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In Reply to: RE: 450v plate and screen? posted by Alpha Al on June 08, 2017 at 13:56:49
Check the screen current and see what you find. That might be quite helpful.
I changed to a pair of JJ 6V6S, they don't have the hot spots.
Normally, I stay away from JJ octals, but in this case, they fixed it.
I think the TungSol was a defective pair.
The screens are drawing 2 mA each with either tube type.
That definitely could be the case. I've had ONE case of the 6V6GTs acting up in all the years I've had them. And many have been used at 425 -450 volts. But it can happen... Hopefully the vendor will stand behind yours!
Al, on many Fender amps... changing the screen resistors to wire wound or metal oxide, 5-watt 1k-ohm usually helps stabilize the output tubes.
My DR runs over 450VDC on the plates. I bias them to about 20mA per tube.
Photo is of my Super Reverb, I put 1k-ohm bricks onto the screen grids.
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