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NOS Tube Score (Expert Assistance Needed!)!

ajbergren

Member
Messages
187
[FONT=Verdana, Arial]Today, I was lucky to obtain (free of charge, although I offered to pay!) several NOS tubes.

2 x GE 12AX7A: Labeled Marconi Radiotron, with a vertical PB. Also labeled 12AX7A/7025/Made in Canada

2 x GE 5751: 5751/USA, Five stars also has MT/RT 188-5 on the tube and 165-0548 on the box.

2 x Sylvania 12AT7: Made in Poland

1 x Sylvania 12AT7: Made in USA, ge ACZ labels, also has 12AY7/ECC81/USA in small gray letters.

1 x Sylvania 12AX7A: One made in USA, has red letters that read Be?????, the other is labeled 7025A/12AX7A/Canada, and says Sylvania with the electron bolt symbol and Made in Canada, big vertical PT, and small horizontal DJC

1 x National 12AX7A: Made in USSR, labeled Sovtek

1 x RCA 5Y3: RCA, made in USA, not other significant markings



Okay, here are my questions:

Are these any good? I know the GE 5751's are awesome, but what are the Marconi 12AX7's (GE labels)?

Also, how about those Polish 12AT7s?

Basically, I have two main amplifiers that I would consider using these in:
a 1965 Princeton Reverb
a Victoria Tweed Deluxe Clone

I also have a 1979 Champ and an Orange Tiny Terror.

Would any of those 12AT7s be useful for the reverb driver in the PR? I think the USA sylvania might be useful, but I do know the JAN Philips are not good for this position, as they do not handle the heat (they go bad quickly).

How about the 12AX7's? are the Marconi's any good? How about the Sylvania's?

Any help identifying the origins of these tubes (i.e., original manufacturers', or other info) would be awesome!










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teleamp

Senior Member
Messages
3,478
Great score!!! Those should last you a lifetime in your amps. They should all be better than any current offerings, use them all. Yes, the 12AT7's will be great for the PR reverb and PI posistions, don't be drawn into the internet hype about which ones won't last, there are way too many variables that could have occured for those conclusions to be made. Let your ears be the judge.

MikeY
 

teleman1

Silver Supporting Member
Messages
15,096
They are all great tubes and probably test new. TRy the 12ax7's & 5751's in your amps,(they are basically the same tube. The 5y3 would work great in the champ,but it would be nice to test that one for sure. I fried a Champ circuit witha bad 5y3,it toasted the tranny. THe 12at7 should be great in the PR.
 

Blue Strat

Member
Messages
30,202
It's the JAN GE 12AT7s that don't tend to work well or last as reverb drivers, not the Philips or Sylvanias.

Regarding the rest of them, use your ears....that's the only thing that matters.
 

slider313

Gold Supporting Member
Messages
8,256
I bought a lot of 50 GE 6201/12AT7's a couple of years ago for a very good price. I tested evey one in my Eico 667 and in the reverb send position of my original '65 Deluxe Reverb. While they all tested good in the Eico, 22 produced noise in the Deluxe's reverb send. The quiet ones work quite well in that position and I have had one in there for over a year with no problems. The problem would be buying these from a source that doesn't test for noise and microphonics. The ones that are microphonic can be used without a problem in the driver/phase inverter spot.
 

AdmiralB

Member
Messages
3,062
It's the JAN GE 12AT7s that don't tend to work well or last as reverb drivers, not the Philips or Sylvanias.
That's only in the mid-'70s SF Fenders that run the reverb driver too hot. If you change the cathode resistor back to BF value, any decent 12AT7 will be fine.
 

slider313

Gold Supporting Member
Messages
8,256
With any small signal tube, the best thing to do is put it in the amp and listen. The tubes made in Poland may sound good. The Princeton Reverb's reverb send, V2 , will weed out any tube producing noise.
 

ajbergren

Member
Messages
187
Cool, thanks all!!

The tubes sound great! I put a 5751 in V1 in the Deluxe and a GE 12AX7 in V2. Then I put an RCA 7025 in V1 in the PR, followed by the USA Sylvania 12AT7 in V2 (Reverb Send- V3 is Reverb recovery), a Canadian 12AX7 in V3, and the USA Sylvania 12AX7 in V4. The amps sound great!!

Thanks again!
 

Blue Strat

Member
Messages
30,202
That's only in the mid-'70s SF Fenders that run the reverb driver too hot. If you change the cathode resistor back to BF value, any decent 12AT7 will be fine.
I'm pretty sure they have problems in BF and BF'd reverb driver circuits as well, though I haven't kept a detailed data base. But then again, I've only sold about 80,000 tubes and worked on 100s of amps so what do I know? ;)
 

ajbergren

Member
Messages
187
Well, no, but they could be generally recognized as "poor quality." I had a bad experience with a IC brand tube (I think it was Japan or something, but may have been East Europe), and rather than struggle with using crappy tubes, I'd rather order good ones from you, Mike! Also, my major concern was burning out the 12AT7s in the reverb driver, when they would have been good elsewhere, which would have been a pity.

I do think the Poles probably made pretty good tubes, but I'm not up on these things!! I think it is pretty cool that I found 3 tubes that were made in Canada (I did not realize there were that many around).

Thanks again!
 

AdmiralB

Member
Messages
3,062
I'm pretty sure they have problems in BF and BF'd reverb driver circuits as well, though I haven't kept a detailed data base.
That would have been news to Fender, I suppose, since GE was the stock OEM tube for them for quite a while in the SF era, immediately pre-Sylvania.

It's the amps with the 470-ohm cathode resistor on the 12AT7 that have problems with non-Sylvanias. These are mostly the SF amps with the pull-master, but not UL. They also have REALLY high voltage (440V or more) on the plates there. Going back to the 2.2K resistor makes the amp happy with 'regular' 12AT7s again and doesn't affect the tone. They d

But then again, I've only sold about 80,000 tubes and worked on 100s of amps so what do I know? ;)
Yeah. I propose that Aspen Pittman has sold a lot more tubes than that, and been inside more amps too. It doesn't mean I'm going to believe everything he says.
 

VacuumVoodoo

Member
Messages
1,547
Sylvania 12AT7 "Made in Poland" - this one is a rare bird. It's an RFT made actually in GDR. Most probably Sylwania placed an order with Telam or Polam who were unable to deliver on time and bought bulk from RFT, stamped and re-exported. Poles paid the Germans in ham and butter, Sylvania paid Poles in USD so Poles could buy Decca radars for ships they were building for Soviet Navy which soviets paid Poles in reprints of Lenins works which the Poles in turn immediately sold to paper recycling facilities and printed books for US publishing houses and got their USD back. Those were the days....
 




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