Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mistersnitz on January 02, 2023, 02:34:21 pm
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I've posted this before but my thread got corrupted so here is my current layout and schematic for my single ended amp loosely based off of Uncle Doug's Tremo-Verb build.
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Have you built it?
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Layout... OT blue wire should connect to second filter cap.
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470k grid stoppers + 470k shared grid leak is wonky.
Look at 6V6 manufacturer info; the limit on grid circuit resistance in self bias is 0.5M per valve. You are 3x over that.
The facility to reduce bias to zero seems rather poor practice.
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Timbo I have not had the time to work on the project, hopefully soon. Also I wanted to get some feedback on the schematic and layout before starting anything.
Thanks Sluckey I will make the correction to the layout!
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No worries
The reason I ask is I'm not really into SE amps although I have built a parallel SE with a pair of 6GW8's and it sounded great.
SE amps have their greats but generally low wattage 5-10w
Haven't heard what a SE 20w would sound like.
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Haven't heard what a SE 20w would sound like.
fwiw, I've build a few in this range, the typical reply from the guitarist, that test drive for me;
"This thing is LOUD, this can't be a 20W amp"
most of mine are head-units through a 2 X12.
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2 parallel 6L6s?
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they ain't labeled
I get there with a single KT88, ~420vdc, dissipating ~42W, and ~60Vac ready to drive it, all the way to square-waves :icon_biggrin:
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they ain't labeled
I get there with a single KT88, ~420vdc, dissipating ~42W, and ~60Vac ready to drive it, all the way to square-waves :icon_biggrin:
Or 2 parallel 6L6GC fully driven with optimum efficiency
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With 300V B + 250V G2 a GU50 in SE is able to perform 18W
As datasheet you can refer also to the EL152 (civil version of the LS50/GU50 tube)
(https://i.imgur.com/Nm0MHAz.jpg)
A friend is building a 2 x GU50 in PSE amp
(https://i.imgur.com/p3VzEOo.jpg)
(https://i.imgur.com/Xm8iM1o.jpg)
Franco
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hello,
what will happen when V5 or V6 bias pot (2.5k) become a short ?
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Tubes will quickly die.
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I never tried but this seems a better way to have an adjustable Cathode Bias
Franco
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I never tried but this seems a better way to have an adjustable Cathode Bias
Franco
This looks like the ax84 layout. I have this in one of their SEL builds that I’ve tweaked into a more plexi preamp. It works very well. I had a bad tube that burnt up the original 2W pot and replaced with a 5W wirewound CTS pot a few years back. I believe it is 1K. I can bias anything from a 6V6 to a KT88.
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Bringing this back from the dead!
There's been some progress made, power supply and preamp turretboards are populated and soldered minus the flying leads and I've quickly mocked up the layout with the chassis to figure out placement of components. See attached pictures
I've made some (a lot of) modifications to the schematic and layout previously posted, I'll update when I start debugging and get closer to a final revision
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fwiw;
the OT might be problematic that close to the sensitive signals in the pre
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fwiw;
the OT might be problematic that close to the sensitive signals in the pre
Not much real estate to relocate the OT. If needed I can add a shield plate to create some separation, but unless I switch to a larger chassis that's where it's going to live for now.