Posted by hurdy_gurdyman [ 4.225.234.12 ] on September 05, 2005 at 10:45:56:
In Reply to: Re: Fisher 500C-how hot is too hot? posted by Damir on September 05, 2005 at 06:43:48:
The series resistor for the bias voltage has been completely by-passed a long time ago. There just isn't enough voltage there to reach 26 volts without changing the 15 ohm resistor to ground. The way it is currently hooked up with the 2 ohm resistor replacing the 15 ohm, I am getting:
Plate= 440 VDC
Screen= 300 VDC
Grid= -24 VDC
Also, some time ago I replaced the 1.2 ohm resistor between first and second stage in the high voltage supply with a 7.2 ohm. This is what lowered the screen voltage.
It gets complicated, but it does seem to play well and sounds wonderful. The things I'll do to save money. EL34's are still cheaper than 7591's. Besides, I love the sound of EL34's.
Dave
[ Tubes Forum ] [ Help ]