Tubes

[fatcat]

My silverface Dual Showman head started acting up so I changed a tube or two(only 2 on hand)and I'll be damed if one Svetlana 12AX7 wasn't michrophonic right out of the box.
PHRRRR...

[goofyfoot]

Bummer, man. I know it's just a vacuum tube but it IS one of the disappointment moments, for sure. Peace, out.....Goofyfoot.

[soundmasterg]

The quality of today's tubes aren't as good as the NOS stuff, but that would still happen sometimes with new tubes back in the 50's and 60's too. Its hard to make a 12AX7 which has high gain and not get microphonics. That said, the Svetlana 12AX7's don't have a good reputation if you're talking about the Svetlana factory in St. Petersburg. They have to sell their tubes in the US and Canada under the Winged C name since around 2002. If you're talking about the ones that are currently sold as Svetlana, those are made in the Saratov factory that makes Sovtek, EH, Mullard reissue, Tung-Sol reissue, etc.

BTW, don't throw that tube out. It can be used where microphonics don't matter as much like in a phase inverter spot or a trem oscillator for example and it will work just fine.

Greg

[fatcat]

Yep, that's where it ended up, as the phase inverter,which was the worst of the bad ones.


The box just states Made in Russia.
I ordered 2 Sovteks to try next.
Too bad that I'm out of the old stock tubes that I had from "the day".

[soundmasterg]

They were probably the Saratov ones, which are the same as Sovteks. Try and get some JJ's from Eurotubes, or look around for some of the Tung-Sol reissues from the tubestore or other places that sell them. I've had great luck with the new Tung-Sols myself.

Greg

[fatcat]

The 2 Sovtek 12AX7 EH tubes arrived Wednesday and got planted while the turkey was cooking.All of the preamp tubes are new now.
The amp sounds better and isn't complaining now.
Today I took out and visually compared the two different makes, and they look the same inside, the EHs are Electro Harmonix, but look the same except for a bit more silvering from the getter flashoff.
Done tinkering for now.

[goofyfoot]

They were probably the Saratov ones, which are the same as Sovteks. Try and get some JJ's from Eurotubes, or look around for some of the Tung-Sol reissues from the tubestore or other places that sell them. I've had great luck with the new Tung-Sols myself.

Greg

JJ's have been quite kind to my tube amps of late (last several years). I'm happy with their tone and reliability in both the power and preamp sections. They seem to deliver a cool edge to the overall sound of each amp. But like anything else, it's great if you can spare the change and experiment with different tube makes and models. Just my dos centavos' worth. Regards.....Goofyfoot.

[soundmasterg]

Yes, the EH, Tung-Sol reissue, Svetlana, Mullard, and Sovtek are all made in the Saratov, Russia factory that is owned and operated by New Sensor and Mike Matthews. The EH is the same tube as the the Svetlana ones. The Sovtek 12AX7LP/LPS and Tung-Sol reissue 12AX7 are different and superior to the others made in the factory. The Tung-Sols especially work well in vintage style amps. JJ's are also good though I've heard reports recently of some quality control issues. Glad you found something that will work for you.

Greg

[fatcat]

As it turns out, it wasn't a tube problem after all, but it had to get a lot worse for me to crack into it and solve the problem.
It was a cold solder joint on the bottom of the tag board, and it took some time to find and fix.
Reassembling the head gives a couple of tight-spots to have to work with, to get the nuts on the chassis hanger screws.