1

MU524 Vari-Mu Tube Compressor / Re: No AC volage from TP1 on

« on: April 10, 2025, 10:57:38 PM »

U6 had to be replaced with a new one. No voltage came out at the output. 
After replacement everything works perfectly, all measured values are correct.


Thank you for everything,
C.

2

MU524 Vari-Mu Tube Compressor / Re: No AC volage from TP1 on

« on: April 06, 2025, 08:59:19 PM »

The values, directions and soldering of L1, L2, U6, C30-C33, D9, R38, R39, Q4 are correct.
I have no idea what the problem could be...

3

MU524 Vari-Mu Tube Compressor / Re: No AC volage from TP1 on

« on: April 02, 2025, 04:14:38 PM »

I measured it wrong, the resistance is 3.4 ohms.
I tried it with a telefunken ecc189 tube, there is no difference in the result.
It doesn't glow and VAC values are zeros.

4

MU524 Vari-Mu Tube Compressor / Re: No AC volage from TP1 on

« on: March 31, 2025, 08:13:21 PM »

Resistance is 8.9 kohm...

5

MU524 Vari-Mu Tube Compressor / Re: No AC volage from TP1 on

« on: March 29, 2025, 12:01:29 PM »

Tube doesn't glow. Power up the lunchbox: 5,5 V then more to 6.2 V after 10 seconds.
Value, direction and solder joints of L1, L2, U6, C30 to C33, D9, R38, R39, Q4 are correct.
 

6

MU524 Vari-Mu Tube Compressor / Re: No AC volage from TP1 on

« on: March 28, 2025, 01:50:56 PM »

Dear J-P,

Initial conditions:
IN pot @ max
OUT pot @ min
REC pot @ max
Bypass toggle @IN
All Push buttons @UP
Input signal: Sinus 1kHz, 1VAC
Jumper JMP1: removed

Results:
TP1 = TP2 = 45.2 VDC
TP1 = TP2 = 0 VAC
TP3 = TP4 = 0.003 VAC
Output: 0 VAC 

Changed conditions:
Jumper JMP1: on 1-2
Input signal: Sinus 1kHz, 0.3VAC
OUT pot @ max

Results:
TP3: 0 VAC 
TP5: 0 VAC
TP6: 0.345 VDC
Output:0 VAC

Thanks

7

MU524 Vari-Mu Tube Compressor / Re: No AC volage from TP1 on

« on: March 27, 2025, 07:57:24 PM »

Hi,

I measured and experienced the same things, even though the transformer is in the correct position.
What else could be causing this?

Thanks,
C.