|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
24.184.41.88
Using the JJ 2A3-40 in a DIY PP amp seems an attractive choice. 2.5 volt filament can operate at AC without hum issues in PP plus using fixed bias allows filament CT winding to be grounded. 40 watt plate appears to allow some good power output.
Can I operate these tubes at 325 volts on the plate and bias to 70ma? Should produce about 20 watts per channel in AB1.
Follow Ups:
Its a very nice sounding tube, I'm running mine at about 60 ma and 7 watts on a 5K SE OPT. They should last forever at this operating point.
If the 2A3-40 is truly a 2.5V 300B, you could get 18 Watts out as a single ended amp... (450V, 80mA, 2K load)
You'll run the 40 Watt tube at 36 Watts, but you'll only need to buy one pair of tubes. The real trick will be finding a 2K single ended output transformer that's decent. Magnequest may be able to make a DS-020 for you.
325V/70mA seems barely worth it, unless that fits an output transformer you already have.
"If the 2A3-40 is truly a 2.5V 300B, you could get 18 Watts out as a single ended amp... (450V, 80mA, 2K load)"
Using the same Western Electric chart you refer to above, I notice that at normal operating conditions for a 2A3, e.g. Ep = 250V and Eg = -45V that the 300B will pass 80mA of plate current while we expect 60mA from a 2A3. This leads me to believe that the JJ 2A3-40 is a 2A3 with a big-ass plate; not a 300B.
Since JJ makes a 300B as well as a 2A3-40, why not just use the JJ 300B if more power is needed?
I prefer the 2.5 filament and the 2A3 grid structure.
Well, the JJ 2A3-40 is a great tube and I like the possibility to run the tubes a little hotter than the traditional 2A3 without worrying about burning them up.
I have been building a pair of 2A3 PP amps for a couple of years. They will use the same operating point as my SE JJ 2A3-40 amps: 290V @ 60mA. The SE amps make a solid 2.5W and I expect the PP amps to put out about 8W, maybe 10W at 5% distortion.
Very well thought out schematic at least IMO.
6J5 in Sylvania round plate- known as good sounding tube.
46 triode driver- also well known as a great driver- some state better than a 45!
Excellent rectifiers with low resistance and does not break the bank
Tango NC-14- yes.
Just a well deigned amp in my opinion. Thanks for sharing.
I can't take credit for the topology as its inspiration was the 'Feral Eye' published in Sound Practices issue 14 written by Herb Reichert way back in 1998. It is embarrassing to note how long I have had these transformers, but I built single ended amps for a decade before getting back to PP.
BTW: the first tube can also be a cylindrical plate 6P5 running about 5mA.
My favorite 6P5GT is Tung Sol
BTW- The extra winding at the 45-5 output transformer. A form of cathode feedback? I find this very interesting.
Should work fine. As these are really 2.5 volt filament 300b tubes, the 20 watts output should be obtainable. 14 watts or so for real 2A3s.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: