Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => PC Express and JSchem - Schematics and Layout diagrams => Topic started by: tubenit on June 07, 2011, 11:42:25 am
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Here you go Chip, you can use this to edit etc.... into your idea
I "boxed" up a triode/CF, 5879, Marshall tone stack & a triode
Change the pin #'s on the concertina and power tubes to reflect 6BM8 triodes and pentodes.
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Here is a VERY rough draft of the circuit I had in mind. tubenit was kind enough to assemble the bits & pieces I needed in an SCH file, so I thought the least I could do was pull together the basic concept for "Chip's Doodle".
I want to replace the guts of my Blues Junior with something quite different - using a 5879 pentode in the preamp. The only problem with the designs tubenit & Geezer have worked out and shared with us is too many knobs. From all of the discussions, it seems important to be able to control both the input level and the output level from the pentode stage. This is a single-channel solution which may work (and may not). I don't know if the cathode follower makes sense where it is, but my thought was to smack the pentode despite having the TMB tone stack in front of it.
The power amp is mostly based on Gibson's GA-8T. A long-tailed-pair PI may turn out to be a better choice. If so, I'll use Geezer's Little Wing power amp design. The NFB is another wild ___ guess and I'll have to put it on a trim pot to figure out whether or not it's even beneficial.
The power rail resistor values are a stab in the dark at this point.
Please note that there are TWO sheets in the SCH file, one for the preamp and the other for the poweramp. It just got too tight on one page.
Cheers,
Chip
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Just another thought. I split a dual triode around my 5879 in my TOS.
With respect, Tubenit
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Just another thought. I split a dual triode around my 5879 in my TOS.
With respect, Tubenit
I like that thought too! Do you think it's a mistake to have the TMB tone stack before the pentode?
Chip
P.S. I've updated the schematic & parts of the first post.
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Do you think it's a mistake to have the TMB tone stack before the pentode?
I would lean towards having the tone stack follow the CF. So, if the CF is prior to the pentode, I'd have the tone stack follow the CF prior to the pentode. If the CF follows the pentode, then I'd have it follow the pentode.
Hope that makes sense?
With respect, Tubenit
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Makes complete sense. It already had occurred to me that a MOSFET cathode follower between the first gain stage and the tone stack would let me put the triode CF after the pentode. That would result in the natural compression from the CF coming after the pentode. IIRC you reported the best results with that. My concern is what impact the CF would have on the reverb circuit and the PI - heck, it might be beneficial to have more current going into the 1-tube reverb...
Thanks again for your thoughts and help.
Chip