Guess what?

mcblink said:
Alright then.
The bias board and pots are on their way towards AMS
Click to expand...

OK
All power disconnected from the amp.
Remove the output tubes.
1. the bias pots have been replaced, re-install the bias adjust board back into the amplifier.

INSULATION TEST one (of two insulation tests)

2. Set meter for ohms.
3. Connect the black probe to pin 4 of the output tube socket.
4. Connect the red probe to pin 5 of the output tube socket.
5. The ohm reading will climb up, up, up.
6. When the meter reading stops climbing up, note the ohm reading and write it down.

7. Measure all 4 output tube sockets (or 2 sockets in 50 watt) as above. Write down the reading for each output tube socket.

8. Report your ohm readings for the above test, report the reading for each / ALL output sockets.

Do not install the output tubes.
Do not power the amp up.
Do not try to operate the amp.
All tests (see above and below) must pass before any attempt to operate the amp.
Do not power the amp up.
Do not power the amp up.
 
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Insulation test one results:

Measuring between pin 4 and 5 of the output socket with the ohm meter.
All 4 sockets (or 2 sockets in a 50 watt) should have the same ohm reading (approximately).

The normal reading is at least 220K ohms or higher for each output tube socket.
The normal reading : you will see the numbers on the meter display rising up, up up, higher and higher.
Then the meter will read approximately 220K ohms steady.

If the number stays low and does not climb higher and higher: there is a problem with the main circuit board.
The insulation between high voltage and low negative bias voltage has broken down / is failing.

The board must be replaced or repaired --then repeat the test.
If the above test fails:
there is no point in doing anything more until the board passes ---- insulation test one.

The New Board can be installed.
The Dr. Tube Steady Bias Mod can be installed to repair an old board.
Either one of the 2 should be acceptable.
Then - repeat the test---until it passes.

Next Then proceed: To the next test. This will be the negative bias voltage test.

Do not install the output tubes.
Do not power the amp up.
Do not try to operate the amp.
All tests (see above and below) must pass before any attempt to operate the amp.
Do not power the amp up.
Do not power the amp up.
 
Amp Mad Scientist said:
........
Do not install the output tubes.
Do not power the amp up.
Do not try to operate the amp.
All tests (see above and below) must pass before any attempt to operate the amp.
Do not power the amp up.
Do not power the amp up.
Click to expand...

I read this out loud and summoned Lemmy

Ef0qxMm.gif
 
mcblink said:
Now I just KNOW I have one...or more...of those around here lol
Click to expand...

OK
presuming you have passed the insulation test one, above.
Now you can do the bias voltage tests.

The output tubes are still removed.

9. Set meter to DC volts.
Attach the black probe to the metal chassis.
Attach the red probe to pin 5 of the output tube socket.

10. Do not turn standby to "operate" at any time.
Leave the standby switch in the "warm-up" position.
This will power the amp without turning the HT high voltage on.

11. Connect power to the amp.
Turn the power switch on.
Leave the standby set to "warm-up." Do not turn the stand-by to operate position.

12. Measure the DC voltage at pin 5 of the output tube socket. This should be a negative DC voltage.

13. Turn the bias pot up and down. Verify that the DC voltage on pin 5 of the output socket is adjusting up and down smoothly.
Test both bias adjust pots as above, and measure the DC voltage on all (2 or 4) output tube sockets pin 5.

14. Set the bias pots so that all the (2 or 4) output tube sockets read -42 volts DC on pin 5.
Now double check that all sockets pin 5 read the same DC voltage.

If you are able to adjust the bias pots as above....
and set the bias to -42 volts DC on all output tube sockets pin 5, verified...
Then you have passed the bias voltage test.
 
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So @Amp Mad Scientist has mailed the bias board back towards my way and I await it's arrival.

Thanks for the test procedure AMS, I will get to it as soon as the bias board arrives and I can begin reassembling the nest!

chilipeppermaniac said:
To quote a Cheech's cousin Red in the Next Movie. HOLY SHEEP poop!!!!!!!!!!!!!!
Click to expand...
It appears quite intimidating but it's really not too terribly bad. As I mentioned before, I have torn this thing apart enough times now to where I have stopped pooping my britches every time I open it up
 
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