Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: idsnowdog on February 03, 2024, 10:11:14 am
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I am finishing up a 5E3 build that I bought half completed. It has a choke but I'm unsure where I would connect it? I have used the values in the board layout. What components would need to change?
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Replace the 5K/5W resistor with the choke.
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OK, I'll ask...Are you SURE you want a choke there?
That 5k resistor is an essential part of the tweed deluxe sound. Substituting a choke will result in a significant increase in voltage on the power tube screens, PI, and Preamp. I have no formal electronics training but suspect that power amp bias will also be changed on an amp that is already running at the limits. Hopefully some of the real knowledgeable folks here can advise on that.
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It could go either way. The chassis is already drilled and a choke is already there. There's also an adjustable bias circuit that can be hooked up if necessary. I intend to take this to a tech for them to check out and apply the finishing touches. I will tell them to choose whatever works and sounds the best.
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...There's also an adjustable bias circuit that can be hooked up if necessary. I intend to take this to a tech for them to check out and apply the finishing touches. I will tell them to choose whatever works and sounds the best.
Is that is a Fixed (negative voltage on the grids) bias circuit? The 5E3 is Cathode biased. With the choke and fixed bias, the amp could still sound good, but probably not like a stock 5E3. Maybe the tech can let you play it both ways to see what you like best. :icon_biggrin:
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Early this fall I bought three unfinished Hoffman project amplifiers for cheap off Craigslist. One was an AB763 that was about 80% complete, one was a 5E3 variant about 60% complete, and one was a "Harvard" variant about 40% complete. I believe the previous owner ran into problems while building them and abandoned them.
The AB763 was built on the chassis of an ELK Pro-Sonic, and the control layout was backward from a Deluxe Reverb so wires were crisscrossed to compensate, and were a bit messy. The AB763 was also missing its tremolo driver so I drilled another socket reversed the front panel layout to match the board layout and finished it up.
I couldn't decipher what was going on with the 5E3 because it didn't match any schematic I had seen. So I stripped half of the components and rewired them to match the 5E3 layout. I left the choke and the bias board alone since I can't prove or disprove if they work. It also has a 6AX5 rectifier because I believe the transformer lacks a 5V tap. I figured I would let a tech decide if they can be used.
The "Harvard" was also some form of Deluxe variant that I couldn't decipher. The only thing that made it a Harvard was the tube compliment. That one lacked a tube rectifier and had solid-state rectification instead. I completely scrapped that board and built a Harvard using the same components. Once again it was drilled for a choke but it didn't come with one so I used one I had on hand. I will let the tech decide if there's any advantage to using it.
So, I am pretty much painting by numbers and trying to match the layouts of all three while making a few tweaks. I would think if I have the majority of components in the right places and if the previous owner's choice of transformers was correct I might get at least one usable amp.
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Did you buy them all from the same person?
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Yes, he said he was getting out of building amps. I haven't kept in touch because I didn't want him to feel he wasn't obligated to be my tech support.