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

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

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

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

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

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.

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

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. 

when I crank the blast control full up the measure the same in output and input:  0.324 V.

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  )
Ist das noch vertretbar und sollte ich irgendwo Nachsteuern?

Hi,
New double check of preamp and power section without finding any errors  ... both components and lines. I am beginning to think about  this is de real BFlex sound and it is what it is...

Hi Jaime,

Just deleted my post. Noticed you measured already all pins of each tube.

Cheers
Laurent

Hi Jaime,

the blast pot works fine, ok. But what signal levels dou you measure in all stages when it is fully open?

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

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