Opinions on 6L6 as triode

[Jazz P Bass]

I experimented with JJ 6V6S. I got lower power than two others I have. I did the power test on my amp, I never manage to get above 19W out of it. But just by changing to even the cheap Ruby tubes, I got 22W or more. I never understand why. I used resistor load, driving to clipping to measure the peak voltage. Everything else is exactly the same. The plate voltage is slightly over 400V. So I think I was comparing apple to apple.

I use a 150mA PT and OT of Vibrolux, these are good for at least 30W. So the limiting factor got to be the tube.

Sounds like you got tubes from the low end of the production bell curve.
Ruby would rate these as 'soft/ cushy tubes' no doubt.

[Leo_Gnardo]

Sounds like you got tubes from the low end of the production bell curve.

(playing to the JJ bashers): how astonishing!

Ruby would rate these as 'soft/ cushy tubes' no doubt.

Unlike (old) GT, and several other distributors, Ruby doesn't tag their tubes with such descriptions. Like some of the better distributors, they simply put emission & gain data on from their test rig. Granted, some shaking-about in transit can skew the tight matching of a set that starts out all the same emission within a milliamp. If you have amps that require output tubes with emission near the low or high end of the scale, you can order 'em that way. Helps save me a lot of headaches replacing EL84's in Voxes & similar self-bias amps.

Antique/CE, Tube Doctor, Doug's Tubes (and maybe others) also provide tube sets closely matched with their test rig data tagged on the box or on the tube. I doubt all of them use the same test parameters but they're still a better bet than the current GT or just crossing your fingers & hoping for a good match.

Here's another odd but useful item: Doug's and Antique/CE both sell Ruby tubes, and they go the extra step of re-testing and matching. Good for those who 1: like the double-checked belt & suspenders approach and B) if you're an individual not a biz; Ruby sells to repair shops, manufacturers, stores & resellers like A/CE and Doug, but not to the general public.

[Jazz P Bass]

Sorry about that Chief.



I do believe I was thinking of the old Groove Tubes labeling.
Not Ruby.

[Mick Bailey]

I have seen 220 ohm screen resistors on 450 volt amps in triode mode.

220 ohm is quite common, even 120 ohm. The purpose of having a resistor at all at that value is to prevent self-oscillation which can occur in a 6L6 if the screen is directly connected to the plate, rather than to reduce the screen voltage. If B+ is already to high to safely supply the screen that's when increasing the resistor helps, though I would rather reduce the B+ and keep the resistor value on the low side rather than go higher.

[Alan0354]

Agreed, your test method looks fine to me. 19W vs 22W, just a pinch of difference, hardly audible. And I woulnd't fault you for preferring the non-triode circuit. For me, gotta keep the crustomers satisfied. Some want vanilla, others chocolate, and yet others a scoop of each.

Yep, I can only speak for myself. I had that in my "former" Marshall JCM900. Ha ha, it is no more, I ripped everything out, even the transformers!!!

I was surprised about the JJ. It is supposed to be higher power than all the other 6V6. It is almost the size of a 6L6 and it clipped so soon. Maybe it's the bottom of the bell curve like P Bass said, but I got the power out from another pair, so I am good. I do like their 12AX7.

Edit:

Come to think of it. Maybe the JJ is designed for higher plate voltage. Maybe if I raise to 420V instead of 405V, It might give more power while the other smaller 6V6s flame out.

[stokes]

I dont think the JJ's are so much "higher power" as much as just being able to take higher plate volts.I dont have much experience with the JJ's.Once a client wanted them in his Brownface Deluxe,they sounded like ass so I talked him into a pair of Marconi 5871's.He bought the JJ's because he thought the Deluxe put too many volts on the plate,he had it confused with the Blackface,and JJ touts theirs as being able to take higher voltages.

[Alan0354]

Funny, I kind of feel the JJ didn't sound as good. But the difference is so small that it's not a factor in my decision. My impression was it sound's kind of in between the 6V6s and 6L6. But again, the difference is very small.

Anyway, my second amp is based on EL34 that I like better, so it's EL34 for me. I keep the plate at about 410V and get 33W out of it. That's my target power for amps as 20W is a little low and 40W is on the high side.

[Tony Bones]

I've run 6L6GT triode without screen resistors without anything bursting into flames. So long as you're not running too much more than 400V it should not be a problem.

In the end, you really should just try different values and see what you like. How hard is it to tack a resistor on a tube socket? You don't need to twist the leads all around. Just tack it in place.

[Leo_Gnardo]

Come to think of it. Maybe the JJ is designed for higher plate voltage. Maybe if I raise to 420V instead of 405V, It might give more power while the other smaller 6V6s flame out.

FWIW I've seen 6V6 JJ's perform just fine in situations that ate up EH/fakeTungSol 6V6's.

Tony - I wouldn't expect any pyrotechnics from lack of screen grid resistor, just a reduction in tube life. I figure if you can put in a couple resistors & stretch extra months/years out of a set, that's a good bargain.

I've seen recommended but haven't done - screen grid resistors from the OT primary taps in ultralinear setup.

[Tony Bones]

Tony - I wouldn't expect any pyrotechnics from lack of screen grid resistor, just a reduction in tube life. I figure if you can put in a couple resistors & stretch extra months/years out of a set, that's a good bargain.

I don't really expect fire either, I was just having fun. The fact is, screen resistors do affect the sound; they provide local negative feedback much like an unbypassed cathode resistor. If I try different values and prefer the sound with none, then I'm going to leave them out. I'm not interested in hypermiling tubes.

[PeanutNore]

My Special 6 is modded for a 6L6GC, and definitely sounds darker in triode mode. In practical use all this means is that I find my tone at a different spot on the tone knob - it isn't unusably dark or anything. Triode mode connects the screen to the plate through a 5 watt 470 ohm resistor, but the plate voltage on that amp is only 350v, so the resistor is probably not really that important. I might try bypassing it and see if it affects the tone.

[Pedro Vecino]

The only two models that I have found true utility of triode mode have been the Bogner XTC with EL34 (fitted originally) and Fender Supersonic. The latter is an amplifier with a very lively and electric sound. Of course involves different eq settings to compensate for the selected mode, but very useful to give an appreciable touch of warmth without spoiling anything. Especially at low volumes.
In the other cases I do not see much interest.