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Thordarson PA amp conversion

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  • Thordarson PA amp conversion

    I have a ~1949 Thordarson T-31W08 amplifier that I'd like to convert to a guitar amp. It actually won't take that much conversion. In stock form, it's similar to an early Fender Champ, but with a single 6L6 output tube rather than a 6V6, driven by a 6SJ7 pentode. I will, however, be doing a complete tear-down and rebuild. Experience has taught me that's the best way to end up with something that doesn't have weird pops and sizzles in it. I can also implement better grounding practices.

    A "phono" input connects directly to the 6SJ7, but it also has a high impedance Mic input with a 6J7 pentode. My question for the experts is: is there some good use for the 6J7 (or another octal tube)? I haven't tried it, but I have a feeling that a guitar might easily overdrive the 6J7. Maybe a 6SL7 or a single 6J5 stage?

    And we have the standard three pots on the front, Mic, Phono, and Tone.

    I have built Hi-Fi tube amps, and I'm an expert Hammond/Leslie tech. What I know less about is what makes for good guitar preamp/driver gain stages.

    Also, I've noticed that cathode bypasses in this amp--and in many guitar amps as well--are chosen in such a way as to limit low frequency response. Is this a matter of economy or one of purposeful bandwidth limiting?

    The output transformer on this amp is fairly large for a single 6L6, so I would expect it to have decent low-end response.

    Thanks!
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