Plate voltage of NOS RCA and NOS Tung Sol??

[Jared Purdy]

Greetings!

Wow, it's been ages since I've been here, but it's good to be posting again. I'm in the market for some nice 6V6 tubes, and I'm thinking about picking up either a pair of NOS RCA or NOS 1960's Tung Sol. I have a Swart AST Master 112 combo, and I was told by Michael Swart that the tubes have to be able to handle 405 volts. I have been using Tung Sol 6V6 re-issues but the amp fries them after a couple of months as they are only rated for around 300-350 volts. JJ 6V6 work fine, but I don't like the tone from them.

So if I am going to spend some money on some nice tubes, I want to be sure that they won't cooked in two months. Can anyone tell me if either of those tubes can handle 405 volts?

Regards, Jared Purdy

[Justin Thomas]

My 79 Champ came with an RCA 6V6GTA when I bought it, about 6 years ago. Runs ~425 on plates, forget what I have the screen at. Never had a problem with it in the years I had it til I decided to retire it when I got some more Used Old Stock tubes. I still have the RCA. Right now it's got a Sylvania, been in for about a year, no issues. I tried EH - smoked a pair within a month (shorted). And someone else here suggested that it's not necessarily the voltage that kills (NOS) tubes, it's overdissipation and/or current. Buy a nice old tube and don't bias it too hot and you'll likely be okay. Just make sure it's a 6V6GTA - the newest version of the old tube. We've got a GT lying around that I'm tempted to try, but it's not mine... but as always, no guarantees... And, neither of those NOS tubes are spec'd to handle over 360V! Fender just liked to abuse them, I guess. But they've served well for a while now, huh?

HTH,
Justin

[Jared Purdy]

Justin, thank you very much. Maybe I'll try those RCA 6V6

[Jazz P Bass]

Try to keep in mind what Justin said about the current being more of an issue than the voltage.
If you are simply throwing tubes in the amp & not monitoring the current draw, you are not going to 'get' anywhere.

[Jared Purdy]

Thanks. How do I monitor the current draw? Swart amps don't have a built in bias adjustment.

[pdf64]

With the amp isolated and caps discharged, measure the resistance cathode resistor.
When in operational mode, static conditions, measure the Vdc across the cathode resistor.
Plate + screen current for both tubes combined = V/R from the measurements above.
Pete

[Jazz P Bass]

Judging from the Swart web page, these amps are running a very hot Class A/B.
Meaning the tubes will draw a significant current at idle.
Have you talked to Michael at Swart what to expect (tube change/ tone wise)?
As particular as he seems to be about his amps, he may have the tubes that you want.

[Steve Conner]

Given the price of NOS tubes, it might be worth getting them from Swart with a warranty.