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I seem to have noise issues with a couple of long black plate RCA 12AX7s.
I have seem to remember reading that they were prone to noise. Is this something I have made up or is there evidence of this? They were purchased from a reputable dealer and used in a McIntosh MX110 and also an MC240.
I have tried RCA long grey plate 12ax7s and honestly can't really tell much of a difference between the two.
Has anybody compared these issues with these tubes and also, is there that great a difference others are hearing between these two colours?
Thank you in advance - I do love the sound they give in this amp.
Paul
Follow Ups:
Excellent tube, maybe my favorite 12AX7. While I have no experience with the RCA gray plates, I've used quite a few of the long black plates, mid-'50s vintage, and never found them particularly noisy.
I've never had noise problems with RCA blackplates as input tubes in my Rogue amp. Don't remember reading that they were prone to noise either.
If you are using them in a phono circuit, they should be screened for low noise. That would be true of any tubes you would use in that circuit.
Are these tubes new - meaning not used yet?
I had a similar issue with a noisy tube in a position. The oddity was that with 20 plus hours of burn in the noise/hum disappeared. And it was a 12AX7 tube.
Can you put this tube in another position?
Can you try rolling in one at a time?
If the original tube is not shielded I doubt that is the problem.
post your findings.
charles
Tube is in the 3rd amp position - (There are only 3 12ax7s in the MX110 - the phono section for two of them and also this position) so to be honest the only other position to put that tube would be in one of the cathode follower positions (now have grey plates in there) of the MC240.
I have had this tube in the MX110 for the better part of a year with no issues - have checked each tube in the audio path in the 110 and it's this one that is the noisy one - tests really well on my Stark 9-66 (just calibrated) and it's kinda confusing about this...
I have put in another black plate in this position and it's fine.
Just really puzzling about it and another BP went howling about a year ago - that was during burn-in.
This isn't.
Paul
I have used quite a few BP RCA 12AX7. But these days, good ones are hard to find. I supposed that many being sold now are noisy, microphonic or something or other. I have had better luck with GP RCA 7025. You can still find high testing, low-noise ones
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