What causes a tube to "sing"?

[Shadowfax]

I use my main setup as the front L&R for HT. When I do that, I need to set my volume knobs to about 1 o'clock to match the volume from my Integra.

It's then for the most part that I realize that 1 or more of the 4 tubes in my VAC pre are singing, or squealing with a high pitch sound that will call all the dogs home.

What causes this and how can I correct it? Or do I have bad tubes?

[mep]

Sounds like you have some microphonic tubes. Try using tube dampening rings and buying tubes that are tested for microphonics.

[Shadowfax]

Sounds like you have some microphonic tubes. Try using tube dampening rings and buying tubes that are tested for microphonics.

Thanks mep. I actually bought these a few years ago right from VAC but have been wondering what I can do better or different.

[bzr]

Brian, at least you have a great selection out there to choose from

[octadyndude]

Found this on Vac's website
http://www.vac-amps.com/manuals/Manual_CPA1_Mk3.pdf

[Shadowfax]

Thanks George. Sounds like I need to look for some new tubes.

Kev, the selection is actually the problem if one doesn't really want to buy several sets to find out. I've had JJs, Sovtek, and whatever these no name Chinese tubes are from VAC, which were better than the others.

[octadyndude]

Brian It's very hard to pick tubes based on peoples impressions who have them. Unless they have the same system as you there are many variables. An example is when I had Dyn C1 speakers. The original Tung Sol 6550 black plate was killer and the KT120 was the worst. When I upgraded to Raidho D1's the TS 6550 sounded pretty bad and the KT120 was better. Mullards were great with the Dyn's and pretty bad with the Ho's. Of course there is YOUR personal taste which could be the opposite of mine. Some manufacturers design their amp based on a certain tube. The original Octaves were designed around the manufacturer SED. That was later changed just before the SED plant was closed which made tube rolling more reliable. I would e-mail VAC and ask for their recommendation. Could be their pre was designed around the 'no name Chinese tube' which is possibly why they sounded better.

Good luck :thumbsup:

[Shadowfax]

Thanks again George. I actually spoke to Kevin for about 30 minutes at that time and he basically suggested I buy what they were putting in current production Pre amps. I went with his rec and was pleased with the sound overall, but also put some NOS RCA Clear Tops 6CG7/6FQ7 in my Counterpoint for another nice improvement.

Guess I need to roll the dice if I can't find someone to borrow a few from to try out.

[MikeCh]

Hi Brian,

Does the squealing sound come thru the speakers at this increased volume?....or from the tubes themselves while in-chassis? (I can't tell from your OP).

Assuming re-tubing the linestage is the fix, how much money do you want to spend on tubes?

[Shadowfax]

I am pretty sure it is bleeding thru the speakers, but I need to narrow down which one/s are doing it.

Wouldn't mind keeping the 4 tubes at $100 or so.

[MikeCh]

It might be worth it just to get a whole new set of four tubes (reissues instead of NOS if you want to keep all four to around $100) and see if the problem gets resolved. If it doesn't fix the issue, then you're not out too much coin and you at least have a new set of tubes for future use.

If it does fix the ringing, you can then swap in individual tubes from the old set of four to determine which one(s) are causing the noise.

For new-reissue tubes, somewhere like the Tube Store or Tube Depot will likely have the best prices. I'd suggest other sources that deal with NOS but many of them will be $100 or more each....

[MikeCh]

Brian,

What did you end up deciding to do for tubes?

[Shadowfax]

Brian,

What did you end up deciding to do for tubes?

The ringing sort of went away so I was unable to determine which tube it was, or even if it was the Pre and not the Amp tubes.
Last night I played around rolling the few tubes I did have on hand. The current AX7s were right from VAC and are no-name Made in China tubes. I tried a set of Sovtek LPS's and a set of WXT+'s for that spot. I also had a pair of JJ AU7s that were replaced by VAC- Jan Phillips tubes. The JJs sucked big time and went back to the Jan-Phillips in 10 minutes.

As per the Sovteks, the LPS gave me more highs and tighter bass but lost the real nice midrange. The Jan tubes ar a bit mushy on the bottom end, but sound more like tubes. The Sovtek WXT+ tubes were even more bright and harsh with more of a SS sound. For the moment I left the LPS's in for a few days but will most likely go back to the China tubes while I decide if I really need new ones or not. I may just concentrate on the 12AX7s because I like to use the passive buffered mode and it only uses the AX7s.

Thanks!

[William]

The ringing sort of went away so I was unable to determine which tube it was, or even if it was the Pre and not the Amp tubes.
Last night I played around rolling the few tubes I did have on hand. The current AX7s were right from VAC and are no-name Made in China tubes. I tried a set of Sovtek LPS's and a set of WXT+'s for that spot. I also had a pair of JJ AU7s that were replaced by VAC- Jan Phillips tubes. The JJs sucked big time and went back to the Jan-Phillips in 10 minutes.

As per the Sovteks, the LPS gave me more highs and tighter bass but lost the real nice midrange. The Jan tubes ar a bit mushy on the bottom end, but sound more like tubes. The Sovtek WXT+ tubes were even more bright and harsh with more of a SS sound. For the moment I left the LPS's in for a few days but will most likely go back to the China tubes while I decide if I really need new ones or not. I may just concentrate on the 12AX7s because I like to use the passive buffered mode and it only uses the AX7s.

Thanks!
I would recommend NOS Sylvania 5751 3 mica black plates. you wont have to worry about micro phonics and the tubes sound glorious.

