Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on February 24, 2020, 01:00:41 pm
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Voltage on 6V6 Plexi seems high, it's the PT from an AO-43 chassis. I get 425v on B+, GZ34, gives me 420v on plates of USA 6V6GTs. Am l going to toast these nice tubes? Bias is at 23mA, matched set within 3 mA, biased at 70%. The GZ34 GT says made in Britain but has the GE dots and logo, says Electronic Tube.
I could put a 5v4 or 5U4. The PT seems to handle 6L6's too not hot at all but same rectifier tube, B+ drops to 400, I understand it's a different draw.
Am l going toast the USA 6V6s? I don't recall that high B+ from these PTs, I had a Sovtek 5Ar4 in their before l came across this GZ34, both read the he same B+
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my poor memory seems to think north of 400 for organ donors was "normal". lots of examples of 6V6 running >400vdc. The nature of guitar tube amps seems to be "accept" PA tube changes as the cost of doing business :icon_biggrin:
or buy a set of JJs, save those for a 5W audio design that keeps them alive for years
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Plenty of pp fixed bias 6V6 amps were running 420V on the plates back in the '60s when all you could find were USA tubes.
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_ab763.pdf
https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_aa1164.pdf
Besides, voltage (within reason) doesn't kill tubes. Current does. I never worried about 420V on my TDR or 6V6Plexi. That AO-43 iron is perfect for those amps.
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Yup, the DR has 330-0-330, same as the AO43, same plate voltage as l get too, and nothing but USA tubes at the time. Same with the Princeton too, it has. 340-0-340 PT, uses a 5u4 so a little less plate voltage. If it's the current that kills the tubes, l'll just keep the bias at 70%. I was just blown away at the versatility of the 6V6 Plexi, this little beast is a classic rock machine, not one player didn't like my conversion, that's why l'm doing 5 or 6 of the these, I have ten AO-43s. Four are promised to some of my friends kids. it's a ton of working converting these chassis's (unless you builds a rats next like the first one I did) but l like doing it, especially now that l'm paying a lot more attention to neatness. Wish l could figure out how to get a nice layout from my hand drawn one like you guys do, l'm ok with the faceplate program but the layouts are a little more complicated, if I sell one of these Plexi's on Reverb, any objections to sending the buyer a schematic l got here?
Might have to sell one to buy more parts to finish the rest. I want to do a November, I bet that amp sounds nice too.
I'd like to know who came up with idea of making the first 6v6 JMP Marshall 1987, l know they came about around 1965 and a copy of a Fender Bassman by Jim Marshall, except the first gain stage is biased totally different, the plate voltages on that first 12ax7, are at least 50v difference, blending them is awesome, so who was the guy, Huss...?
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I'd like to know who came up with idea of making the first 6v6 JMP Marshall 1987
Mark Huss did the first one I ever saw. I basically copied his schematic with a few adaptations. The November amp is fine too, but I prefer the 6V6Plexi. They both share the same preamp and there are only minor component value differences in the PI/PA. I bet your board layout would work for a November.
if I sell one of these Plexi's on Reverb, any objections to sending the buyer a schematic l got here?
I don't have any objections. Can't say about Doug's version. Just a suggestion, post a link to the documents files in your Reverb listing rather than providing the buyer with a file. Might even help you sell. 'course the layout may be pretty useless unless your layout is identical and I doubt it is since you are using that narrow chassis.
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Yeah, it ain't. I'll have to take time to figure out that program, lots of info here on it. Thanks for all your help.