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On 7-6 robertpeterson56 asked about using the 6AV5 strapped as a triode but was concerned because of the low g2 rating of 175V. In the discussion that followed, one suggestion was to tie G2 to the cathode instead of the plate. There was speculation that this wouldn't work but nothing definite. The curves in the 6AV5 info I have only go to 75V and plate current is really low at that point.Since then I've played around with a 6AV5 strapped both ways and can report the following:
1. Strapping g2 to the cathode indeed doesn't work. With 0V on g1 and 400V on the plate, plate current was just 10mA. g1 would need to be driven + for any appreciable plate current and I doubt that it was designed for this service.
2. Strapping g2 to the plate (thru a 1K stopper resistor) seemed to work well as a triode. I ran this up to about 350V with appropriate g1 negative bias and nothing let go. As a result, I'm reasonably confident that the 175V g2 rating is very conservative and can be disregarded for conventional triode strapping.
3. The 6AV5 appears to be one tough little tube. I ran it as a triode @ 350V with combined plate/g2 current ~60mA for about 5 min. There were no red spots on the plate or glowing g2 wires that I could see. This is 21 watts for a tube with a combined plate/g2 rating of 13.5 watts...not bad!
4. I set up the triode strapped 6AV5 at a couple of operating points specified for the 6B4G (g1 V & plate V) and compared resulting plate current. Surprisingly, the current was reasonably close to what was specified for a 6B4 under these conditions. Obviously, a couple of points is not a set of curves but I believe there's more than coincidence at work here. Maybe Sylvania or whomever was justified in using a triode strapped 6AV5 as a modern day replacement for the 6B4G in govt apps. Wonder if discerning ears could tell the difference?
5. The 6AV5 absolutely requires G1 and G2 stopper resistors when triode strapped to prevent oscillation. I initially set up w/o them and ended up wiping out the lower end of the FM band as I powered the thing up. Position of my had around the tube changed the frequency.
Bottom line: The 6AV5 and possibly other neglected TV sweep tubes are probably worth pursuing as triode strapped audio output devices. g2 voltage ratings can probably be uprated to reasonably high plate voltage say on the order of 350-400V w/o failure (triode service only).
AS always, YMMV, so do your own homework!
Follow Ups:
"4. I set up the triode strapped 6AV5 at a couple of operating points specified for the 6B4G (g1 V & plate V) and compared resulting plate current. Surprisingly, the current was reasonably close to what was specified for a 6B4 under these conditions. Obviously, a couple of points is not a set of curves but I believe there's more than coincidence at work here. Maybe Sylvania or whomever was justified in using a triode strapped 6AV5 as a modern day replacement for the 6B4G in govt apps. Wonder if discerning ears could tell the difference?"Keep in mind that real 6B4Gs vary from the nominal spec too. There's a wide variation in what the actual tubes perform at vs. spec. So a 6AV5 that's close would undoubtedly work fine. Tone quality? I don't know, never heard one...
Hi,Intereting you did try (1) :-)
There is no tube I know of that is designed to work that way.
You didn't try to dial up B+ even more?
Thid you read the "S" value (transconductance)?mvh /Pär
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Me fail english, thats unpossible!
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The deHavilland 845 amp uses the 6AV5GT in triode. Prior versions
of their amp used new production 6L6/5881/KT66 stuffs. So, if deHavilland is using this tube - something is sonically jiggy
with it. ;)The 6W6GT is also a TV sweep tube. Strapped as a triode it is
THE BOMB. Read the whole link below for the tip-off. I'm using
these for my own 845 amp and it outpaces just about everything. The
closest best thing is the Saratov KT66, triode strapped. The Saratov
is 10x the price. :)There are other triode-oriented sweep tubes, the 6BX7 was one,
the 6EM7/10EM7 is another one. ;)-- Jim
I have a bunch of 6Y6, which have a good reputation in UL but haven't stirred much interest as triodes. Can anybody report on how they sound in triode, and what HT to use? The screen is rated either 150v or 200v in different data, so I'm assuming 250v max in triode.
Such as the 6BL7/6BX7 which are genuine triodes, and the ubiquitious 6AQ5/6BQ5/6V6, all of which respond well to triode strapping and are "tried and true." I guess if someone has a bucket o' 6AV5s, that's one thing, but the other tubes above are also inexpensive and there's plenty of prior art to get one started.
...As per original post. BTW, to me "sweep tube" means horizontal output although I suppose vertical output tubes you mention are sweep tubes too.A lot of sweep tubes have plate dissipation ratings that far exceed the ratings of the true triodes you note. They're also usually designed for HUGE peak current capability. Just look at the size of the cathodes and the filament power requirted to heat them. I'm not sure of the audio implications of high current but if nothing else it's reassuring.
One other point is the cost of these tubes. The really high power capability versions are coveted by linear amp users (illegal CB ??) where they're run well above ratings. Since they don't last too long in this service and most linears use multiples of them to get high power, the demand is relatively high so prices are too (6LF6 and 6KD6 come to mind). The lower power versions are usually dirt cheap
At the end of the day, there certainly are easier tubes to use for audio but this being DIY, isn't that part of the challenge?
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