What happens to the sound of a 12AU7 tube when...

geowak · « **Reply #40 on:** 24 Mar 2013, 03:42 pm »

I had a pair of NOS RCA clear tops years ago and they sounded very good. Now I am using some NOS Sylvania and GE.
I have used some NOS mil grade that sound very good to me. I bought the Mil grade because they were built to a set standard which turned out to sound very good compared to the new tubes made today. The exception would be the Genelex re-issue Gold Lion KT88's (power tubes). Those were pricey...

TJHUB · « **Reply #41 on:** 25 Mar 2013, 08:57 pm »

The RCA clear tops have been in for about an hour now, and they already sound WAY better than the JJ tubes. I hope they break in nicely.

Freo-1 · « **Reply #42 on:** 25 Mar 2013, 09:11 pm »

No surprise here. RCA made very good tubes overall.

TJHUB · « **Reply #43 on:** 27 Mar 2013, 01:34 am »

I unfortunately got a lesson in microphonic tubes today. Yikes it was really bad! I couldn't even lightly touch any part of my preamp and I could hear it loudly through my speakers. One tube was REALY bad, and another was just bad. The 2nd matched pair seems fine. So now I'm basically down...again.

Freo-1 · « **Reply #44 on:** 27 Mar 2013, 01:37 am »

Not for long. Help is on its way, via USPS.

TJHUB · « **Reply #45 on:** 27 Mar 2013, 01:39 am »

Quote from: Freo-1 on 27 Mar 2013, 01:37 am

Not for long. Help is on its way, via USPS.

And I can't thank you enough!

Freo-1 · « **Reply #46 on:** 27 Mar 2013, 01:42 am »

No worries. Let's hope at least one of the quads works out OK.

TJHUB · « **Reply #47 on:** 6 Apr 2013, 01:35 am »

Question for the tube guys:

I received my replacement RCA clear tops, and they are microphonic too!! My preamp uses an MU-follower design, so I put the non-microphonic RCA tubes in the front positions, and the microphonic RCA tubes in the back positions. All is now quiet. Should I still get the microphonic tubes replaced? Again? Is it bad to have microphonic tubes if they don't seem to hurt the sound?

medium jim · « **Reply #48 on:** 6 Apr 2013, 01:46 am »

Quote from: TJHUB on 6 Apr 2013, 01:35 am

Question for the tube guys:

I received my replacement RCA clear tops, and they are microphonic too!! My preamp uses an MU-follower design, so I put the non-microphonic RCA tubes in the front positions, and the microphonic RCA tubes in the back positions. All is now quiet. Should I still get the microphonic tubes replaced? Again? Is it bad to have microphonic tubes if they don't seem to hurt the sound?

12AU7's usually are nice and quiet, wonder if you have some caps that are out of spec causing too much current hitting the V1 socket. Consider a 5963 in lieu of the 12AU7, which is an industrial equivalent to the 12AU7 and are noted for being very musical and low microphony. Yes, it is okay to have microphonic tubes that are away from the initial gain stage if they are quiet. Have you tried tube dampers on them?

Just for the record, I have had some 9pin tubes in use that have to be around 12k hours in a couple of my guitar amps that still sound great. I have a pair of Siemens E188CC's in the Output Stage of my CDP that have at min 5k on them and still test NOS.

Jim

ted_b · « **Reply #49 on:** 6 Apr 2013, 02:08 am »

Yes, 5963's and 5814's are what I've been recommending, and they might be a bit mcirophonic, but as long as they don't transmit that in anything but a tap you are fine. I agree that maybe your pre is a little hot there.

FullRangeMan · « **Reply #50 on:** 6 Apr 2013, 02:21 am »

I like this video = How to test a tube for microphonics:
http://www.youtube.com/watch?v=13n1VCR6UXw

Freo-1 · « **Reply #51 on:** 6 Apr 2013, 02:21 am »

Quote from: TJHUB on 6 Apr 2013, 01:35 am

Question for the tube guys:

I received my replacement RCA clear tops, and they are microphonic too!! My preamp uses an MU-follower design, so I put the non-microphonic RCA tubes in the front positions, and the microphonic RCA tubes in the back positions. All is now quiet. Should I still get the microphonic tubes replaced? Again? Is it bad to have microphonic tubes if they don't seem to hurt the sound?

