JE Labs 2A3 amp: work in progress...finished!

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Finally got everything, except binding posts, mounted and ready to solder. Those Hammonds are rather unsightly, but the amp looks alright overall. Here are some pictures:

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No change from the original schematics, save no electrolytics in the PS. I can't wait to hear those 2A3s with those hefty James irons.

[Slartibartfast]

Looks good.

Did you use a unibit or a punch set for the socket holes. I like the ease of the unibit, but I do not havea drill press. The punch looks like it might be easier to freehand than a drill and unibit.

Robert

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I used all three. I first drill a small pilot hole with a 3/32 bit, after which I drill with a unibit to make another 13/16 piolt hole for my punch screw to go through. Then I have an option of punching holes of different sizes. I am not aware of any unibits that would drill hole bigger than 1". Perhaps there are such unibits, but I haven't seen any. I use a unibit (7/8" step) for 9 pin sockets.

I am sure this is not news to anyone, but I realize that it works far better to first drill at lower rpm to prevent the drill from figure skating around the surface. Also, I find that pushing too much while the drill is reving up too high causes the bit to get stuck in the hole. Yes, I had to learn this the hard way.

[Slartibartfast]

You can get them up to 1 3/8" hole size. To keep the bit from skating, I use a a punch tool to make a small dimple to keep the bit in place.


What size hole did you cut for the 2A3 sockets?

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I got it finished last night. It took some work, mostly because I wanted it done right. I hooked it up and worked great the first time. I was kinda diasspointed as I didn't have to do any troubleshooting. How does it sound? One word: wow! There is so much depth the the sound overall. Maybe it's those heavy irons. And yes, the thing weight at least twice as heavy as my ST-70.

I have a pair of aluminum housed 25W resistors for 2A3 cathodes coming, so I will replace those 10W resistors. No smoke from them, but they do run kinda hot. I went with no electrolytics in the PS. I really dig those fat 18K gold binding posts I got on eBay. They are only 10 bucks for two pairs. Anyway, here are some pictures of the finished product:

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Those 2A3 holes meaure 3.5 cm.

[TomMcNally]

Great looking amp Min !

Those James transformers look great.

One tip - the standard binding post spacing is 3/4"
so the dual plugs will fit. If you do 4 and 8 ohm,
put the black in the center and a red 3/4" on either side.

[Slartibartfast]

Looks great! Mine is on hold as I have to spend a week going for a network certification class. Yellow_Light_Colorz_PDT_21

What rectifier tube are you using and what is the voltage difference from the listed voltages on the schematic?

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Thanks, Robert! I am using a 5Y3. My B+ is around 375 VDC with and around 360 VDC at the plate. I have a thermistor installed, which helped lower the voltages a bit. I am probably ok with those robust Sovteks, but I might run into problems using NOS tubes. The original schematic has B+ at 350 VDC.

Thanks for the tips, Tom. I will keep that in mind if I have a need for dual banana jacks.