Old Fender fiber boards

[frankeg]

Yep, about 13 watts, I agree. And they are EH tubes. I'm trying to talk my friend into going back to a tube rectifier and/or perhaps get one of webers copper cans (diode rect in a can that fits the tube socket) so he can go back to SS if he wants to (but I don't think he would).

Joe, I'm slightly confused here but I measure from the plate of the pwr tube to the center tap B+ connection of the ot. The fluke can do this accurately due to it's extremely high impedance. I read the current for each tube this way. So, the 31 ma is for one tube and as pointed out above by mwjb that means I have 420 vdc X 31 ma = 13 watts...

[MWJB]

You shouldn't ever fit a SS rectifier to a tolex Princeton, or Deluxe/Deluxe reverb. 30mA is too hot for an EH, Fender uses them in the RI BFPR and biases to around 10-11W...go back to the tube rectifier, or a copper cap & bias to 23mA/tube, the EH can take the over voltage, but not oodles of current.

If you want the option of using the SS rectifier install a reverse polarity zener diode in series with the B+ centre tap to bring the B+ down 30-40v.

[frankeg]

You can bias them to 50-60mA if your plate voltage is low enough - DON'T try it in a Princeton though, the voltage is way too high!

I make this mistake often when emailing... I assume that whats in my head you already know. It's fresh to me cause it's my issue... What I left out though you know from experience which is the plate voltage at around 420 vdc in the Princeton. So, as you figured, I was saying 31ma at 420 volts.

[frankeg]

You shouldn't ever fit a SS rectifier to a tolex Princeton, or Deluxe/Deluxe reverb.

I didn't do this. It was done by a mod in the 80's. The same mod that added that cathode pot I mentioned in my 1st post. I did recommend going back to a tube rectifier to the owner. I'll talk to him again and at least have it re-biased.