Fender Blackface Tremolux RED HOT

[themusic]

I have a Blackface Tremolux that red plates first 6L6 immediately. Somebody has taken the rectifier and converted it with a solid state mod.
I think that was done before the amp started having problems, or is now the problem . Pulled tubes and started checking voltages. testing 345vac out of transformer to pins 4 & 6 of the rectifier and +525v at pin 8.
Schematic shows it should be around 415v. Is this a common mod to the rectifier ?
Pin outs at first 6L6 read 3-3.4vac 4-522 vdc 5-522vdc 6-331vdc 7-522vdc 8-3.5vac Thanks

[52 Bill]

You need to check the bias supply first. That has nothing to do with the main high voltage power supply.

You need to have somewhere around -50 volts of bias on the output tubes to keep them from red plating.

[nevetslab]

First, I'd guess you're numbering is off by one, as pin 3 is plate (would be 522VDC, Pin 2 is heater (1/2 of 6.3VAC), pin 4 is Screen Grid, would be just under 522VDC, but pin 5, being the input grid, you're showing 331VDC...you've got bad coupling caps between the phase inverter stage and the input grids, which would carry negative bias voltage in the realm of -45VDC. So, yes....it would glow red-hot immediately, with that potential applied.

I'm surprised you're reading that high a voltage at the output of your solid state rectifier module. You do pick up a good 40VDC that 5AR4/GZ34 would drop... depending on how much current is being conducted. With 790VAC C/T on the HV secondary, and solid state rectifiers, you'd probably be in the realm of 475VDC under idle, or a bit lower. 522V seems too high. I'd replace your coupling caps as well as your power tubes,as you may have cooked them if you left it running for any length of time.

[Tom Phillips]

... 5-522vdc...

Is that a typo? If not you have something seriously wrong such as a short between pin 4 & 5.
There should be around -50Vdc on pin 5 of the 6L6.

Note: For clarity it is best not to use the dashes because they get mixed up with minus signs used to indicate negative voltage. For example, use "Pin 5: -50Vdc" and "Pin 3: +425Vdc" Such things will make it easier for people to help you.

The plate and screen voltages will read high when the tubes are pulled because they are not under load. ( Even higher when the SS rectifier is substituted for the rectifier tube)

Cheers,
Tom

[themusic]

Is that a typo? If not you have something seriously wrong such as a short between pin 4 & 5.
There should be around -50Vdc on pin 5 of the 6L6.

Note: For clarity it is best not to use the dashes because they get mixed up with minus signs used to indicate negative voltage. For example, use "Pin 5: -50Vdc" and "Pin 3: +425Vdc" Such things will make it easier for people to help you.

The plate and screen voltages will read high when the tubes are pulled because they are not under load. ( Even higher when the SS rectifier is substituted for the rectifier tube)

Cheers,
Tom

I'm pulling -50Vdc on pin 5 of #2 6L6 ...But on #1 6L6 pin 5 is 330+Vdc thanks

[The Dude]

Unsolder one end of the coupling cap from the PI to that pin and see if the positive voltage goes away.

[themusic]

Yes that got me back to -52Vdc ...I guess looking at that rectifier set up screwed with me thanks...