Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dscottguitars on March 29, 2014, 05:21:19 pm
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Hi, I'm almost done with this new version. I'm waiting for the screen filter cap to come in the mail. Here is a schematic and pics which the last one is the first one of these. I increased the chassis size from 8x14x2 inches to 9x16x3 inches. That makes a big difference in getting a cleaner wiring scheme. I have quite a bit going on in this amp, high/low power switch, tube rectifier switch and fixed/cathode bias switch. This one uses only one channel but still has a distortion/clean signal path (that I hope works!)
I tried to keep this as clean as possible and hope I'm not overlooking anything that could cause some noise issues.
Let me know if you spot something.
Thanks,
Daniel
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Needed to do two posts for the schematic and older amp pic.
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Much better!
Like you said you do have a lot going on in that amp. So pretty much no matter what you do it wont be as neat as a simpler amp.
Brad :icon_biggrin:
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Your first version remember me some II WW apparatus that I dismantled
really very complex circuits in small space
Using a larger chassis you have chosen the right path
K
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Thanks guys,
I'm hoping for a quiet amp. I'm still waiting for the screen filter cap though. I have some 450v ones but usually I have 465v+ on the screens. Is that too much for those caps?
Daniel
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Yes it is
465V B+ vs 450V caps won and kill caps
if correctly rated caps are missing you can use a pair of 300v caps in series (don't forget the paralleled resistor) and you obtain a 600V cap (1/2 of the capacitance)
K
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Hi, & thank you for pics-you got more than a few hrs. invested in there, huh?. Congratulations on getting all that in there. Definitely a good step enlarging chassis. En regards to chassis, how is finished piece (looks like one I made myself) performing? Mine had some structural and squeak issues when added to cabinet and cranked up.
I'm wondering about heat issues, with caps & large ceramics in such close proximity. Also, ceramics next to each other, maybe spread out-staggered more?,...on first pic, wire looks close to lg. cer. CR on left side.
I only mention because I'm running into problems with electro's & heat in amps, computers, even flat screen in house.
Look/Listen forward to soundclips.....any speaker choice, or cabinet in mind, as it looks like maybe a stand alone amp head or?.
Either way, I'm envious of your finished pieces. Seems I get them to where I can hear them, and If not the best I think they can be, start tearing down, and rebuilding.....Great site, huh? I don't think I'd have built amp 1 without this 'place'.
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The two white cement resistors next to each other only get used one at a time, the high/low power switch chooses between those two, so having them close is good for heat dissipation like a heat sink. The other one on the left with that wire shouldn't be a problem, the wire won't get that hot. It's not touching even though it looks like it and I'll move it over towards the caps. Thanks for the observation. I've never had any squeak issues mounting it in the cabinet. I use four long 1/4-20 bolts near the corners bolted to a 3/4" piece of hardwood. The speaker cab I have has a Jensen Neo 12" and a Celestion Vintage 30 that I can switch speakers or run both for 4 ohms.
I may need to change that Mallory 450v cap in the first amp, my nephew has it. So far so good for now.