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Another 2A3 build

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Here are a few pix of my Stereo 2A3 amp. The small foot print, is very heavy, about 50lbs, it is like picking up Lead or Gold, but in this case Iron.

Iron is from Edcor. 6SL7's and 5V4 are NOS US tubes. 2A3B's are Shuguang single plates.


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I do not have a schematic drawn, but will draw one up and post in the next day or so.

Here are the Edcor model numbers used:
Output transformers are - CXSE25-4-2.5K
Power transformer is - XPWR118-120

For the money, the Edcor output transformers are definitely the "best buy". They have great low end extension and good high frequency response. My measured frequency response (-3dB points) is 7Hz~22.5kHz.

There was a strange low frequency anomaly (+ 0.5dB bump) between 5Hz and 20Hz, so I formed a low frequency cut-off with an input cap that brought my frequency response up smoothly starting around 7Hz.

I'll post a FR graph (with and without input cap) for comparison for those who are interested.
The top chassis is painted with black wrinkle paint, which can be found in the paint section of your favorite automotive parts store. The trick to getting a nice "wrinkle" is to place it in the oven at about 170F for about 10 minutes, then take it out and let it cool slowly. I suggest you do this when the wife or girlfriend is out of the house for a few hours because it will definitely smell up the house. Then when she comes home and asks what that smell is, you can say that you had the front door open and the fumes must have drifted in.

The bottom chassis is painted with bronze Rust-Oleum Hammered. The end bells on the transformers were painted with Hammered Verde Green. (I guess the marketing genius at Rust-Oleum did not know that Verde is Spanish for "green", so in essence, they are painted "green green")

The chassis was previously a telecommunications piece of equipment of some sort. I bought the steel chassis at a local government surplus store for like $5 years ago.
I like the old Hammond transformer stickers that are stuck to the counter top's edge - it adds a nice touch. ;0)

Rgs, JLH

Memorabilia... the 1627SE stickers are from the first 2A3 amps I built back in 1999 and the 726 stickers are from my 211 mono blocks built in 2001. One of the power transformers in the 211 developed an issue, so I bought a pair of 726's, as replacements, last fall.

I recently found the stickers and stuck them on the bench.
That's very nice and neat work! I like it. It's curious how the 2A3s look similar to 300Bs at first glance. It looks like the two motor caps on the top are a tight fit through the chassis with some kind of sealant around the bottom edge. Correct? Never saw that before. And the circuit, I can see it in my head by studying the bottom picture. (Paralled 6SL7 sections cap coupled to the self-biased 2A3)
Here is the schematic. A break down of the parts I used is as follows:

Cathode / Input resistors - Dale RN60D type metal film
6SL7 plate resistor - Carbon or Metal film (Can't remember where I got them from)
0.25uF/600VDC coupling cap - Mallory "Orange Drop" type
2A3 cathode resistor - Ohmite Wirewound Ceramic 25 Watt
2A3 Bypass cap - 100uF/100VDC non-polar IC type (Illinois Capacitor)
Oil filled PS caps - ASC type motor run cap (but not ASC)
Decoupling PS caps - 10uF/450VDC (generic brand)
2.2k decoupling resistor - Carbon film
6SL7 sockets - NOS Amphenol
5V4 socket - NOS bakelite
2A3 sockets - Chinese ceramic
100 Ohm hum bucking rheostats - Ohmite 12.5 Watt


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