Modified original post, added layout photos.
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5F6A Bassman total custom build - super low output
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1 ohm current sensing resistors in the power tube cathode returns would be very handy here.My band:- http://www.youtube.com/user/RedwingBand
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I just looked at the added layout drawings, and have a comment about the heater supply wiring. You can short out either of the 6.3VAC heater windings with that hum balance pot, since you have made a center-tap from the two windings, AND connected the wiper of that 500 ohm Hum Balance pot to that C/T. Removing the C/T Ground connection, leaving the two power tube heaters to run on each winding, then have the hum balance pot's wiper going to ground, it may work for the preamp tubes, but not for the power tubes. I think you need to re-think all that again.Logic is an organized way of going wrong with confidence
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With the preamp tubes in series I don't see the potential for improving hum with the balance control because there's no differential (I think that was conceded). And with the power tubes wired each to ground the 500R pot isn't a false CT, but a variable shunt that, at 250R per side, would probably need a gross adjustment to sink enough current to make a difference. Did I get this wrong?
And what was said above. It should be changed if for no other reason than it shouldn't be possible to dial in a dangerous failure.Last edited by Chuck H; 01-18-2018, 12:43 AM."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz
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The other thing I noticed is that you have one of the PI outputs going to the screen grid instead of control grid on your layout of the output section. Drawing error or build error?Last edited by The Dude; 01-18-2018, 11:41 PM."I took a photo of my ohm meter... It didn't help." Enzo 8/20/22
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Originally posted by The Dude View PostThe other thing I noticed is that you have one of the PI outputs going to the screen grid instead of control grid on your layout of the output section. Drawing error or build error?
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Originally posted by tomgilmartin View PostTrying to update my schematics. The schematic is wrong. I soldered the 2 xfmr leads together at the xfmr, never brought out the center tap. It really is wired as a fake center tap at the pot. Also, V1 V2 V3 are not in series. They are parallel from a true 12vac source."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz
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Originally posted by tomgilmartin View PostNot at home right now. That could be it! Will check in about an hour.
Waiting for cap discharge.
EDIT - I was agonizing over the layout of the bias circuit. At first I wanted to use the unused pin 6 on the power tubes, so while drawing the layout I kept moving the wires around. Got crossed up on pins 4 and 5. Drew it wrong, then wired it wrong. Hope I didn't destroy anything.Last edited by tomgilmartin; 01-18-2018, 01:38 AM.
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Originally posted by tomgilmartin View PostPower circuit early in the build.
[ATTACH=CONFIG]46611[/ATTACH]
Oh, and don't worry about the insomnia. Just a side effect of creative process.If it still won't get loud enough, it's probably broken. - Steve Conner
If the thing works, stop fixing it. - Enzo
We need more chaos in music, in art... I'm here to make it. - Justin Thomas
MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey
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Originally posted by Pedro Vecino View PostIs the secondary of the output transformer connected to ground?Originally posted by tomgilmartin View PostYes, at the feedback connection point near the presence pot.Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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