[mclaren]

Hi Jim

Following your advice I purchased 2 more 12AU7's and changed the tubes over one at a time to see if there was any improvement. With both tubes replaced the noise problem still remains (in both channels). The original 12AU7's were EI Gold Elites, as were the replacements.

I note your reply to another Clarinet owner back in February with the same problem - "Squealing would be second tube. Caused by the high cathode to heater dc voltage (well within spec). Marginal tubes will squeal in this mode. Needs very good cathode insulation".

You seem to be suggesting better quality 12AU7's are needed to solve this noise issue, the EI's appearing to be marginal tubes. If so can you please offer some ideas on possible replacements? Is there any advantage to replacing both 12AU7's with a matched pair?

Mike

[hagtech]

I haven't had any squealing with the Sovteks - er, ElectroHarmonix.  Nor any NOS.  Usually the quality of NOS materials is superior because of quality controls and mass production.  Back during the cold war the conductors and insulators used in tubes were in high production by many companies in serious competition. 

The tubes do not have to be matched.  But it helps to have them somewhat close to maintain good channel balance.  You can mix and match brands.

jh

[Eric H]

I had trouble with "whistling" (microphonics) with my Clarinet/Cornet2 combo in its early days.  Eventually I found a set of tubes that worked, and later I found Jim's advice that the second 12au7 on the Clarinet is the critical tube to be true.  However, I never tested to the point where I could say that "tube A squeals, tube B doesn't" and I suspect from my experience that slightly microphonic tubes in other positions might also contribute to the problem...    Anyway, I sorted that out long ago and have been happily listening ever since.  Fwiw, the 12au7 I have in the second position on my Clarinet is an RFT ECC82.  I'm pretty sure I got that from Jim McShane.  Also, I did a buy a couple each of those gold pin EI's as well as some JJ's.  I don't claim to have done definitive testing but none of those tubes are in my system now - turns out the three 12au7's in my system were all NOS purchases, so there's a data point for you.  Good luck, you'll sort it out and be happy 

[PatOMalley]

I have had issues with noisy 12AU7's. The RCA Cleartops are one such tube. I finally found a 12AU7 that is more dynamic with tons of detail and snap... the Siemens E82CC. Probably any Siemens Halske will do. Seriously non-microphonic.

[PatOMalley]

what i meant by "Probably any Siemens Halske will do." is that any year or version of the 12AU7 variant will do. 

[analog97]

I have had the same experience with "tube squeal" that is reported.  I built the Cornet2 first and had microphonics in the 12ax7's.  That was cured by using Sovtek 12ax7 LPS's.  Then I built a Clarinet (because I was SOOOOO happy with the Cornet2).  Again, the same problem.  My current squeal is intermittent and not a HUGE problem, so I am shopping for some recommended, less-prone-to-squeal 12au7's.  The chat here has been VERY helpful, so thanks.  My take (guess) supports JH's, in that highly variable tube quality control is the likely culprit.  The only down-side of tubes IMO is they are simply "quirky".  I have limited experience, though and it does seem odd that someone as experienced as JH does not run into this problem routinely.  Oh, well......I seem to have a close, personal relationship with Mr. Murphy.....

[hagtech]

it does seem odd that someone as experienced as JH does not run into this problem routinely

Perhaps because I am an equipment manufacturer the tube companies sell me a higher grade?  I never actually considered that before.  Maybe I get batches with better quality control?  I dunno.  It looks like a random box to me.

There is also the possibility that the problem doesn't show up with a 24 hour burn-in.  Then again, I can't think of any complaints from customers who have bought pre-assembled and tested units.  I've never had to send out a replacement tube.

Or maybe, maybe it is because of my VacuTrace tube screening process?  I end up rejecting all tubes that don't exhibit a reasonable match or reasonable looking curves.  THAT makes sense.  Considering I chuck about 30% of all incoming tubes, it appears I have solved a problem without even knowing it.

jh

[analog97]

JH's answers were enlightening!!!  Your screening/testing/pitching tubes sounds most likely.  I would like to buy a couple of your "stock", i.e. tested 12au7's for my Carinet.  I have an order pending with your company.  Is it possible to ship in my order?  Sorry for being a pain...don't hesitate to say no and I will look elsewhere.

[mclaren]

Thanks for your replies. Building a Clarinet is the first electronic project I've done and this "squeal" problem has been a little disappointing (great to see the very helpful comments on this forum though). I guess I expected that if I built my clarinet correctly it would run without any problems. As others have experienced this "tube squeal" issue maybe the Hagerman kit manuals should mention something about it, along with some tube recommendations. The EI 12AU7s I purchased clearly are not a good choice and should be removed from the Clarinet parts list.

Along with analog97 I would be happy to buy a pair of JH tested 12AU7s. Name your price Jim!

Mike

[analog97]

Simple math involved here.  If JH throws out 30% of his tubes, then each tube has a 0.7 Pr of being "good".    That means for us who order 2 tubes, the probability that both will be "good" is .7 x .7= .49.     Yeah, without a Vacutrace we customers have only a 50-50 chance of getting 2 "good" tubes.     CRAP!!!!!

[GRD]

Yeah - I've had some spotty luck with new production tubes I purchased retail from guitar shops.  One option is to buy from someone who tests before selling.  One vendor with a good reputation is Jim McShane (check out audioasylum).  I'm sure there are others.

http://pages.prodigy.net/jimmcshane/tubes.htm

[robertwstephens]

I second the Jim McShane referral for tubes.  Jim gives first rate personalized service!  Peace.  Robert

[mclaren]

Thanks to everyone for their advice. I will try some NOS tubes, starting with some RFT ECC82's as suggested by Eric H. They are reasonably priced and readily available.