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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 01 May 2017, 06:11 
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This has probably already been looked at,

Here are a few thoughts:
I have seen comments that the cathode voltage is stable, however the bottom line is:
Is the cathode current correct? Monitor it at start up until red plating occurs.

Is there any coupling between the power transformer and the output transformers?
Is there a bypass cap on the cathode carrying ac current?
With the connection to the coupling cap removed ie no input to the output tubes do they still red plate?
Is there chassis magnetic linking to the OP Tx's lift the transformers off the chassis.

If the cathode current is correct exactly at the output from the tube and it red plates then is the heater voltage correct?
If all else fails what's the temperature of the tubes red plating compared to the ones running correctly?

Just a few ideas.
Regards
M. Gregg

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PostPosted: 01 May 2017, 06:23 
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One more thought,

Is there any heater cathode leakage?
Ie is there a power Tx short?

Try using a different method of heater lift or ground.

Just a couple of ideas to try..
Float the heaters with a polypropylene cap.
Here is another to try BE CAREFUL, isolate the power Tx from the chassis and check leakage between iron circuit and ground.

I have had some real messed up heater windings on Hammond power Tx's...

Regards
M. Gregg

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PostPosted: 01 May 2017, 07:23 
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Here is another thing to try,

Monitor the anode current and cathode current at the same time.

Cathode should be the anode + a few mA for grid current (obvious).
If there is a difference where is the difference?
Compare to a none red plating tube.

Monitor heater grounding current and compare.

Regards
M. Gregg

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