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6AN8 Pre & concertina, what seems to be the problem?
6AN8 Pre & concertina, what seems to be the problem?
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Old 22nd November 2017, 07:24 AM   #1
Junm is offline Junm  Philippines
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Default 6AN8 Pre & concertina, what seems to be the problem?

I had a problem with the power amp section of a Sansui-1000A. trying to restore this thing. upon voltage check the supplies voltages are okay except of the things in red mark values. This is common to both channels. Clean tube pins and connectors and interchange the 2 tube and still got the same reading. Change coupling caps and still can't get the same DCV Value (In Black).

What seems to be the problem, need your help please?
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Old 22nd November 2017, 07:51 AM   #2
TonyTecson is offline TonyTecson  Philippines
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6AN8 Pre & concertina, what seems to be the problem?
try a new pair of 6an8's
check resistors that have drifted away from original values
especially carbon comps...

even with new tubes, i doubt that you will get the same exact readings, close enough is good to go..
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Old 22nd November 2017, 08:04 AM   #3
Junm is offline Junm  Philippines
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I tried measuring resistances and still same readings .voltage readings are very far from the said value. I also guessing that it was the tubes but it happens to both channels. I just want to try 6GH8A but they don't have the same pinouts.

I tries to lowered the value of plate resistance of the pentode and reads higher but VG2 still peg at 20v. Lowered VG2 resistor to half but it pulls down the plate voltage again to 25v so remove the resistor and back to 60vdc plate. tried to play music, it sounds but too weak.
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Old 22nd November 2017, 08:08 AM   #4
TonyTecson is offline TonyTecson  Philippines
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6AN8 Pre & concertina, what seems to be the problem?
try replacing all e caps at the pentode side and psu line...
check that 150pf caps have not turned leaky,
i
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Old 22nd November 2017, 08:41 AM   #5
Junm is offline Junm  Philippines
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Yes Sir I will try to recap this thing on the next sitting. if it will still be the same I will replace the 6AN8 pair.
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Old 22nd November 2017, 08:45 AM   #6
TonyTecson is offline TonyTecson  Philippines
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6AN8 Pre & concertina, what seems to be the problem?
if you have the russian 6f12, you can try it too..
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Old 22nd November 2017, 08:48 AM   #7
Junm is offline Junm  Philippines
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Yes I have several of this, but different pin out...rewiring will be needed.
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Old 22nd November 2017, 12:25 PM   #8
artosalo is offline artosalo  Finland
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At first, what is your voltage meter ? What is it's input resistance ?
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Old 22nd November 2017, 12:59 PM   #9
Ketje is offline Ketje  Belgium
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Here is something wrong
Mona
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Old 22nd November 2017, 02:39 PM   #10
Junm is offline Junm  Philippines
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Quote:
Originally Posted by artosalo View Post
At first, what is your voltage meter ? What is it's input resistance ?
Supply voltage is indicated in red marks. I tried to put 500k on grid 1 to ground but no effect.
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