2A3 get*set*go docs

2nd harmonics for the masses

2A3 Manual Question.

Postby scalardia » Sun Aug 26, 2012 8:28 pm

Thank you, Shannon! I've completed GSG 6B4G project, tested great, now matching OTs for best sound, that's why I got some spare 6AX5GTs for next 2A3 project.

I'm going through 2A3 manual, one question: page 7, last line... "Solder a small wire from C12 positive to TP2. This DC biases the heater on the 6SL7." Please advise me where TP2 is in the PCB? maybe I overlook it, help me out. Thank you very much!
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Postby Shannon Parks » Mon Aug 27, 2012 4:54 am

TP2 is a test point for measuring the bias voltage of one of the power tubes. It is located near R16B and C6.

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Thank you!

Postby scalardia » Mon Aug 27, 2012 3:20 pm

Thank you so much! my eyes are too big to miss it...
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2A3 Filament Power Supply

Postby paul9000 » Thu Dec 27, 2012 3:30 pm

The July 2000 issue of Tube Cad Journal has an idea for 2A3 filament power here:

http://www.tubecad.com/july2000/page10.html

It needs rectified output from a center-tapped transformer of at least +4/-4 V. It uses the trick of an LM350 (+) and LM333 (-) to self-regulate at +1.25 V / -1.25 V when their Adjust pin is tied to Ground. There's no mention of whether or not the author built it or if he just thinks it will work.
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Re: 2A3 get*set*go docs

Postby EWBrown » Thu Dec 27, 2012 7:30 pm

I meant 45, not 2A3, must have been half asleep when I typed that one :$ ;) (lol)

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Re: 2A3 get*set*go docs

Postby Geek » Fri Dec 28, 2012 1:49 am

They're both little angels [:) (wine)
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Re: 2A3 Filament Power Supply

Postby Shannon Parks » Fri Dec 28, 2012 7:53 am

paul9000 wrote:The July 2000 issue of Tube Cad Journal has an idea for 2A3 filament power here:

http://www.tubecad.com/july2000/page10.html


Thanks for the link. I also like the section on lower tube filament voltages - nice to see it in a chart. Just ordered that book online.

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Re: 2A3 get*set*go docs

Postby vvelt » Wed Nov 23, 2016 1:40 pm

I've been looking on and off for the Edcor power transformer for the 2a3 build, and have sent numerous emails to Edcor about it. It doesn't show up on their website but a Google search did turn up a PDF doc on it, https://edcorusa.com/Content/Manuals/XPWR067_100-120.pdf. So I just called them and was told it's been discontinued, and if I really wanted it they would need a minimum of 5 units for an order. This stunned me since they're made to order anyway - something about the setup required to build it.

The alternative transformer from Hammond lists for $143 on Mouser, and provides less B+ voltage. I want to build this with a 5V4 rectifier.

Are there any other alternatives?

For the 2a3 filaments, can a 5v CT transformer be used for both tubes or would I need two 2.5v transformers?

Does anyone else want to go in on an order for the Edcor transformer?
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Re: 2A3 get*set*go docs

Postby Geek » Thu Nov 24, 2016 12:14 am

I designed the XPWR183-120 for this 2A3 build:
viewtopic.php?f=4&t=5769

Can you make it work?
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Re: 2A3 get*set*go docs

Postby TomMcNally » Thu Nov 24, 2016 9:19 pm

Gregg - that's the very one vvelt is referring to. It's not found on the Edcor site anymore and they want a minimum of 5. (???)
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Re: 2A3 get*set*go docs

Postby Geek » Thu Nov 24, 2016 11:11 pm

Oh! I thought his link was for the XPWR067, not 183 (???) :$
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Re: 2A3 get*set*go docs

Postby EWBrown » Fri Nov 25, 2016 1:52 pm

Each 2A3 would require a separate 2.5VAC, 3A filament transformer, unless you can find one which has two 2.5VAC, 3A windings.

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Re: 2A3 get*set*go docs

Postby TomMcNally » Fri Nov 25, 2016 6:57 pm

sorry Gregg ! You are correct, my Internet has been so slow for the last week or so I can't even download PDF's without a long wait and timeouts. The 183 you designed is very cool, but in the same boat as the other one, discontinued. It was my understanding that once they had a design, anyone could buy it, it was added to the line.

Ed - take a look at the XPWR183-120. Very handy for 2A3 and 45 amps.
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Re: 2A3 get*set*go docs

Postby EWBrown » Fri Nov 25, 2016 8:20 pm

EDCOR no longer lists the XPWR183-120 =:o
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Re: 2A3 get*set*go docs

Postby vvelt » Thu Dec 08, 2016 7:11 pm

Thanks to all who answered to help me figure this out. It looks like both Edcors are discontinued, there is also the Hammond 302AX. Is 600vac enough with a 5v4 rectifier?

I could go with separate 2.5v filament transformers. There is the Hammond 166L2 at 2.5volt, 2.5amp. They also list the 266M5, which I think can be wired for 2 X 2.5volt @ 3amp? Is one better than the other?

Going with seperate filamnets, should my main transformer have a 600v, 640v, or 660v secondary? One I found with 660v is rated at 140ma, is this enough current for the high voltage secondary? 

Thanks again to everyone for your input, much appreciated.
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