (AC)
White-brown (CT-plate) 3.74 V (AC)
Blue-brown (plate-plate) 7.01 V (AC)
Signal 1V (AC) secondary OT 4 Ohm
Primary OT
White-blue (CT-plate) 2.88 V (AC)
White-brown (CT-plate) 2.85 V (AC)
Blue-brown (plate-plate) 5.47 V (AC)
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If I'm not wrong, there is something really odd there...
You should get on the primary the approximative values I wrote above. This is not the case for the specs I roughly evaluated.
Maybe somebody can confirm that? Robert, you gave already a lot of advices, what do you think?
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To confirm that the measurements have been made correctly and I have not made any mistakes ...
I have connected the signal to the desoldering secondary wiring directly and measured the primary voltages by removing the valves and disconnecting the white CT wire, is it right?
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:urlaub:Yes, perfect.
To exclude all potential issues linked to the sockets, you can desolder the 2 wires left (plates) and repeat the AC measurements. If they meet the same values as before for the first set of measurement, then this is like it is. The OT seems to have an issue. I explain you afterwards why I say that.
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Laurents, the same after desolder the primary wires blue and brown...
[Signal 1V (AC) secondary OT 16 Ohm
Primary OT
White-blue (CT-plate) 4.6 V (AC)
White-brown (CT-plate) 4.5 V (AC)
Blue-brown (plate-plate) 8.7 V (AC)
[Signal 1V (AC) secondary OT 8 Ohm
Blue-brown (plate-plate) 7.0 V (AC)
[Signal 1V (AC) secondary OT Ohm
Blue-brown (plate-plate) 5.5 V (AC)
Thanks,
J
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So, in the attachment you will see why it cannot work.
Your OT seems to have a defect.
According to this state, the reflected load is about 300-500 Ohms !! No power out, but not good for the tubes either.
The theory behind the table in attachment:
The voltage relationship U1/U2 (1=primary, 2=secondary) is equal to the turns ratio N1/N2 (let speak about an ideal OT).
In the datasheet, this ratio is not given. We can calculate it from Z1/Z2, as Z1/Z2=(N1/N2)^2 as an approximation - fair enough.
This is what I did in the excel file. I did this small table long time ago to check also an OT. ON the right hand side, I integrated your measurements and you see the result of reflected load compared to the specs.
The OT seems to have a problem.
Before having tested anything with your small 10W resistor for this thread, did you run the amp without load? Because you had this trouble before the first measurements at full blast.
If you have the components, you can also check the OT for an internal short, I attach you the doc. But the OT needs to be changed apparently :(
At least the root cause is found. Do not give up!! Keep strong and positive, that could be worse !!
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And here this is what I get in the spice simulation, adjusting the OT so that I match the measurements you just made...
This is exactly what you measured 2 days ago: 6,8Vrms at the 16 Ohms output jack. I matched the signal level at the input of the 6V6.
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Yes, I run the amp with the speaker... and the volumen was very low... The volumen problem started at this point, since I turn on the amp when I finish it...
I'm tired but I am very happy to find the problem. I already know the memory circuit from the times I have reviewed it ... Will the problem be solved by changing the OT?
A lot Thanks for your time and help!
J
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Yes, it should solve the problem. But I wonder why the OT is down. The shop delivers quality OT, so there must be a reason why the OT is now as it is.
I'm just worried, that a new one gets shot again.
And no idea if the 6v6 are still ok, as I have no clue how they liked the test sessions at full blast with the steep reflected impedance.
Your 10W resistor was actually ok, as the delivered power was very low from the start. I was just worried that you used it at full blast before testing the amp with an instrument. Then you might have damaged the OT.
Also, as you checked your build several times, measured everything several times and that was ok, it seems that the OT may have been like this from the beginning. Surprising but possible, if they are not tested for function by the manufacturer (what I doubt for that one).
I would suggest you to get in touch with the shop using the standard manner (form in the website or email), explaining your issue, and the steps you went through.
Laurent
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Thank you very much Laurent and Robert for your help!
I contact the store ...
Best Regards,
Jaime
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Yes, it should solve the problem. But I wonder why the OT is down. The shop delivers quality OT, so there must be a reason why the OT is now as it is.
