GT-6L6-GE power tube?

Anode dissipation values.
6L6GT plate dissipation 11W (source The Valve Museum)
6L6GC plate dissipation 30W (source Svetlana Electronic Devices)
GT-6L6-GE plate dissipation 20 - 25W (source Stew Mac) Made in China!
So, derate as required using the 6L6 data.

 

Why not set it up using a formula. Here's how to do it;
Some like them hot some cold. Without getting too heavy with maths and algebra, a tech from a market leader amp maker (no names mentioned) who tends to bias on the hot side, told me this.

The maximum output from an 6L6-GE is about 20 watts. So measure the anode voltage of the amp, for this exercise we will assume that to be 445 volts. Divide the 20 by the 445 then multiply by 0.7 the answer in ma. is the 70% plate load bias setting required for that amplifier.

The 0.7 means 70% Hot anode / plate dissipation. Therefore you can use 0.5 (50%) as a Cool AB setting, 0.6 (60%) as a Warmer AB setting the one I would prefer. Or go for the 0.7 or even 0.75 (70 - 75%) if you like it hot.

Example: 20 / 445 X 0.7 = 31.4 ma. Bias

The bias figure will depend on the anode voltage which will vary according to the current drawn by the valve. More current less volts, less current more volts. So you may need to do the calculation several times if large adjustments are made.

Example 2. 20 / 480 X 0.7 = 29.1 ma. Bias

Example 3. 20 / 410 X 0.7 = 34.1 ma. Bias


Here is an EL34 example set as Class A with 300 volts on the plate / anode.

25 watts max o/p of the valve divide by plate volts 300 multiply by 1 = bias current requirement for class A operation. Example. 25 / 300 X 1 = 0.083 = 83ma. or 25 / 350 X 1 = 0.071 = 71ma.

Not rocket science - dead easy elementary stuff.

 

They are just GT's reissue version of the old General Electric 6L6GC. I'd just bias them as that. Stew Mac likely doesn't know any more what they are than anyone else. Reportedly "medium output" though. But who knows what all the various 6L6GC vintage tubes actually were?

"The Groove Tubes GT-6L6-GE is a faithful reproduction of the original "clear top" 6L6. The flagship of the GT 6L6 line, it looks and sounds exactly like the original G.E. tube used by Fender in the '50s and '60s. It took more than four years to develop, and has stunning clarity and power. Our most recommended 6L6."

 

That's where I would start, see how it sounds.

 

You know it when you see it ... the color of the hot elements in a toaster.

 

Nah, it won't be that far off.

 

So, see the dark grey bits? When they are dull red, it's a bad thing. When I change tubes, I turn the lights off (amps like romantic atmosphere) and play loudly while looking into the back of the amp ... for several minutes. Usually if there's a problem, you'll see it. Usually.

 

If memory serves, I recall reading sometime in the early-mid 90s about GT (Aspen Pittman, right?) coming into possession of one of GEs last tube manufacturing machines and some of their plate material (it's really a coating, innit?) and applying some reverse engineering to having those late-model GE 6L6GCs "recreated" at a facility abroad (don't recall where).

Sad thing is, as a bit of a pack-rat and real nut about saving my magazines over the years, I probably still have that issue down in the man cave somewhere.

 

Was that the IEEE Spectrum article?

 

It’s pretty unmistakable when the plates start to turn red like red hot metal. Look at them working in a dark room.

 

Those are purported to be GE 6L6GC replicas and are very close. Nearly 20 years ago GT founder Aspen Pittman secured some original GE tooling for their old 6L6GC, which was OEM in most Fender combo amps through the blackface/silverface golden era of the 60s. (BTW, shorter bottle RCA 6L6GCs were OEM in the heads, not the combo amps.) Aspen was attempting USA production but couldn't do it profitably, so the tooling went to China for actual production. If you look at them side by side with a vintage GE 6L6GC they look nearly identical, and to my ears they sound fat & full like the originals. They are 30w tubes so bias as you would a regular 6L6GC.

 

red plating:

 

The only thing bad that I have heard about them is that at least when they were first brought out they seemed to have a bit higher failure rate than than GT would have liked for their premier power tube.

I have two sets and have used one set at around 65-70% plate dissipation (for a 6L6GC) in a Fender Vibro-King for long enough to know that I know they're going to at least survive a decent amount of time at decent volume and they sound great. I've burned the second set in without issues, as well.

Great tubes considering their cost compared to old stock.