Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Fresh_Start on February 09, 2016, 02:31:36 pm
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I've attached a circuit snippet which I think follows the idea fleshed out by Geezer and others.
Original Thread (http://el34world.com/Forum/index.php?topic=4401.0)
More recent discussion (http://el34world.com/Forum/index.php?topic=4437.0)
I'm handicapped by lack of access to PC with ability to read SCH files, so I can't really see most of the drawings.
Snippet uses a triple throw/3 pole switch with on/off/on function.
The idea is that in one "On" position, the amp is virtually stock with a shared cathode resistor(s) net 250 ohms and bypass cap(s) net 30uf. Note that parallel bypass caps are grounded.
"Off" has separate 500 ohm resistors for each cathode and no bypass cap(s).
Opposite "On" position has separate 500 ohm resistors, each bypassed by a 15uf cap. There is a trim pot inside to adjust this "half" power position. Note that there is a virtual ground between the negative ends of the bypass caps.
Does what I have drawn work following Geezer's approach and HBP's explanation of how?
Would it make any sense to try this in a 5E3 circuit designed for home use only?
I get the idea that a Tweed Deluxe breaks up pretty fast, and most modifications seem to be geared toward increasing clean headroom - not cutting power from the amp.
Thanks for your thoughts,
Chip
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Look at page 3...
http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf)
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Look at page 3...
http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf)
Sorry, I should have mentioned looking at that repeatedly and carefully. That was the one drawing I can see full size right now.
The difference between that circuit and mine is that at full power, my cathodes share a common resistor/capacitor network.
Perhaps that difference is not worth pursuing. My research indicates that there is a difference in how the tubes interact and how much negative feedback is injected via the cathode when you have separate vs. common RC cathode networks. The original circuit was intended to reverse engineer a Carr power switch, and Carr apparently makes a point that some of their amps have shared RC networks for the power tubes while others have separate RC networks.
Whether or not that difference would be noticeable in the 5E3 circuit is unknown to me. Since my goal is to have a virtually stock 5E3 circuit at full power, I thought keeping the common cathode RC network might be worth figuring out.
Did I at least achieve my objective?
Respectfully,
Chip