Radford STA 12 Rebuild

[snowman_al]

A day off from Christmas prep today, so spent a little time populating the Radford boards. And re-doing the valve holder rails.





I've also made a small bracket to mount the 35mm reservoir cap correctly, so I'll do a picture of that next time.


''What are the central spigots for on the small valve holders?'' They are needed as common ground locations for several components (and maybe add a little shielding) round the EF86.

''Alan, you didn't work for Marconi in a former life did you?'' No, though I did visit the Chelmsford site a few times. I worked for Burroughs Machines in the late 60's then for Xerox from 73 to 2001.
I just like to get everything 'tidy'. (OCD?)

Will says he may be able to provide a couple of later output transformers, so fingers crossed.

[snowman_al]

Well it has been a little while since I made any progress with the old STA12, but a couple of weeks or so ago Will sent me a brand new pair of output transformers for my amplifier. So many thanks to Will, and time to re-start the rebuild...




The new transformers are slightly larger and heavier than the originals fitted, but fit the original footprint with just a little elongation of their mounting holes.

Now a design / engineering problem of the original STA12 needed to be corrected. Difficult to see from pictures, but everything on the STA12 is thinner and lighter than the STA15.
Especially the chassis plate, where the transformers and choke fit, which is tinned mild steel and only has the folded edges to add any strength. This is how mine looked when it arrived... In fact all of the pictures I have found of STA12s exhibit a sagging top plate.




I added a couple of aluminium angle braces directly under the edges of the plate like this.




Now with the transformers mounted, time to add a bit of wiring back in. The chassis ground / earth post, centre/bottom, is a bit busy with 13 connections!




And on top.




And a few more pics here: https://photos.app.goo.gl/rPJOEbrehSVqL1l12

[walpurgis]

Going well there Alan. The bracing angles were a good idea. I'm looking forward to seeing how this turns out.

[Barry]

Beautiful work done there Alan. Well done!

[struth]

Bravo... Top Job

[Radford Revival]

Great job, glad to be of assistance with the OPTs and happy it all worked out

[Firebottle]

Superb job Alan, that must have taken a good few hours (weeks?).

Another thumbs up for Will Great to have such committed engineers on AoS.

[Cycleallday]

Another well documented rebuild Alan.

Your care and attention to detail is amazing - most would be rushing to get the job done rather than doing it properly.

I'm still enjoying the World Designs KEL 84 you rebuilt and documented in the same manner as this.

Mel

[JohnJo]

Great to see another of these superb amplifiers resurrected and good for years to come. The Radfords really do seem to be an amp for life as they are so serviceable especially with Radford Revival on hand. Really good stuff