1

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 29, 2026, 05:29:16 AM »

I found it at last! there was a tiny solder bridge between pins 3 and 4 on U2. Thank you so much for your help and patience?
Cheers!
-Ben

2

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 28, 2026, 12:33:29 AM »

I have 1.65vac at pin 5 of U1, voltage doesn't seem to get to pin 7, I have tested R15, R16, C9, C10, C11 multiple times and all appear good and the traces all seen ot have the correct continuity with the components.  I've also swapped the op amps and get the same result.

3

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 27, 2026, 08:27:50 PM »

I get:
1  0vdc
2  0vdc
3  0vdc
4  -15vdc
5  0v
6  0v
7  0.05vdc
8  15.37vdc

4

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 25, 2026, 07:21:16 PM »

I still keep running into no signal at TP4 with and without the front panel and U2. I've verified every resistor and diode on the board. What should I try next? 
Thanks, 
Ben

5

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 18, 2026, 11:01:38 PM »

I'm stumped, Now I lost ac voltage at TP1 and I still get 1.64vac at TP3 and 0.055vac at TP4
I still have 30vdc at TP1 and 2 as well.
Just to confirm, what value should I be getting on P1? the impedance stays at 0 when turning the pot on the right 2 pins when looking at the pot from the rear, It varies between 0 and 10k on the left 2, I get 10k on th outer 2 pins

6

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 17, 2026, 09:21:04 PM »

I get no signal at TP4 with the front pcb removed, power on. With and without U2. Solder joints and component values seem to be good.

7

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 16, 2026, 04:19:05 PM »

I have 1.22vac between TP1 and TP4 and 0.058vac between TP0v and TP4 with U4 removed

8

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 16, 2026, 06:42:36 AM »

Now I get 0vac at the output


i get 200 ohms between r1 and r2 on the legs closest to the face plate, after finding an issue with pin 10 on the T1 pcb.

R1=2.191k

R2=2.188k

I get 657mv across pins 7-10 of T1 and 269mv across pins 2-5 with power off and 1vac input


TP1 = 29.92vdc
TP2 = 30vdc
TP1 = 1.23vac
TP2 = 1.16vac
TP3 = 1.63vac
TP4 = .054vac
Input 4.57k ohms pin 2-3
29.97vdc and 1.22vac TP1 to TP4 with U4 removed


Thank you for your help!
Ben

9

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 13, 2026, 06:58:31 PM »

I get 0mvAC across T1 pins 2-5
I get 67mvAC across T1 pins 7-10
power off 1vAC on input.

T1
pin 2-4   37.1 ohms
pin 2-5   37.3 ohms
pin 7-9   99.9 ohms
pin 8-10  100.6 ohms
input pin 2-3  14.14k ohms (this looks off)

Thank you

10

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 11, 2026, 09:23:01 PM »

Apologies, my DMM lead must have had a bad connection testing TP2. I actually have 29.79vdc and 0.145vac @ TP2. TP3 is the same

11

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 07, 2026, 04:22:11 PM »

Sure can, 
TP2= 0.297 VAC and 0.057 VDC
TP3= 0.077 VAC and 0 VDC

Pot 1, R1 and R2 test ok as well
Thanks,
Ben

12

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 03, 2026, 05:05:53 PM »

I reheated all solder joints and rechecked for bridging or shorts, no change
Thanks,
Ben

13

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 01, 2026, 07:50:42 PM »

 0.05vac and 29.69vdc @ TP1
0.077vac and .258vdc @ TP4

14

MU524 Vari-Mu Tube Compressor / Low output voltage step 6

« on: March 26, 2026, 06:40:57 AM »

I am only getting 0.152v ac on the output when engaged. I believe the transformer is oriented correctly and solder joints appear clean. I am getting 0.14v ac @ U2 pin 4 and U2 has power. I hear the relay click when taking out of bypass. I also tried cleaning the tube pins. Please advise, Thank you
+15.6 v
-15.56v
B+ 45v
tube heater 6.15v and glowing