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136.1.1.109
In Reply to: RE: Eimac tetrode verses pentode in triode conection. posted by Al Noakes on April 11, 2014 at 02:40:59
I have been running 5-125B, and with 10V rigging to the filament Iron, 813's on AC with no audible hum on efficient speakers. One winding and one hum pot for each tube. They both run U-L at 20 or 30% on a 10k a-a OPT. I like the 5-125B slightly better, and they make me 60W in Class A from just under 600V.
They will shortly get their first modification; trading a 6H6/FQP1N60 cascode LTP for a pair of EL84...also rigged as LTP.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Follow Ups:
PP is a bit extreme for me. I have thought about it if you can get away with ac filaments it does not seem so extreme after all. For the record I am going to try 4e27 and a and the tetrodes and any other tube that I can run and listen for a while.
Tonight I have to think of a budget design for a amp.I have always resisted engineering amps. It occurs to me if I was comfortable with the technology it would be fun and rewarding to layback in bed on the lap top spicing your amp design trying tonnes of different ideas. More interesting then TV. If only? Lots of google spice for me to see if its tasty.
Gday Douglas
have you tried the cheaper (currently) 4d21 tube to compare?
Nah, not tried the 4D21 yet. I have not even tried boosting the g3 voltage( would probably try 9V with a battery for starters ). That one looks like it has potential, especially to firm up the knee at the upper left of the curves...which are dominated by the U-L percentage I happen to run.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Long time... You have the advantage of cancellation to keep your fils quiet but have you tried DC at all ? With SE I find DC is the only way.
Al
Never tried DC; never saw the need to go to all the trouble of rectifying and smoothing it...especially considering there needs to be 15A of it for two. AC did just fine, thanks to the cancellation you noted.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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