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Recycling an old steel chassis from an aircraft surveillance thing.
Replaced central PC board with a piece of 1/8" aluminum, now the small park surrounding the 47. One of two 6.3v filament windings on the PT is 2.5A, so it then sees FWB-LC for 2.5DCV/1.75A for the 47. The dcr of the choke with the draw, accidentally comes to about 2.5 w/o a resistor. It's trying to be a quiet as possible, yet still highish gain, not too loud living room guitar amp that's also LESS powerful than a SE6V6 type amp. If half the power is 3db down, I'll take it. Plus with a higher grid bias to put out half the power, it should be able to take more preamp gain before itself distorts/saturates? This might be good or bad depending on tastes. I don't know what it will sound like yet. Will start with late fifties Fender input and cathode follower driven tone stack, the 5D8 Twin 12AY7 version but include a middle control. The the two stages driving the tone stack are direct coupled so one tube is best for that. That leaves the other twin triode to be the first and last stages.
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If everythings works out- a Marshall 4x12 half stack with a Les Paul plugged in would be be fun!
One of my favorite SE guitar tubes - I used AC filaments into an 8k OPT and had no major hum.Please keep us posted.
Edits: 04/16/14
Interesting DIY project. If you are going to play this amp at "10" ---and who doesn't with one of these flea-powered SE amps. Maybe think about the pentode 6SJ7 (5693) pentode of the earlier woodie era. Mu is in the 12AU7 range. But, the tone is much different than any 9-pin mini driven Fender amp I've used. Much slower onset. Browner. "Women Tone" for lack of a better adjective. The metal cased 5693 is a great tube, IMHO.
You may have seen the photos I've posted of my '48 Champion 600. It has the 5693 front end. No tone control. 6V6GT SE amp. It is a real tone machine. Sounds equally good with Telecaster or Les Paul. Great for recording and bedroom noodling.
Good luck with your project. Tell us how it turns out.
8^)
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Edits: 04/15/14
hi
some good ideas. these low watt SE pentode amps sound great as guitar amps. the overloaded output stage gives tons of second harmonic distortion leading to the unique sound. i've never tried a 47 tho, super cool!
a 6sj7 has much more gain than a 12au7 as a pentode, maybe you meant 12ax7. but a triode strapped 6sj7 has a mu of 19, so that would be close. i've used the 6sj7 as a first gain stage in a diy SE guitar amp, and i believe the gain is around A=180 using a 220K plate load. I think I ended up using 150K load, and 1M/0.1uf feeding the screen for a little cleaner operation than the 50's fender circuits.
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