so i am a novice amp builder and i need some schematic help. i found a very old school se 2a3 circuit thst seems like it would be a cheaper amp of 2a3 caliber to construct. although there is a couple things i dont understand. there is two circled capital "A's" and i have no idea where they go to. do they just connect to eachtoher??? also there are two wires named "Bch" that i have no idea where they should go to. there are also what appears to be two ground points and i need some guidance there as well. any help is greatly appreciated 
It's not gonna be any cheaper than any other 2A3 amp. The main costs are the power and output transformers(and in this amp the tube itself). Edcor has quality transformers for reasonable prices..anything more fancy is gonna cost more. (Edit: and the choke too.)
Yep,the two circled "A" points connect together.
The two ground points are connected together.
"Bch" goes off to the "B-channel" IE,the other stereo channel. The schematic only shows one channel to save space,since they're identical.
Yep,the two circled "A" points connect together.
The two ground points are connected together.
"Bch" goes off to the "B-channel" IE,the other stereo channel. The schematic only shows one channel to save space,since they're identical.
I wouldn't build it. That design is hideous!
The 6SL7 does not make a good SRPP, and it's not very linear with Vpk< 100V. Judging from the 4K7 cathode resistors, the 6SL7s are operating at plate currents of well under 1.0mA. I did a design with 6SL7s, but as an LTP, and with Vpk= 120Vdc. That way, I got good performance, but I also included grid drivers that had a much friendlier load for the 6SL7 -- a low current, high gain triode that gets its high u by driving up rp.
The current sourcing isn't there for driving the grids of a 2A3, so that will have slew limiting at the higher frequencies.
There are better 2A3 SET designs out there.
The 6SL7 does not make a good SRPP, and it's not very linear with Vpk< 100V. Judging from the 4K7 cathode resistors, the 6SL7s are operating at plate currents of well under 1.0mA. I did a design with 6SL7s, but as an LTP, and with Vpk= 120Vdc. That way, I got good performance, but I also included grid drivers that had a much friendlier load for the 6SL7 -- a low current, high gain triode that gets its high u by driving up rp.
The current sourcing isn't there for driving the grids of a 2A3, so that will have slew limiting at the higher frequencies.
There are better 2A3 SET designs out there.
I find these to sound excellent, but if you're looking for a more typical 2A3 sound, these aren't it.
Electra-Print.com 2A3 DRD Amplifier
Boozhound Laboratories
http://home.earthlink.net/~jeremyepstein/freelunch.html
An analysis using a 300B:
SPICE Analysis of Randall 2 DRD Amplifier
Well thanks hobo king. the boozhound laboratories schematic looks prrrety good
do you have an idea of budget?
as digitaljunkie noted above, the biggest portion of cost of a "decent" or even "cost effective" DHT amp ( 45 /. 2A3 / 300B, etc) will be the iron, particularly if you elect for choke filtering.
second the suggestion of Electroprint 2A3 DRD circuit
there's also the Bottlehead Stereomour kit - to give you an idea of budget - about $750 US
OK, I don't mean to be contrarian, but there was a very popular and quite expensive commercial SE amp that used a SRPP 6SL7, RC coupled, to drive a 300B. This amp went through several iterations and was written up in all the glossy magazines with glowing reviews and really was the amp that started a successful career. So I think it is a little disingenuous to assert that the topology is "hideous".
Personally I think that a direct coupled amp where the voltages need to be juggled to get them to work out correctly may be too much of a challenge for a novice amp builder. Someday I would like to build this or the 12AX7 version of the Loftin White just to see what all the fuss is about. It seems reasonable to assume that since the topology has survived the test of time and has been built hundreds of times all over the world that there must be more to it than the schematic would leave one to believe.
For now though I am happy to listen to my monkey/drd amp with its high transconductance driver tube.
Personally I think that a direct coupled amp where the voltages need to be juggled to get them to work out correctly may be too much of a challenge for a novice amp builder. Someday I would like to build this or the 12AX7 version of the Loftin White just to see what all the fuss is about. It seems reasonable to assume that since the topology has survived the test of time and has been built hundreds of times all over the world that there must be more to it than the schematic would leave one to believe.
For now though I am happy to listen to my monkey/drd amp with its high transconductance driver tube.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.