Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: MonoPoly on July 15, 2020, 08:32:17 pm
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Hi, I'm a first time amp builder building a Hoffman ab763 deluxe reverb, largely using a lot of salvaged old parts (including hammond chassis) to keep the cost down. Using the chassis, I have had to tweak the layout quite a bit, and I'm not sure if I have a way around the center tap from the OT crossing the path of an AC line (whether it's the heaters or the lines going to the rectifier). Instinctively, I feel like this is a bad thing. Is it? How bad? If I have no way around this, what can I do to reduce hum? I don't need to be insane about keeping the noise floor down -- I'm planning for this amp to be my bar gig amp. I have some smaller amps that suit my needs for recording and quiet listening audiences.
Secondly, I've picked up a lot of little crumbs about what to consider with layout, but can anyone recommend any literature that is fairly encompassing?
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Instinctively, I feel like this is a bad thing. Is it? How bad?
Not a problem.
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Thanks! That was quick.
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Secondly, I've picked up a lot of little crumbs about what to consider with layout, but can anyone recommend any literature that is fairly encompassing?
My bar amp is also a hammond conversion. Other guitarists ask a lot of questions and its fun to answer them!
Which one did you use the parts from? As far as layout, try to mimic a fender layout or something like Doug's done: https://el34world.com/Hoffman/AB763Project.htm (https://el34world.com/Hoffman/AB763Project.htm)
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I'm using a chassis, preamp tube sockets, and some wiring from the early version of a PR40. I'm trying out the OT and reverb driver as well. The impedance for the OT is ballpark, but it seems like it might lack lowend, which I might actually like (as a mix engineer I almost always cut some lows out of guitar). I did some math, and it looks like the reverb driver matches the ab763 circuit with a vintage accutronics 4fb2c1b tank (higher input impedance, slightly shorter decay, but otherwise same as standard DR tank). I picked up the tank and pr40 preamp/output chassis (without tubes) for $20. I initially was going to use a standard DR chassis, but found out that the DR cabinet I bought from a friend a year ago was actually a couple inches narrower than a DR cabinet (it was $60 and came with a 60s Utah alnico speaker, so I can't complain). Had I known that the cabinet was narrower before I bought the turret board, I probably would have opted for a 1 channel short board version minus trem and made something that looks a lot cleaner inside.
Here's a photo of where I'm currently at. I threw in a few things that aren't mounted yet. Yes, that's a piece of a license plate.