Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: AmberB on July 24, 2021, 03:33:26 pm
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Other than the availability issue, is there a reason why the EL84 is preferred over the 6GK6?
I started looking at the 6GK6 because someone mentioned it as a replacement tube for the 6GW8 on the Bogan CHB-20A in an older thread on the forum. Obviously, you would need another dual triode tube as well to replace the triode section of the 6GW8. What was said was that if it became difficult or impossible to get the 6GW8, the 6GK6 would work in it's place with a bit of rewiring of the circuits involved.
Upon looking up the specs for the 6GK6, it seems to be very similar to the specs of the EL84, more or less the same heater current, almost the same output transformer impedance, close enough to use the same OT for either tube, and the 6GK6 has a slightly higher max plate and screen voltage rating.
I know that the EL84 became popular because of British amps like the Vox, but it seems like the 6GK6 is at least as good of a power tube.
Any opinions on this?
PS, I found a bag with about 20 of them in my tube stash...
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I've found the only "real" way to know, build it n see, well listen! As a tech, i like scopes n numbers, my ears are useless :icon_biggrin:
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…the 6GK6 has a slightly higher max plate and screen voltage rating ...
That may be due to ghe valve types being rated under different systems. ie EL84 / 6BQ5 design centre, 6GK6 design maximum.
Design max ratings are intended to have a suitable derating applied by the equipment designer, whereas design centre can be used directly, no derating required.
https://frank.pocnet.net/sheets/135/6/6GK6.pdf
https://frank.pocnet.net/sheets/093/6/6BQ5.pdf
RCA Application Note 174 explains rating systems and introduces the design max system -
http://www.one-electron.com/Archives/RCA/RCA-AppNotes/RCA%201958%20AN-174%20Design-Maximum%20System%20for%20Rating%20Electron%20Tubes.pdf
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Well, from what I see based on those GE tube spec sheets linked in the previous post, if you give either tube 300 volts to the plate, and an 8K load push-pull, they're just about identical in output rating and distortion rating. They're obviously not a direct replacement tube, but with a change of tube socket and wiring to the tube socket, either will do the same job.