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In Reply to: RE: Screen Voltage - 6L6G/A/B & 6P3S-E ? posted by Triode_Kingdom on May 01, 2017 at 11:16:32
Guess I'll regulate the 6L6 screens to their recommended voltage like Eli suggested. The amp previously used 7355s, so the power supply wasn't designed for significantly reduced screen voltage. Wish I knew more about the 6P3S-E. It seems to be more robust, but I don't have any definitive information regarding the real screen voltage limit.
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Buy Chinese. Bury freedom.
Follow Ups:
"The amp previously used 7355s, so the power supply wasn't designed for significantly reduced screen voltage. Wish I knew more about the 6P3S-E."Given the sort of O/P "iron" used with the 7355, adding a filament trafo and switching to EL34 category "finals" might be the way to go. Hey New Sensor, the 7355 is yet another type to bring back from the dead.
I believe the 6П3C-E (6p3s-e) is a solid 5881 equivalent, which is not quite up to 6L6GC capability.
Eli D.
Edits: 05/02/17
Eli, I agonized over that decision a long time. The EL34 is technically a better match for the OPT Z. However, I think the "benefit" is only more output power than the OPTs can handle (original rating 20W/ch continuous RMS).
I did build up a channel using 6L6GBs, and the result was very good. Output power is a tad less than with 7355s, but distortion is better. THD at ~4W is 0.05%, IMD is 0.18%. The 7355s measured 0.12% and 0.59% for THD and IMD respectively. At 20W, the manufacturer's THD spec is <1%. I measured 0.54% with 7355s, and 0.4% with the 6L6GBs. The latter is a minor difference, but the improvement at lower power levels is meaningful. So, all things considered, I think 6L6s will be a good choice for this amplifier. I just want to be sure my NOS tubes last a good, long time. :)
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Buy Chinese. Bury freedom.
Years ago, ran the 6s3p-e ultralinear and in triode mode in modified ST-70s, best tube we could find for these amps bar none. By ear, we liked them at 21 watts dissipation, and they have held up well over the years (more than 10), and they are still happy.
The Russians underrated their tubes considerably. Have seen posts where they had ~ 600V on the plates and were still not red plating (no info on the screen voltage). As far as the screen voltage limits, I have run these puppies in triode mode at 440V, and have held up very well over time. Similar voltage in ultralinear, so the screens were pretty close to that voltage. I don't judge things as much as you do by the numbers, but I can say these are really tough tubes, and sound great. Worth a try.
twystd
Yes, I really like the 6P3S-E, and I have a large stash. However, in initial tests some time back, my prototype amplifier with ~400V on the anodes performed better with a 6L6GB. Output power was about 20% greater, and distortion was much lower, about 1/3 as much at output levels below 5W. This might be due to the anode voltage of the amplifier (most users operate the 6P3S-E well above 400V), or maybe the low-Z output transformers (~3.8K P-P). Whatever the reason, the 6L6 types were clearly superior in this application. This is what led to my question regarding screen bias. At the time of the tests, the screens were operating through a dropping resistor at roughly 360V. There wasn't any damage to the tubes that I could detect, but I don't think it's a good idea to operate this far above the rating. I have uses for the 6P3S-Es later, but for now, I just wanted some idea of how others are using the 6L6.
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Buy Chinese. Bury freedom.
Edits: 05/03/17
Sounded the best biased to 5881 parameters. I ran 460-470VDC on plates and changed the screen grid resistors from 470ohm to 1k-ohm, 5-watt. Set idle bias dissipation to 15 watts (66% of 23 watt max), in a silverface Fender Bandmaster amp.
If I ran at 66% of 30 watts, 6L6GC standard or 20 watts, the amp overdrove too early in volume range. And had a much more compressed tone.
These are good tubes, if set to 23 watt max limit.
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