Tube- 6F6

Seems to be a power tube indeed.

http://www.tubesandmore.com/

Hi Witchdoctor,

Here's some hard data for the 6F6. It's listed as a metal-jacket type pentode power tube. I've found the metal-jacket tubes aren't optimal, and tend to have microphonic and heat dissipation problems in guitar amplifier service, although that applies mostly when used as preamp tubes. A metal-jacketed power tube would be less sensitive to the more common microphonic characteristics of metal-jacketed tubes, and the heat problem would depend greatly on how the tube is operated (Class A, AB1, etc) and the voltages and currents applied. YMMV (Your Mileage May Vary) Hope that helps.

6F6 data --> http://www.nj7p.org/Tube4.php?tube=6F6

This one is a big bottle style. I got an email from THD, who makes the Univlve, the amp I want to try it in, and they said go for it... it sounds pretty sweet, a bit less drivey and very clear and articulate. Score!

It's an old power pentode that was popular in radios. The 6V6 is usually a good substitute, and in a lot of applications a 6Y6 or 6W6 would work well. For substituting any of those for 6V6s in guitar amps, you need to look at the operating conditions. Typically guitar amps run the output tubes way over the rated voltages for 6V6s, and these older tubes don't take that overrating well.

For that matter, 6L6s often work well in amps designed for 6V6s (one of the tube companies, I think ElectroHarmonix, was selling the cheap sort of Russian 6L6s as "6V6EH" or some such a few years back), and you've got no worries about overstressing them in a 6V6 application. It's possible to overload the heater secondary of your power transformer by using tubes with a higher heater current, but unlikely to hurt anything in practice.

I'm using it in a THD Univalve, which accepts tons of different power tubes so you can experiment with tones. Almost any power tube, tons of different preamp tubes. It also has a switch that allows you to lower the plate voltage for 6V6 tubes and a few others. It's very versatile, I have a small tube library these days, and it is fun to change them out.

That sounds like a nice setup! In that case, do get a 6Y6GT and a 6W6GT. They're common old tubes. Someone, maybe Antique Electronic Supply, was selling off a bunch of the old "Coke Bottle" 6Y6Gs cheap a while back, suggesting them as subs for 6V6 in nondemanding applications. It was another radio power tube. The 6W6GT was a common vertical output amplifier in black-and-white TV sets. I'm pretty sure the basing is the same for all of them, but I haven't checked just now, so check before you order.