LA-2A point to point build Sowter TXF

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Spencerleehorton

Well-known member
Joined
May 12, 2012
Messages
4,031
Location
Felixstowe, Suffolk, UK
Hi guys,

Thinking about starting a point to point build of LA-2A using the Sowter transformers and the T4B.
Gathering up most of the caps and resistors and fibreglass board with turrets.
Not really understanding what is the NE2 cap which is in parallel with a 470pf cap from the output transformer?
Also looking into building my own T4B photocell unit if anyone has anymore help or documentation for this?
All help is welcomed in making this beast!!!

Regards

Spence.
 

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check out the thread called All thing la2a. All answers to your questions will probably be there :) by the way, I did 2 units with sowter. Cool transformers
 
Hi,

Yes, I like sowters, Brian Sowter is a few miles up the road along with where they are made!
Looking like I could do this build for about £250 as I have quite a few parts and I'm gonna make the pcb turret boards.
Will check that thread out thanks.

Regards

Spence.
 
Hi,

Have sorted TXF, terminal board, tubes, sockets, pots, Vu meter, caps and resistors. Making my own T4B and housing as it's pretty simple, just need to match photocells. Have output TXF just need to get Sowter input TXF.
This is a really exciting build and I'm looking forward to the frustrating parts!!
Also think about a having the T4B with more photo cells so I can switch between two different types to make the unit more flexible. Have one set fast and other set slower.

Regards

Spence.
 
Thanks guys, that's some gret info.
I was planning on doing two switchable  flavours for the T4B.
I am going to go with 230v x 115v toroidal and voltage doubling to get the 275v for HT.
I will get the 6.3v 2A AC from another TXF for the H+.

Regards

Spence
 
Go with a fix value. The vari cap is a arco 465. I goes with a 150pf in c4 and c14 is for the stereo link, so not really usefull if you dont want to link two in stereo. C14 could be 330pf. These are the values I put in all my la2a build.
 
Hi,

I am going with the variable capacitors first of all then will test and put in set value.
Also I am going with chameleon labs 7602 output transformer and Sowter 4383 input transformer.
Eventually I will change the output transformer for a Sowter 8940.

Regards

Spence.
 

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If i can suggest you one thing, try to separate as much as possible your power transformer from your other transformers and circuit. At least 6 inch. It's a good way to eliminate sources of possible hum :)
 
Hi,

Yes very good point, my audio transformers will both be over the left utilising the valve struts to help isolation. Going to try a few different input TXF as I have a few lying around to test the theory of this unit being compiled originally from bits just lying around. 8:1 seems correct for input TXF.

Regards

Spence.
 
Let us know about all developements :) there is some you can try, too. Replacing the plate resistor of the first 12ax7 from 220k to 100k and replacing the valve for a 12at or 12au7, dont remember. It increases a little bit the head room on the gain circuit, miking it more usable.
 
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