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Old 13th July 2011, 09:30 PM   #1
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Default simple se 2a3 amp help!!!!!

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
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Old 13th July 2011, 10:17 PM   #2
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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.
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Old 13th July 2011, 10:19 PM   #3
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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.
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Old 14th July 2011, 04:37 AM   #4
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Oh thanks digitaljunkie! I will def take into consideration using Edcor transes in the future. But apparently my greenhorn status has led me to a less than ideal schematic as pointed out by miles prower. Oh well. Thanks for the help!
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Old 14th July 2011, 04:40 AM   #5
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Quote:
Originally Posted by Miles Prower View Post
I wouldn't build it. That design is [i]hideous[/

There are better 2A3 SET designs out there.
Well is there a schematic that you would recommend??
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Old 14th July 2011, 03:00 PM   #6
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Originally Posted by bignickthegreat View Post
Well is there a schematic that you would recommend??
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
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Old 14th July 2011, 04:02 PM   #7
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Well thanks hobo king. the boozhound laboratories schematic looks prrrety good thanks for your help
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Old 14th July 2011, 08:20 PM   #8
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by bignickthegreat View Post
Well thanks hobo king. the boozhound laboratories schematic looks prrrety good thanks for your help

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
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Old 14th July 2011, 08:31 PM   #9
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Here's the one I built, I like it a lot.
Others who are more knowledgeable can say how it compares to other designs.

6C6-2A3
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Old 14th July 2011, 09:15 PM   #10
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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.

Last edited by Palustris; 14th July 2011 at 09:20 PM.
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