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Calling MR. Tubelab! 6W6GT?

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According to the datasheet right off TDSL, it's got a maximum anode voltage of 300 and screen grid voltage of 150. kind of unexciting. Max plate dissipation of ~10W, 1.5W for the grid. However, they do list it as being run in triode connection at 225V, so YMMV.

If you're looking at sweep pentodes for TV, you might want to take a gander at the 6DQ5. 990 max anode volts, 190 max for the screen, 24W max anode dissipation. Or, the 6CD6GA is also interesting, at 700 max volts on the plate, 175 for screen, and 20W max plate dissipation.

I can't imagine running these tubes in anything but tetrode/pentode. Definitely can't go UL, or triode. A nice regulated screen grid supply should be pretty feasible, but personally, I'll stick with more known, more widely available tubes like the 6L6, even if it means more cost. If I had a bucket full of those tubes, for example, it might be worth some exploration.
 
I'm still experimenting but at the moment oh around 260 at both the
plate and the g2 with using UL taps and 30ma per tube, Push Pull UL.

Using ST-70 iron so 4300 p to p for the load.

This is very very early stages here but the sound is really promising.

I've allways been curious when they rate the G2 so low but yet in triode
the rated voltage is the same for the tube as the plate in pentode mode is.

One spec I found was 330 max plate voltage for pentode and same for triode.
 
I have a bunch of 6W6's, but haven't had the time to explore their limits yet. My experience with other tubes in general is that once you get above the maximum ratings each different brand or different construction version of the same brand will behave differently. Some tubes may get upset at being operated slightly above the maximum ratings, while other versions of the same tube type may smile at twice the maximums. This was very evident with the 6AV5's. Some began to glow at 14 watts plate dissipation, while the Sylvanias were well behaved at 25 watts. The same thing applies to screen voltage.
 
At the levels I'm curently at I see no signs a fatigue, but these are
not all that easy to tell with the darker glasses and the black plates.

I see no glow whatsoever though of the plates, but I'm also not really
pushing them as yet, that's if the triode conection data of 330v is good.
 
Allright today I got upto 355v on the plates and 33ma current draw for
a plate disipation of just under 12watts!

I was upto about 110 on the variac with the 5r4wgb rectifier in there.
Never got any funkyness on the tubes themselves but did get a couple
very small clicks/pops so backed it off then shut it dowm, I think I found
my answers and 330v UL with 33ma is about what I'd start out at trying
to run them if I was pushing them pretty good.

To bad the 5r4 didn't drop just a touch more voltage so I could actually
put the thing in the main system and not need a variac.
 
Allright I'm done tinkering for now, but when approaching 350v on the
plates the tubes do start to groan pretty much at any reasonable current.

So I think the 330v max is pretty darn close to where it's at, in UL that is
so I suspect the same thing for triode.

Pentode with a lower g2 voltage you could probably squeeze a bit out of them.

I will sometime down the road build an amp with these as the sound is excelent!

Nice and airy with a great shimmer but still has grunt at the same time though. :)
 
I am at work now, so I can't look at a 6W6 to see if there are any holes in the plates. I don't remember any. It is possible, and common for the screen grid to be glowing red hot and the plate to be normal looking. A tube generally will not life long if operated in this manner. Many sweep tubes have a low screen grid voltage rating (175 to 275 volts) while the plate voltage rating can be 550 to 990 volts. Many of these simply don't work in UL or triode mode because of this. I melted the screen grid in a 6CD6 at 350 volts, while several 6AV5's work fine at the same voltage.

Look carefully in a darkened room for signs that the grid wires are glowing. If they are, back off the voltage a bit.

Look at the idea shown here. This can be used with UL also to allow for a plate voltage that is higher than the screen voltage. I don't like the extra 1N914 diode at the bottom of the string, and it really messes up the works with UL. Replace it with a wire. Experiment with the number of zener diodes. More diodes allows more plate voltage, too many and they will stop conducting when the plate voltage drops on signal peaks causing some really nasty distortion. I even tried this with a gas regulator tube, but you need a lot of plate voltage, far more than a 6W6 can take.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=96649

I have been working on an adjustable screen voltage shifter circuit, but it is not ready for prime time yet. In fact it blows up a lot! It sounds cool when it works though, and I have run a 6CD6 in shifted triode mode at 555 volts, the limit of my power supply.
 
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