Tubes Asylum

What preamp? nt

76.90.100.230

Tre'

In Reply to: RE: Didn't get them...- posted by erik on December 19, 2023 at 16:12:35

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Have Fun and Enjoy the Music
"Still Working the Problem"

Follow Ups:

RE: What preamp? nt - erik 17:17:57 12/22/23 (2)
It's the Luxman cl-38uc. Got it lately. It has 3x12ax7 for the phono and 5x12au7 for other purposes. I don't remember any contemporary preamps with so many 12au7's. The stock tubes are from JJ, I never liked their miniature preamp tubes. Freaking NOS prices are unbelievably high.
- RE: What preamp? nt - Tre' 19:32:55 12/22/23 (1)
  The 12au7 is not linear enough to use without a ton of feedback. They do fine in a cathode follower stage (buffer stage) because of all the local current feedback but as a gain stage tube....no.
  The 6cg7 is very linear (just like the 6sn7) and is a great replacement for the 12au7. You have to rewire heater connections on the tube socket and the heater supply has to be able to do 600ma of 6.3 volts vs the 300ma that the 12au7 draws. Otherwise a 6cg7 will be perfectly happy in a circuit designed for a 12au7, there will just be a lot less harmonic distortion.
  All 5 triodes per channel (2 1/2 tubes, 5 12au7s total) are involved with gain stages. I think the power supply will have trouble with the heater current draw doubling. 3 amps vs. 1.5 amps. So the power supply would have to be modified.
  I will never understand why designers use this tube in gain stages.
  Tre'
  Have Fun and Enjoy the Music
  "Still Working the Problem"
  
  Edits: 12/22/23 12/22/23
  - RE: What preamp? nt - erik 20:54:12 12/22/23 (0)
    I was told that two tubes on the left are for its tone controls, so only 3 tubes involved with gain stages. The encapsulated ones are for the phono. Got it mostly for the tone controls, and they're good. Basically it's a hybrid. No tube rectifier or voltage regulator.

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