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In Reply to: RE: 6C33C tubes posted by unclestu on March 06, 2014 at 18:24:07
I built a 6C33 amp in ~2006, though I used decent sockets in the build.
I have been using the same pair of 6C33's since then, and they are still within 5% of factory specs.
The bias does wander a little bit, but 2mA of wandering on 200mA of idle current seems acceptable to me.
Follow Ups:
Interesting:
how do your test them ?
I do notice once you find a good set, they seem to last a very long time. The pins on the 6C33 are rather small and they have to handle a lot of current. Some tubes had had a weird scale which needed a lot of manual cleaning (read sandpaper) t0 clean up.
The Chinese made sockets have such crappy metal that the spring tension weakens noticeably over a short time. Flip the amp over and the tubes will simply fall out. I've had to change sockets on several amps. On one animal, the weak tension caused arcing at the connection and eventually it simply ate away at the metal and there was simply a hole where the contact patch was supposed to be. Should have kept the socket or taken pics....
I test them in the circuit, looking at several operating points that I can dial in with the fixed bias setup (the B+ rails are pretty stiff, so I can get a spread and compare them against where they should be on the published curves.
Yeah, the Chinese sockets that have the black piece of steel acting as a clamp are the worst creations ever. Often times, those clamps just snap off and will rattle around in your amplifier.
I've had the same experience with this tube as CB has said (same pair since 2008).
I do normal pin cleaning every blue moon and never had an issue (really nice to have on a desktop during a cold winter).
To the OP, I tried all the different variations, and kinda settled on the ones with the winged Y (usually for the 70's).
The sound is ultra close and those tubes are tough to find now (in other words, don't bother).
Rumor has it that when these tubes were in full production that there were 40,000 a month being made. So even if that was just a year,..
My Audio Mirrior 45 Watt SETs run a pair per monoblock, and I am impressed with how long they last. But I'd like to have some at the ready for when they do crap out to avoid scrambling and minimize down time.
I just picked them up from one of the eastern block sellers on eBay. It's been a while.
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The best test is to apply heater volts to one half of the heater at a time . Not really worth testing on a valve tester , better off building a dedicated rig . I used a 10H PSU choke as load and tested them this way
Al
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