Author Topic: Low output voltage step 6

March 26, 2026, 06:40:57 AM
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Ben

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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






March 27, 2026, 04:08:55 PM
Reply #1

JPK

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Remove U4.
What values (DC and AC) do you get on TP1 to TP4 in the initial conditions here.
JPK

April 01, 2026, 07:50:42 PM
Reply #2

Ben

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


April 03, 2026, 05:05:53 PM
Reply #3

Ben

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

April 07, 2026, 09:04:14 AM
Reply #4

JPK

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Can you please also report the values on TP2 and TP3?
JPK

April 07, 2026, 04:22:11 PM
Reply #5

Ben

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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

April 11, 2026, 06:49:12 PM
Reply #6

JPK

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TP2=  0.057 VDC
Here is the issue. You should get around 30VDC.
You must check the solder joints on R7, on the tube socket, on the connector that links the tube PCB to the main PCB.
Check that the 48V gets to both sides of R7 (you can check without the tube inserted).
JPK

April 11, 2026, 09:23:01 PM
Reply #7

Ben

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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

April 13, 2026, 11:33:34 AM
Reply #8

JPK

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With a 1VAC signal at the input, IN pot on 10, power off, how many millivolts AC do you get on the input transformer between pins 2 and 5?
JPK

April 13, 2026, 06:58:31 PM
Reply #9

Ben

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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

April 15, 2026, 04:51:24 PM
Reply #10

JPK

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I get 67mvAC across T1 pins 7-10
It should be 650mV!

Check the value and solder joints of R1 and R2.
What resistor do your measure between the 2 left pins of R1 & R2? It should be 200 ohms, the transformer input DC resistance.
JPK

April 16, 2026, 06:42:36 AM
Reply #11

Ben

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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



April 16, 2026, 10:59:14 AM
Reply #12

JPK

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TP4 = .054vac
TP1 to TP3 all good except TP4?

Do you say that TP4 is back to 1.22VAC when U4 is removed? 
JPK

April 16, 2026, 04:19:05 PM
Reply #13

Ben

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

 

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