Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jordan86 on April 29, 2023, 11:45:21 am
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Thinking of a cathode biased 6v6 Plexi style build in the Hoffman/Huss/November vein of things...Shopping OT's and curious to get some feedback from guys who have walked this before. Not I am a chronic over thinker and researcher. :icon_biggrin:
Considering all the standard (Mojo, Hammond, etc) options in the Marshall 18 watt OT, the tweed deluxe OT, 15w Princeton OT, 20w Blackface Deluxe OT, or possibly this 30W JTM30 OT (https://www.hammfg.com/files/parts/pdf/1750NA.pdf)
1) Any personal experience from you guys on ~6K vs ~8K primary? I'll be using a solid state rectifier running about 390v on the 6v6 plate fwiw.
2) Curious if an undersized OT would give up the goods quicker? I will have strong filtering and 270ex PT which has more than enough power. Or do plexi's do better with an slightly oversized OT.
3) I'm VERY curious to possibly run 6K6's. (May possibly need to go tube rec with a 5y3). As those usually are around 12K plate resistance, the 6K OT seems a better choice, and then I can just compensate by using the "incorrect" speaker out to double the reflected load.
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this was my last build, got it working with 6K6's, played about a week, then re-built as 6V6. Used the speaker to set reflected power.
both tubes gave ~~~~~ the same "sound", the 6V6s would handle OD a smidge better, produced a "fuller" sound. The Mrs.'s didn't like the LOUD from either tube set :icon_biggrin:
the OT is an EDCOR
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Shooter, how did the tremolo work out in that amp?
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worked good at bedroom volumes, nice "effect", got lost once you brought the volume up past ~~7. I kept dinking, but the tradeoff was less amp power for more trem. I disabled it when I went to 6V6 and re-adjusted the voltage divider feeding the PI so I could get a bigger drive signal to the PA.
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All things equal, and 6.6K OT would produce more wattage than an 8K one, correct? Would a 15W saturate/compress more? I know that's a personal preference thing, but anyone found that compression to be desirable? Or is that less "plexi" like?
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i'm just a tech, you'll have to wait on the guitarists
a self biased amp, by "design" wants to operate class A, even with p-p, it still likes class A, odd things happen when you drive it hard into A/B
so things like transformer saturation, sagging supplies produce un-intended outcomes, sometimes good, like a single tube champ being beat into submission.
I would recommend keeping it within +/-20% of Max clean at the speaker, then use pedals to "create" your sound, let the amp do it's thing and make that sound louder, with simple "spices" added in from the Amp itself