Author Topic: Tube works, but no output voltage.

May 17, 2022, 06:18:47 pm
Reply #25

n-tn

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Shure, should i measuere the voltages with U1 installed or removed?

May 18, 2022, 03:29:23 pm
Reply #26

JPK

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JPK

May 19, 2022, 01:39:51 pm
Reply #27

n-tn

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Measured between the respective pin and 0V:

  • -0.35 V
  • -4.59 V
  • 0 V
  • -15.09 V
  • 0 V
  • -2.31 V
  • 15.12 V
  • 0 V

May 19, 2022, 05:37:33 pm
Reply #28

JPK

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U1 looks dead. Try replacing it.
JPK

July 04, 2022, 05:49:02 pm
Reply #29

n-tn

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Thanks for your help! I replaced U1 and everything semms normal now, the -5DCV on TP4 disappeared.
However, I followed the Test Guide again and the gain seems lower than expected, when I connect a 1VAC sine to the input and turn the input to max, the LED stays off. Only with gain switch on mid or hight the LED turns green. Same with the output pot to max, the LED only turns red with gain on mid or high... I'm not shure if this is an issue, mybe i just have to wait longer for the tube to warm up...

July 05, 2022, 10:05:19 am
Reply #30

JPK

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Can you do the measurements shown here under "Try to follow the signal"?
JPK

July 05, 2022, 01:38:02 pm
Reply #31

n-tn

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So i did the measuremets and i cant follow the signal :(

  • with gain on mid, pot IN on 10 and OUT on 0:  0.03 VAC on TP1 and the LED flickers green...
  • with gain on Low and both pots on 10: 0.03 VAC on TP3 and TP4


July 09, 2022, 09:42:07 am
Reply #32

JPK

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Not good!
Do you hear the pad relay click when you switch to and from LOW GAIN?
Do you get a better signal level on R8 top pin?
JPK

July 09, 2022, 12:36:55 pm
Reply #33

n-tn

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can't hear any relay click when switching gain...
independent from both pots, i have 0.3VAC on LOW and 3VAC on MID on R8 (I think with top pin you ment the one next to c1), with a 0.5VAC sine wave input.
What realy confuses the shit out of me though, is that there is some sort of passive amplification. With the lunchbox turned off and a 0.5VAC on the input i still get 3VAC on the top pin of R8.

July 11, 2022, 09:35:50 am
Reply #34

JPK

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i have 0.3VAC on LOW and 3VAC on MID on R8
This is good.
The signal doesn't seem to make its way from R8 to TP1. Check the pot P1 and relay RLY2 solder joints.
Do you hear the DI relay click when you insert the DI jack?
Do you get a good output signal from the DI jack?

With the lunchbox turned off and a 0.5VAC on the input i still get 3VAC on the top pin of R8.
Normal: The amplification is passive, done by the transformer.
JPK

July 12, 2022, 03:30:36 pm
Reply #35

n-tn

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So I reflowed all the solder joints on P1 and RLY2 and finaly it works, i was able to complete "Try to follow the signal" with all values aligning as they should. I can hear the relay click when inserting a jack in the DI. However, no click when switching the gain from MID to LOW.

Nevertheless, i finally solderd the output transformer and dont get an audio signal :(. Do you think i Should just reflow the joitns as well and hope it will work or is the problem somewhere else?

July 13, 2022, 09:27:03 am
Reply #36

JPK

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However, no click when switching the gain from MID to LOW
The relay must be particularly silent because your values show that it is working.

and dont get an audio signal
You didn't leave the phase switch in the center position?
Check the solder joints on the phase switch and output transformer.
There is only the phase switch and the output transformer between TP4 and the output. So if you get the good level on TP4, you're almost there.
JPK