Other Amps

oh, joy! Tube red,red,red


Looks like its back to the bench for my little 18watter! One of the el84 tube's plate is a pretty cherry red... Hmm. Maybe a leaky coupling cap...or high frequency oscillation? I guess this tube pair should be retired early once fixed.


Check your connections at the socket. Sometimes a dry joint on the EL84's socket can have this affect.


Have not had a chance to look it over. Will swap tube positions if voltages etc, check out. Should be pretty straightforward to see with dvm or scope. I'd be surprised if the tube had failed. ..it's new....but who knows.


I had a Bad Cat that was red-plating one set of tubes and it appeared to be a cathode bias resistor was burnt. I sent it to Bad Cat to repair and upgrade to lifetime warranty.


No problem found... put it on the bench, DC was fine. Tube acted normally. all resistor values ok. the differences in tubes did show on el84 with 4ma from one tubes screen grid and 6ma from the other. 10.5vdc on the shared cathodes. screen is at the same within a few volts of plate B+ , audio isolated by a choke.


I need to put the 15 foot Git cable on the input and see it if occurs. somehow I think its related to an instability with a long cable and the Git plugged in.

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