Tubes Asylum

5814 instead of 12au7 - loud noise

72.74.123.24

erik

Folks, got a brand new set of RCA Command 5814a tubes for my Luxman cl-38uc, which uses the 12au7 variant, 5 of them actually. Now, with the 5814 I get very loud hum from both channels.
Is it possible that the 5814 variant is not compatible with this particular circuit or the tubes are simply bad (unlikely) ?
Thanks

Edits: 02/05/24

Follow Ups:

RE: 5814 instead of 12au7 - loud noise - f1jim@yahoo.com 15:08:22 02/07/24 (1)
The 5814's should work just fine. Sounds like you got a bad tube if the originals work fine. Their are very few pieces of audio gear that are built with power supplies unable to cope with the difference in tube requirements for this application. In fact, I have never heard of a case.
Too bad you sent the tubes back already. It would have been interesting to swap them out individually to find the culprit tube.
f1jim
- RE: 5814 instead of 12au7 - loud noise - erik 18:24:16 02/07/24 (0)
  The originals were JJs, crappy sound, but completely silent, then I got a quintet of Gold Lions, again silent, and finally got a set of Valvos made by Amperex - no noise whatsoever. I think I'm gonna stop for now until I find something really interesting. Unnecessary abuse of the sockets is silly.
When you put the original tubes back in, is it quiet? - Chip647 08:51:03 02/06/24 (1)
Try replacing the tubes one by one to find the position that is causing problems. The 5814 draws a tiny bit more heater current but are otherwise identical electrically.. 5 tubes (10 line-stage tube sections) will have 2 "SRPP" circuits per channel plus a single tube section cathode follower. So only that one common tube with the 2cathode followers would spread noise to both channels unless all the tubes are faulty.

If the preamp still has noise with the old tubes, it is likely when you removed the tubes one of the plastic PC board connectors got jostled or a solder connection got broken.
- RE: When you put the original tubes back in, is it quiet? - erik 10:29:34 02/06/24 (0)
  Thanks Chip, but I already sent back the tubes. The preamp is absolutely silent with the Valvo/Amperex set, which I acquired recently, actually I'm thinking about getting one more set just in case.
RE: 5814 instead of 12au7 - loud noise - opalize 09:20:30 02/05/24 (1)
The 5814A is not a direct sub for a 12AU7 because the heater current differs. I wouldn't rule out a possible bad tube, however. Do you have any other circuits within which to try your 5814A? Also consider cleaning the pins and re-trying.
- RE: 5814 instead of 12au7 - loud noise - erik 10:35:38 02/05/24 (0)
  I think the pins are good, perfectly clean, at least visually. A few weeks back got a new set of Amperexes, again with regular (not gold-plated) pins, and they were absolutely quiet.
  
  Do you think I can damage the unit while trying to determine the bad tube (if any)?

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