All tubes are microphonic to some extent. It's the nature of their operational principle. 6DJ8 tubes are REALLY bad for that.

Have you tried using the Japan tubes in the back, and the RCA in the front. There is no law that says they all have to match, as long as each channel has the same set of tubes.

TJHUB · « **Reply #52 on:** 6 Apr 2013, 02:39 am »

You guys are starting to lose me. Why question how hot the tubes are running? I had one set of tubes die at over 5k hours, and now two pairs of microphonic tubes. The original Sylvania's were never microphonic, and one pair of RCA tubes seems fine.

I hear the microphonics just touching the preamp or tubes. It is crazy sensitive.

That video is from Brent Jessee. I wonder what he'll say when I call on Monday? I would have thought he would have tested these replacement tubes better.

I haven't tried the Japan tubes in the back. I will tomorrow evening. I did try the JJ tubes in the back with the RCA's in the front. Not good.

Freo-1 · « **Reply #53 on:** 6 Apr 2013, 02:57 am »

I think you simply have had a run of bad luck with dodgy tubes. Since you did not mention microphonics with the other tubes you tried, I'm pretty sure the tubes are at issue. Testing tubes does not generally shake the microphonic issue out. You actually have to play it in a circuit to sort that out, and vendors generally do not do it.

If you buy tubes from a guy like Vintage Tube Services, they do that testing. You also pay for that.

FullRangeMan · « **Reply #54 on:** 6 Apr 2013, 03:08 am »

In the last part of this video they inform also charge ($5 per tube) for testing noise.

medium jim · « **Reply #55 on:** 6 Apr 2013, 03:21 am »

Typically, it will be the 1st stage in the gain circuit that will be where a microphonic tube will be exposed. As the OP has already done, move the noisy tube to the back and find the least noisy for the front. Better yet find several that are quiet in the V1 socket and then find the one that pleases your ear for the coveted V1 spot.

Jim

TJHUB · « **Reply #56 on:** 8 Apr 2013, 10:16 pm »

Unfortunately, I'm back.

Brent Jessee sounds ready to give up on this and offered my money back for yet another pair of microphonic RCA clear tops. I had a long conversation with Brent about tubes, and he felt very strongly that 5814 tubes are no good, and the 5963 tubes might be too dark for me (maybe it was just the tubes he has). And this brings up my next issue. Brent doesn't have anything else for me. So now I have my money back, but no tubes. I did find a vendor that has the exact tubes I used to like, and a slightly older D getter version. However, this has me wondering if I should take this opportunity to find more vendors that might help me before buying the Sylvania's? Any suggestions?

Freo-1 · « **Reply #57 on:** 8 Apr 2013, 10:19 pm »

Quote from: TJHUB on 8 Apr 2013, 10:16 pm

Unfortunately, I'm back.

Brent Jessee sounds ready to give up on this and offered my money back for yet another pair of microphonic RCA clear tops. I had a long conversation with Brent about tubes, and he felt very strongly that 5814 tubes are no good, and the 5963 tubes might be too dark for me (maybe it was just the tubes he has). And this brings up my next issue. Brent doesn't have anything else for me. So now I have my money back, but no tubes. I did find a vendor that has the exact tubes I used to like, and a slightly older D getter version. However, this has me wondering if I should take this opportunity to find more vendors that might help me before buying the Sylvania's? Any suggestions?

Try Radio Electric Supply in FL. They have good prices, and they have a audio guy on hand to discuss. You can also try Vintage Tube Services. The guy there is good, but you will pay for that service.

medium jim · « **Reply #58 on:** 8 Apr 2013, 11:06 pm »

Quote from: Freo-1 on 8 Apr 2013, 10:19 pm

Try Radio Electric Supply in FL. They have good prices, and they have a audio guy on hand to discuss. You can also try Vintage Tube Services. The guy there is good, but you will pay for that service.

I have a bunch of lightly used 1950's and 1960's 12AU7's that I will go through...some are Sylvania's, the others GE's and RCA's. I can test them tomorrow if you would like.

Jim

borism · « **Reply #59 on:** 9 Apr 2013, 01:00 am »

I would also consider talking to Kevin Deal from Upscale Audio. They test all tubes extensively including for microphonics and grade them accordingly. I have had great experience with Upscale.