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Hi folks,I had built a 2A3 SE amp to drive a pair of Belle Klipsch and liked it a lot. I've switched to a pair of Harbeth Compact-7 and want to built a PP amp to let it sing.
I've heard both 2A3 and 300B SE amps and found them sonically charming but in different way, the 2A3 is more transparent and the 300B has more lush and a fuller bottom.
Anybody have experience with 300B and 2A3 PP amps? Which one is a better candidate for a pair of 86dB/W/m speaker? Built in AB1 specification, a 2A3 PP yields 15W while a 300B PP could give 18-22W. How do they compare in driving power and sonic characteristics?
Thanks for any input.
Follow Ups:
I have a pair of 25 watt PP 300B mono blocs that have not yet even come out of their boxes other than for this picture (right side). They started life as Ming-Da designed units that I was originally going to do some upgrades on. Now it has turned into a complete exclusive design where I will not even need these. I have not yet even plugged them in and have no idea how they sound. (this is not an ad as they are not for sale).
My intentions are to maintain the chassis as I find them a great base for my own new design. I will build both a PP 300B and 2A3 design that will also utilize the 2.5v 300B.While I have heard both 2A3 and 300B PP designs, I cannot say one is "better" than the other but will admidt I prefer the 300B which has led me on the path of my own design.
I would recommend listening to a few different designs before making any final decissions. Good luck on your journey and happy listening.
Hello,I'd stay with well executed, low DCR supplied, 2A3's, they sound GOOD, ( better than 300B's usually IMHO ), and you have to double the power to get a measily 3 dB increase in volume from the amp. The difference between 15 watts and 30 watts folks, is only 3 DB in loudness!!!
You want Class A triode to keep the distortion low over the
power range you need. AB1 is just a big step back in performance.
I think a 30W PP KT88 Triode amp might just barely do it. 86dB is
rough. Whats the impedance look like?For real triode power, unfortunately, you are talking big and expensive. PP 845, 813 and its ilk.
The SV811-3 was an exceptional product - when it was manufactured
for its brief time here.
HI Jim,
Let's not over look the 805 and 211 for big triodes. The 805 is a personal favorite of these large runway lights / whole house heating systems.
There are now many designs by various manufacturers that are utilizing these tubes.
Just to confuse you, how about a 40 Watt 2A3? See link below.http://www.jj-electronic.sk/pdf/2A3.pdf
I can only compare them to valve art ... nope. JJ are much-much better (and much more expensive).
.
Hi,How would one setup for class A? I am currently working on a PP 6b4g and am just curious as to the operating points for class A.
250 volts across the tube 60ma. of plate current per tube into 5K PP load.
Have Fun and Enjoy the Music
"Still working the problem"
Thanks for the response.Are these operating points for class A PP simply the operating points for Class A SE with doubling of zout ?
Not doubling the output Z. Doubling the load. Maybe that's what you meant. As long as you keep it Class A, each tube in a push pull circuit will see one half the transformers impedance. (The reason for this is highly debated, but the end result is not argued) So a 5K PP transformer will load each tube with 2.5K, which is testbook 2a3 (6b4g) loading.In the tube data, PP class A is not normally given. I think that's because they assume if you are going PP you want the extra power of Class AB. I think real Class A push pull sounds better, less distortion, no need for feedback to "clean up" the crossover distortion.
Push pull Class A will give only twice the power of SE Class A for the same tube used. The even harmonic distortion (if the circuit is balanced well) will be a lot less.Tre'
Have Fun and Enjoy the Music
"Still working the problem"
.
... Zout is halved (under some conditions) when 2 tubes are PP operated.
Hmmm - if PP 2A3s, which have a plate dissipation rating of 15 watts can put put 15W (common specification), how come PP 330Bs, which have a plate dissipation rating of 40 watts, can put out only 18-22 watts?
How about your question reversed:Given that it would be be fairly easy to get over 40 watts in class AB1 from a pair of 300Bs, why doesn't anyone think it's a good idea?
Because they've heard it?
Make everything as simple as possible but no simpler - Einstein
Actually, that is precisely what I am (had) running. PP JJ 300bs, 6.6K PP impedance, Vp = 425, Ik = 75 ma. But I have never measured the available output power because I don't have a way to measure distortion. Seems to me that a output power rating is rather meanigless if you don't state the distortion level.If PP 2A3s have acceptable performance at 15 watts why won't 300Bs at 25 - 40 watts?
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