Discuss the stuff that makes your ears bleed.
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jimmy74
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by jimmy74 » Tue Mar 16, 2021 10:27 am
I don’t think the problem is V4, otherwise I wouldn’t get any sound through the return at all right? I know that pin 2 is far too loud to get any measurements, I can hear it humming just by getting close to the pin without even touching it. I’ll try pin 7 again this morning
jeremyb
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by jeremyb » Tue Mar 16, 2021 12:10 pm
Input jack wired in reverse?
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jimmy74
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by jimmy74 » Tue Mar 16, 2021 6:29 pm
Tested pin 7 again... now loud hum just a little bump as soon the tester lead touched it... still getting 38v
jimmy74
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by jimmy74 » Tue Mar 16, 2021 6:30 pm
The input jack was working before... and hasn’t been touched
jimmy74
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by jimmy74 » Wed Mar 17, 2021 1:56 pm
Tried replacing all the preamp tubes and still the same result... very low volume on all channels
RectifiedAmps
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by RectifiedAmps » Wed Mar 17, 2021 6:02 pm
Work backwards from V4, focusing on which grid pins (2 and 7) make noise when you probe them. Test both halves of V3- if they buzz/hum, go to V2 then V1.
jimmy74
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by jimmy74 » Thu Mar 18, 2021 1:34 pm
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jimmy74
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by jimmy74 » Thu Mar 18, 2021 1:37 pm
Am getting hum on pin 2 of V3...and v1 and v2 are as silent as they come
RectifiedAmps
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by RectifiedAmps » Fri Mar 19, 2021 12:20 pm
jimmy74 wrote: ↑ Thu Mar 18, 2021 1:37 pm
Am getting hum on pin 2 of V3...and v1 and v2 are as silent as they come
What about pin 7 of V3? That grid voltage is strange. Check the resistance to ground on pins 7 & 8 too. It might be a DC-coupled cathode follower as well- pin 1 might run straight to pin 7?
jimmy74
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by jimmy74 » Fri Mar 19, 2021 1:32 pm
Yes pin 7 branches off to pin 1
jimmy74
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by jimmy74 » Fri Mar 19, 2021 10:39 pm
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jimmy74
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by jimmy74 » Fri Mar 19, 2021 10:41 pm
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jimmy74
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by jimmy74 » Fri Mar 19, 2021 10:42 pm
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jimmy74
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by jimmy74 » Sat Mar 20, 2021 1:45 pm
Pin 7 to ground = 20Mohms
Pin 8 to ground = 100k