[MikeCh]

I would recommend NOS Sylvania 5751 3 mica black plates. you wont have to worry about micro phonics and the tubes sound glorious.

Agreed. 1950's Sylvania 5751 triple mica black plate are what I run in my linestage as well and they are beauties. But, Brian already said he was in for $100 total on all four tubes (in order to sort out the bad one/ones if there were any).

Considering the Sylvania NOS 5751's run around $100 ea if you can find a reliable source, I'd think they are beyond his budget.....but maybe not?

[Shadowfax]

I think because of the buffered passive mode being most important, and the AU7s are more or less adding gain in normal mode, I am concentrating on the AX7s. I stopped in at Quest for Sound yesterday to drop of a Rotel Receiver for repair, I chatted with the owner, Steve Monte (he hand builds Sound Quest Amps and CD Players) and after describing what I was looking for and what I thought about the Sovteks, he recommended Genalex Gold Lions he had for $35 each which is not bad from internet prices.

There is another guy over at AK that is supposed to email me a short list of what he has in stock of NOS tubes. I'm not in a big hurry and just want to make a good choice and be happy for a while. Thanks for all the help.

[Shadowfax]

I would recommend NOS Sylvania 5751 3 mica black plates. you wont have to worry about micro phonics and the tubes sound glorious.

Yeah, my budget is just not there at the moment. From what I read, they do seem like a great tube. You can send me your worn out ones if they are taking up space :)

[Shadowfax]

I think I was able to figure out which tube was making noise and it happens to be one of the Jan-Phillips 12AU7s I got from Kevin Hayes at VAC. The last time it started singing, I gave it a tiny flick with my fingernail and it popped and stopped making noise and has yet to do it again.

I was actually hoping it was one of the no name China AX7s because that is what I would like to upgrade. The Genalex Golden Lion Gold Pins were recommended by my dealer/repair guy after describing what I was looking for.

[jdandy]

Brian.......Having read this entire thread I think it would be money well spent to replace both the Chinese 12AX7's and the JAN-Philips 12AU7 tubes. Your VAC CLA1 MkII is unique with its active and passive modes. Without a schematic I am only guessing but in active mode I assume the 12AU7 tubes are acting as gain stage amplifiers while the 12AX7 tubes are acting as impedance matching buffers for the preamp outputs. In the passive mode it appears the 12AU7 gain stage tubes are bypassed and the audio signal is then controlled by the passive volume control while the output impedance is set by the 12AX7 buffer tubes. In both applications the tubes play a critical roll in the signal path.

My experience with JAN-Philips tubes has been limited to their 12AT7 tubes in some MC275 amps but I found them to be a bit soft in the lowest frequencies and had a tendency to be microphonic. This leads me to believe this mid-quality tube issue is what you are experiencing with your JAN-Philips 12AU7 tubes. I would suggest you try Genalex Gold Lion B749 / ECC82 / 12AU7 tubes. According to New Sensor these tubes have been designed specifically for audio use with noise canceling spiral filaments, thick mica spacers, and gold plated pins. And while you're at it replace the 12AX7 buffer tubes with Gold Lion ECC83/B759/12AX7 tubes. My experience with Gold Lion 12AX7 tubes has demonstrated beneficial performance gains over many other tubes I have rolled into C1000T and C2300 preamps and three MC275 MkV power amps. I have made direct comparisons of the Gold Lion tubes with NOS Mullard, Tung-Sol gold pin, Telefunken, and cheap Chinese tubes (unknown brand). The Gold Lion ECC83/B759/12AX7 tubes were the closest to performing like the excellent and expensive Telefunken ECC83 / 12AX7 tubes. The Gold Lion's are reasonably priced, both the 12AU7 and the 12AX7, usually less than $40.00 each in matched pairs or quads.

I don't think you are getting the last percentage of premium performance from your VAC preamp with the tubes you are currently using. Tube rolling can get expensive as you search and purchase different tubes looking for the holy grail. My experience over several years of doing just that has led me to believe the Russian made Gold Lion tubes represent some of the best sounding current production tubes available at a price that won't require a second mortgage.

[Shadowfax]

Thanks for that confirmation Dan. I am thinking the same thing about replacing them all.

I am pretty sure you have the workings of my VAC correct and I do listen to the Buffered Passive mode when I don't want the extra gain during late nights when wifey is sleeping. I plan on keeping the VAC for a few more years until I am forced to downsize my home and systems so it would be money well spent.

[Shadowfax]

I just ordered 2 matched pairs of Genalex Gold Lion Gold Pin versions of 12AX7s and 12AU7s

Looking forward to hearing how much better my Pre can sound with better tubes in it.

Thanks for the help and suggestion!

[jdandy]

I just ordered 2 matched pairs of Genalex Gold Lion Gold Pin versions of 12AX7s and 12AU7s

Looking forward to hearing how much better my Pre can sound with better tubes in it.

Thanks for the help and suggestion!

Brian.......Good move. I think you will be pleasantly surprised at the improved performance of your VAC preamplifier. That is too nice a component to be using marginal tubes in it. Looking forward to your impressions. Remember, it will take the 12AX7 and 12AU7 tubes approximately 40 to 50 hours to develope their permanent voice. Until they are fully broken in keep the VAC in the mode that operates all the tubes at once.

[Shadowfax]

Thanks Dan! I will keep in in normal gain for the breakin and will report back after that.