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)

[DC]

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

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

Hi jamie,

263V at the wall?

Do you have a fresh battery in your multimeter?


regards
Jochen

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

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

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

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

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

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

[Warning:]

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

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

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?

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

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