I'm just worried, that a new one gets shot again.
das ist genau der Punkt. Die Erfahrung zeigt, dass ein defekter Transformator in der regel nicht die Ursache sonder das sichtbare Ergebnis für einen Fehler im Aufbau ist, insbesondere wenn man bedenkt, dass die Übertrage mit 1kV oder 2kV getestet sind.
Normalerweise gehört so ein Verstärker ordentlich geprüft.
Gruß, Dirk
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I am interested in enjoying the amp now and for many years. After all the checks we've done on the amp: visual, static and signal tests, we couldn't find any problems (except OT). How do you recommend that we verify the amplifier correctly, Dirk, to definitively rule out a structural mistake in the device?
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How do you recommend that we verify the amplifier correctly, Dirk, to definitively rule out a structural mistake in the device?
The answer is simple: in a tecnical correct way. This includes voltages, current, oscillations (with a scope), power and heat.
Best regards, Dirk
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Hahaha... ;D
And I was nervously waiting for your answer to illuminate the doubts to enjoy the amp with my jazz bass... :guitar:
jajaja! :facepalm:
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Hi,
Do not give up with the nerves.
With the remote servicing as we do here, we are at the limit of what we can do. My doubts remain concerning the very root cause of the problem with the OT. Maybe you can find a serious and capable tech in your area so that he can have a look at it ?
Anyway a new OT needs to be installed but beforehand a complete check would be safer.
We also have no clue, how you checked the amp before the first time you ran the amp with tubes. There are many steps involved to ensure safety and proper wiring in order to avoid a bad experience.
So I would strongly recommend you to find a local support as soon as the quarantine is over in Spain (or is it already?)
Laurent
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Thanks Laurent, you are an angel!
I will follow your advice and tell you the final results!
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Hallo,
the Amp finally arrived at our workshop, we tested it and can not find any problem. Well, one of the powertubes was slightly worn ( maybe because of the troubleshooting ? ) so the total power with this tube was 18 Watt, with a new powertube the power is now 20 Watt which is perfect. Everything else is also fine, we can not find a problem.
I guess that you expect a much higher volume and did not check any of the parameter or the power but started to search for none-existing bugs.
Best regards, Dirk
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Thanks Dirk!
Dirk, It's a good and bad news ... Good news because the amp work fine, like you say. Bad news because I continue to have a problem. I'm looking for a amp to play bass at home. I built few years ago a 5E3 amp (18w, and I can't turn up the amp volume and the guitar volumen of more than 50% without being afraid of glass breaking) and Madamp G3 (3w that I can play at home without having fear that the neighbors will call me). When I connected the BFlex (amp volume Full and bass volume Full) and the Madamp G3 (amp volume Full and bass volume Full ) to a Jensen C12N (8 ohms) and a Hartke 15 '(8 ohms), the Madamp G3 sound little louder than Bflex ... Could I expect more power from BFlex amp?
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The power of the BFlex is around 20 Watts, and this is what we measured with your amp. I do not know what loudness you expect but the BFlex should be loud enough for home use and also small stages. If the amp is not loud enough for your needs than you must use an other amp. I do not know your setup and what else you use so I find your error description difficult to categorize. I just can tell for sure that the amp works as it should.
Best regards, Dirk
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Dirk, everybody know the quality and the interesting of your amp designs and the quality and seriousness of your work. I hope I can enjoy your personal version of the 5E3 soon...
I am sure the design of the BFlex is great for playing bass and that it has to meet my needs. In that sense, I don't understand why it sounded so low at home. Hopefully the trip to Germany, the tube change and the resoldering of OT it's sound fine too. Thanks for the help, Dirk.
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Hallo,
we compared the BFlex with the 5E3 and the loudnes is almost the same but the 5E3 is overdriving a lot so if you want a clean bass sound you must lower the volume so finaly the 5E3 is not as loud as the BFlex.
Best regards, Dirk
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Hi,
I'm not sure whether this has been suggested earlier but you might want to try a different speaker with a higher sensitivity.
Best, Peter
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...and / or an array of more efficient speakers (e.g. a 4x10 cabinet). Thus you will benefit from the higher sensitivity AND the increase in level by using more speakers (doubling the number of (the same) speakers will increase the sound level by 3dB)