Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ncusack on May 26, 2015, 11:06:52 am
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Hey All,
I'm wondering if anyone has experience doing a cathode bias 6v6 amp running ~400VDC B+ and a 6.6K primary for the output transformer?
I'm looking at building a single channel deluxe style amp and the PT I have will put out about 400-420VDC for the first B+ node and I have a hammond 1750H deluxe reverb transformer im looking to use with it. A lot of what I've read about cathode bias 6v6 is an 8k or higher primary should be used but I'm curious if the lower primary can still work.
Any info would be a great help.
Regards,
Neill
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Try searching this forum for "cathode biasing" should be a treasure of info. Most of my builds are Cathode biased. I find what "everyone else" used for the bias R, then adjust as needed. With a PP amp you probably wanna start around 60 - 70% max plate. I also keep a box of 10watters for jumping in and out. a good range would be 100 to 500 ohms. For initial setup I like using 1 R per tube. That gives me a good idea of tube matching.
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Are you more interested in maximizing the output power or the best sound? The load matching requirement for them are not necessarily the same.
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> ~400VDC B+ and a 6.6K
That's not a happy fit for 6V6.
Though I do believe many of the late Fender 2x6V6 amps ran similar.
It is a happy fit for any of the bigger tubes. I had a too-LOUD Ampeg with 6.6K load and a burnt 580VDC PT, I rigged it with 400V B+ for 20 Watt output and could run 6L6 EL34 7027 6550 KT88 cathode-bias with no adjustment.
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But if you turned it into a fixed bias output stage and biased the 6V6s at 60%-70% it should sound pretty good. I suggest using a 6G3-type LTP to drive these and an inverting stage at the start with a TB tone stack and a vol pot following, and another inverting stage as the recovery stage before the PI. Should get a pretty nice sound