Power Tubes... Can they cause volume (power) loss as they age?

[Ch0jin]

Thanks guys, that's pretty much what I was thinking too. I'll sort a new set of toobs and see how I go from there. To answer a few questions...

Are they real 6L6's? I'd always assumed so yeah. At least they are stamped "Sovtek 6L6WXT" and "Made in Russia" Here's a pic..


Clash of the Cold War Rivals I by Ch0jiN, on Flickr

I have the schematic, I repaired some dry jointed filter caps not long ago to fix an intermittent hum problem. I removed and physically inspected the main filter caps and they "looked" fine. I have to recap and older (1970's) Peavey Bass head soon too so maybe I'll tackle both of them.

Nothing sounds particularly "weird" at apartment volume I hadn't noticed anything, it's just when I get it up to 10

Regarding speakers, I totally agree with you Deeaa, however I have tried it with my 4x12 as well and it still sounded wimpy (although I did have the impedance mismatched as I mentioned before)

That said, I have no data on the speakers in my 4x12 other than they were made in the 60's (cause that's when the cab was made) and that they were made locally. They might be horribly inefficient....or not I guess I'll have to A/B the cab with something else at some point.

Here's a pic if your curious..


Fluxing Hi by Ch0jiN, on Flickr

Oh and Tig.... Didn't mean to offend you with my Solid State reference. If it makes you feel better, it wasn't my amp Both my guitar amps have Toobs.

[tunghaichuan***]

Thanks guys, that's pretty much what I was thinking too. I'll sort a new set of toobs and see how I go from there. To answer a few questions...

Are they real 6L6's? I'd always assumed so yeah. At least they are stamped "Sovtek 6L6WXT" and "Made in Russia" Here's a pic..


Clash of the Cold War Rivals I by Ch0jiN, on Flickr

Just as I suspected. Those are 6П3С-EB (In Cyrillic, 6P3S-EV in Latin) tubes. They are rebased Sovtek "5881" tubes. The first 6П3С-EB tubes exported from Russia back in the early 90s had a coin base and were labled "5881." They were nothing like a real Tung-sol 5881. Nor were they like a 6L6GC. Rather they were just similar enough to use in 6L6 circuits. At the time, they were a godsend because GE had shut down their factory in Kentucky and it was the first time a 6L6 type tube wasn't in production since the 1930s. Sovtek then began to have the same tube manufactured with a full-size base (identical to yours) so that the claws in Fender amps could grip them. The coin based tubes didn't fit in Fender amps right. Sovtek relabeled the tube 6L6WXT. The WXT suffix is a tip-off: no real Western-made tube had this suffix, and it is meaningless under the Western tube designation scheme.

The tube is very rugged and long lasting (as the EB/EV suffix denotes). It however does not produce as much power in a 6L6 circuit as a real 6L6. Also, IIRC, you have to bias them really hot to get them to sound good. They require a different impedance to develop full power. The Sovtek amps that use these as the stock tube have both the right OT and very high B+ levels to get them to develop full power.

I ran an experiment with two of my samples (I have a matched quad of the identical tube.) I have a Champ-style circuit that has beefed up transformers so that I can run bigger power tubes. I've run a 6550, EL34 and 6L6s in it. I tried two of my Sovtek 6L6WXT tubes in it and biased the amp to 40W dissipation in Class A. One tube had a hint of red-plating, the other the other none at all. So it's not really a mini 6550, but the 6П3С-EB will take a lot of abuse that would kill a real 6L6GC very fast.

Luckily, there are some real 6L6GC spec tubes being produced today. However, none are particularly robust, or long lasting as NOS/Western. I would bet that your amp was designed for the Western 6L6GC style tube, knowing Peavey.

[Tig***]

Just as I suspected. Those are 6П3С-EB (In Cyrillic, 6P3S-EV in Latin) tubes. They are rebased Sovtek "5881" tubes. The first 6П3С-EB tubes exported from Russia back in the early 90s had a coin base and were labled "5881." They were nothing like a real Tung-sol 5881. Nor were they like a 6L6GC. Rather they were just similar enough to use in 6L6 circuits. At the time, they were a godsend because GE had shut down their factory in Kentucky and it was the first time a 6L6 type tube wasn't in production since the 1930s. Sovtek then began to have the same tube manufactured with a full-size base (identical to yours) so that the claws in Fender amps could grip them. The coin based tubes didn't fit in Fender amps right. Sovtek relabeled the tube 6L6WXT. The WXT suffix is a tip-off: no real Western-made tube had this suffix, and it is meaningless under the Western tube designation scheme...

Wow!