Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ALBATROS1234 on December 25, 2019, 08:47:32 pm
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been playing around in the lab , bought some tube lots some time ago and occasionally i experiment with oddball tubes.tv tubes are great, horizontal/vertical deflection tubes are beam power tubes. i found a few of the above mentioned and noticed they have the same pinout as a 6L6 except pin 3 is no connection and the plate connection is a post on top. they handle 600v max plate voltage. granted they suck up 1.2a on the filament. but i stuck them in my single ended 6L6 amp and clipped a double alligator cable from pin 3 on the underside of the tube socket to the top plate post and these bad boys sound every bit as good as old u.s. made 6L6gc types and 5881s. very similar in everyway, they do have a 11 watt max plate dissipation closer to 6v6 territory but sound just like a 6L6gc in side by side testing. i have 3 of them and all screamed in my amp with 5k primary ot and close to 305v on the plate. just wanted to mention this to any who like to play with odd tubes, these sound great on a guitar amp.
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just saying because they are like $3 to $5 nos on ebay and they sound killer. its not a desireable tube but has desireable tonal qualities. like so many other oddball tubes. fortunately for people like me who arent limited to fender deluxe schematics there is a whole world of unloved tubes waiting for their day to conduct current again and make guys like me happy with tonal texture for days. i just report my findings with the hopes that someone else might make some undesirable tubes sing again. cheers.
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careful. you can burn up the screens on those HO tubes quick. most have a 250V or less max rating. vertical sweep tubes work better for the most part. 6DC6GA were remarked as 7867 and tung-sol published data for audio use. i built push-pull amps with 6JB6 and 6CD6GA/7867
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macintosh built a hifi amp with 6BG6 which are a sweep rated 6L6GA. good stuff.
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6CM5 and 6DQ6 are great as well.
https://www.ozvalveamps.org/goldentone.html
https://www.ozvalveamps.org/playmaster.html
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Thanks for posting this info. I've got a stash of 6BQ6 somewhere. Looked up the data on them and was wondering at the time if they would be good candidates for some of this big organ iron that I have that is somewhat high voltage for your typical setup and have gobs of current available for filaments.
Did you try them wired for triode and pentode operation? Seems I read it was worth a try to wire with a switch to go back and forth with nice tonal variation between the two modes.
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http://retrovox.addr.com/40WPM116.pdf (http://retrovox.addr.com/40WPM116.pdf)
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see also attached 6dq6a documentation
Franco
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fwiw
you probably found this data, but if not, I cutnpasted from a couple discussions;
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Did you try them wired for triode and pentode operation? Seems I read it was worth a try to wire with a switch to go back and forth with nice tonal variation between the two modes.
i highly recommend NOT doing that. again, screen voltage ratings are not like that of audio pentodes: HO pentodes screens have a much lower operating conditions as in the G2 slope of the HO pentodes is MUCH steeper - IOW, typical useable transconductance is achieved with much lower screen voltages. so unless you're running HO pentode anode voltages around the screen ratings, then connecting them as a triode would not be wise.
--pete
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thanks guys, glad to see theres more mad tube scientists. blue heron, i just ran it tradional pentode mode not in triode. i saw the 250v screen max. this is why i used a variac ala eddie van halen to reduce my screen voltage. i got it around 260vdc with plates at 305vdc. i find power tubes that suck alot of filament current usually suck alot of current in general even at the moderate voltages i was a 100% plate dissipation so it would have to be biased differently in an operational amp. i was just impressed by the tone sounding so much like an old usa sylvania 6L6gc and thought i mught pass it on. thanks for the schematics, i know i have some 6dq6s as well.