Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: waldner on August 25, 2017, 10:07:23 pm
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Hey Guys! It's been awhile but I'm back and looking to build another amp. I've successfully built a GA5, 18 Watt Stout, 5E3, Bassman and a Ceriatone DZ30, but don't know how to read or understand schematics. I rely completely on building from layouts.
I'd like to build a Hoffman Princeton Reverb but do a version that uses 6L6s and could play louder and stay cleaner longer to gig with. I am hoping someone could help me figure out what to change from Doug's layout and which transformers to get for a good working version. Any help would be greatly appreciated.
Thanks!
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What you describe is Hoffman's single channel AB763. Take a look.
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princeton rev. uses concertina for PI. AB763 is long tail PI - princeton rev. has more gain in preamp path. also, princeton rev. is prone to blocking distortion. AB763 is smoother. a single channel 50W AB763 is what you probably want.
use bassman 5F6-A / super reverb power transformer & output transformer. use super reverb choke.
use hoffman part number Mojo762 for PT
use hoffman part number 022855 for OT - has 2 ohm tap only. use hammond 1760K or use Mojo774 for OT with 2/4/8 ohm taps.
use hoffman part number 125C1A for the choke - this is the large fender choke.
--pete
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So it sounds like the Princeton and the single channel AB763 are similar but not quite the same. When I look at the two layouts I see that the AB763 has an additional tube and a mid control as well as the differences that Pete mentions.
I kind of like the idea of the building the more simple Princeton if possible. Are you saying I can just build that and change the PT, OT and Choke and leave everything else the same and use 6L6s? Have it not be quite as clean and powerful as an AB763 but go a little louder and a little cleaner than the stock Princeton 6V6 version?
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Are you saying I can just build that and change the PT, OT and Choke and leave everything else the same and use 6L6s? Have it not be quite as clean and powerful as an AB763 but go a little louder and a little cleaner than the stock Princeton 6V6 version?
yes
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Ok, I'm about to pull the trigger on ordering all of the parts for my slightly more powerful Princeton Reverb (6L6) build. I like the idea of using Hoffman's layout and ordering everything from Doug other than the PT, OT and Choke. Can anyone recommend which transformers I should use to run 6L6 tubes. I was thinking about getting Classic Tone? Do I just order all of the Deluxe size transformers? Like these:
40-18002 Output, 20W - 6.6K to 8 Ohms 125A1A, 022640, 041318
40-18016 Power, 20W, 120V 125P23B, 125P23D, 025130
40-18040 Choke, 50mA DC, 4 Hy 125C3A, 022707
Any recommendations would be great.
Thanks.
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You need to upgrade all iron to suit a 6L6 amp such as Bandmaster, Tremolux, etc. I would use these...
OT - 40-18006 - 4K:4,8,16Ω
PT - 40-18042 - 40-18041
Choke - 40-18003 - 4H, 90mA
This PT will probably not fit a stock Princeton Reverb PT cutout.
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I am not as experienced as some of you on this forum, but wouldn't the 40-18042 transformer be overkill for two 6L6s? It is rated at 690/640VCT@450mA, which is more in the 80-100watt range.
Mike
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but wouldn't the 40-18042 transformer be overkill for two 6L6s?
Absolutely! I wrote the wrong number. Should be 40-18041. Thanks for catching that.
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I used a David Allen TP25 power transformer in my Princeton Reverb which fit into the stock chassis cutout with no problems. It's made by Heyboer and you can run 6L6 or EL34's with it. And I would say with the above mentioned OT 40-18006 it would be loud as heck.
Having built a single channel AB763 Deluxe Reverb, I would be inclined to recommend a single channel AB763, like Pete said, as a better alternative. But the Princeton is pretty good too if you are planning on using a PR chassis. I made my own chassis for the SC DR.