ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

spitfire clone still red plating

:

6/10/2004 7:02 AM
scott c	spitfire clone still red plating my spitfire is running at 16 watts disipation so dirty told me to add a 5k/5w just before the 100 ohm screens, im still getting red on one tube, im not sure what to do now.

6/12/2004 10:43 AM
Bruce /Mission Amps	1.) Shut it off. 2.) Get those tubes at a lower idle current. 3.) One might be toast already. OK, did he mean in the power supply B+ rail as another filtered dropping node in order to get the B+ to the screens to lower level, or? Bruce

6/13/2004 8:30 AM
scole	yes bruce, i think thats what dirty intended to do but its still not enough. i should probably change the 100 ohm screen resistors to 1500. unless i just change the cathode resistor to a higher value, but i dont want to leave class a bias range.

6/13/2004 1:09 PM
scole	i took some voltages, 10.03 across the cathode resistor, the power tubes both read the same, pin 2 18v, pin 3 10v, pin 7 360v, pin 9 321v. what else should i measure?

6/14/2004 3:27 PM
scole	before i added the 5k/5w, i had 12 volts across the cathode, 352 volts on the plates. how did my plate voltage increase?

6/18/2004 12:18 AM
Dirty	Change the 5K to a 10K and try to get the screens to 270-290Vdc. Then you should be fine with the 120 Ohm resistor at the cathodes.

6/18/2004 12:23 AM
Dirty	Do you have 18V at pin 2 ?!? Then there is a serious problem! Check the couplingcaps!

Page 1 of 3