LA-2A point to point build Sowter TXF

[Deepdark]

You can Check out my la2a builds on my personnal page. Maybe it could give you some ideas haha. www.facebook.com/elab.electronic

 

[Spencerleehorton]

little bit further

 

[Spencerleehorton]

Nearly completed wiring up!!

 

[Spencerleehorton]

only few bits to go now

 

[Spencerleehorton]

photocell boards

 

[Deepdark]

Let us know when you'll power it up.

 

[Spencerleehorton]

Hi,

Yeah, just 1meg pots, input/output sockets and input TXF to wire in then I'm ready to power up and test.
Have made four different T4B modules to test different photos cells and caps.

Regards

Spence.

 

[Spencerleehorton]

Hi,

Just 2 x 1 meg pots to go in now, check wiring and going to power u using variac so not to blow anything first of all.

Regards

Spence.

 

[Spencerleehorton]

Last bits!

 

[Spencerleehorton]

Hi,

Powers up, heaters work, no smoke just gotta test signal path.
At the moment has OEP A262A3E input TXF, but will change to Sowter.
Not proud of how messy this is but once all working will revise and neaten up.

Regards

Spence

 

[Deepdark]

I highly suggest moving your output transformer from you PT. You risk to run in some hum trouble (maybe not, though). At least 6inches

 

[Spencerleehorton]

Hi,

I am going to redesign the whole thing as it's not playing ball!

Spence.

 

[Spencerleehorton]

Hi,

Gonna implement another chamber in the case for housing the components separated from the transformers and the tubes.
I have planned then to stick to short wires from tube sockets to the components.
This should greatly improve overall screening and stop interference.
Power transformers I will keep as far as possible away from audio transformers.
Also going to change 220k resistor and go over to 12at7 tubes for higher head room.

Regards

Spence.

 

[Spencerleehorton]

Hi,

This is the revised layout And should work as intended.

Regards

Spence.

 

[Spencerleehorton]

Hi all,

Having some trouble getting the EL panel working, I am getting 128v before the 0.01uf cap to pin 3 on the T4B but not getting anything from the EL panel?
Within the T4B I am using a 0.01uf on pin 3 down to gnd but not put in the 2.2meg resistor, does it need the 2.2meg resistor to work?
I have several of these el panels and would like to test they work.

I am getting an input and the audio path to output works, wave form looks a little weird on the output though.

All help is welcomed is getting this bad boy going.

Regards

Spence.

 

[Spencerleehorton]

Hi,

Just wanted to clarify on a couple of points:

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.

You have said C4 and C14 should be 150pf but then said C14 should be 330pf?

I have some mica 330pf and I'm not using the stereo link function so have not included this bit in the circuit so C14 is not needed.
Should C4 be 330pf?

Also using the 12at7 tube is it changing R9 and R13 from 220k to 100k you mean?

Regards

Spence.

 

[Deepdark]

The c4 should be everything between around 150 and 330. C4 150pf result in a better bandwidth, if I remember well, than 330pf. The goal here with the vari cap is to put the unit on an analyser, feed it with a signal and adjust c4 until you get the better response possible. In most case, the value ended up being around 150pf. But if you just have 330pf, you can go with it and change it latter. Looking at the tubes, you can replace the tubes and keep the 220k. Replacing them result in some more headroom.

 

[Spencerleehorton]

Hi,

Any idea why I can't get this EL panel working!!!

Regards

Spence.

 

[Deepdark]

do the signal pass through it or not? Is it just not compressing?

 

[Spencerleehorton]

Hi,

I have now got a setup which tests the EL panels and measures the photocells so to match them.
All good, I had the EL Panel the wrong way round!!!
Stay tuned for the next installment, hopefully more good news to follow.

Regards

Spence.