MajorNut1967
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If you are contemplating using the Electro Harmonix 6CA7 in your older/vintage Marshall, Traynor or with an amp with a negative grid supply; I would stay away from this! The Electro Harmonix 6CA7 is not and I repeat “NOT” a Power Pentode like the original 6CA7’s were, in fact they are Beam Tetrode as stated on the Electro Harmonix website. But the issue is tube venders are saying it is a direct substitute for an EL34 in all situations. Be careful, its not! I you really want to use these tubes in your amps make sure you don’t have a negative grid supply mod or a Traynor Amp. In fact even if your older/vintage Marshall amp has (pin1) & (pin 8) tied to ground, I would stay away from these tubes.
I found this out on my own. My JCM 800 build project was the test bed, I had told Marty I got a set of Electro Harmonix 6CA7’s to try in it later after the amp broke-in, well I put them in today. I couldn’t get them to bias correctly. So I bumped up he bias voltage up and got them in range, but they amp sounded like crap an the PT was hot as hell. Then friggin Wilder clued me in, after all the bullshit I went through, that it’s not a real power-pentode but a damn Beam Tetrode wannabee. Wilder found it out on Solar’s amps, but didn’t bother to tell me! LOL
I found this out on my own. My JCM 800 build project was the test bed, I had told Marty I got a set of Electro Harmonix 6CA7’s to try in it later after the amp broke-in, well I put them in today. I couldn’t get them to bias correctly. So I bumped up he bias voltage up and got them in range, but they amp sounded like crap an the PT was hot as hell. Then friggin Wilder clued me in, after all the bullshit I went through, that it’s not a real power-pentode but a damn Beam Tetrode wannabee. Wilder found it out on Solar’s amps, but didn’t bother to tell me! LOL