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Radford STA15 Restoration.

snowman_al

snowman_al

pfm Member
I collected a new toy yesterday.
A really cosmetically challenged Radford STA15 III. Been in a damp shed for a while apparently.
But all original and never repaired as far as I can see. The caps are dated December 64 and January 65.
The valves are all yellow label Mullard except for the Mazda GZ34 (which was a Mullard f32 from '64).
Unfortunately it and one of the ECF82s were dead, still could be worse.

I could not resist a quick vacuum out of the dust and spiders. Checked the transformers were okay and ran it up slowly to 240 volts and nothing went pop even with the 'Silicon GZ34' in.
So I popped the valves back in (and a new ECF82) and was greeted with one channel working and a lot of crackling from the other.
A quick fiddle with the valves and the culprit for the crackle is a very poorly phase splitter valve socket, but with the valve at an angle (!) it comes to life in Stereo. That was an hour or more ago and so far it is a happy amp .
Yes there is a little fizz and ticking in the very background with no input, and the transformer has the typical Radford STA15 hum, but not nearly as loud as some I've heard.
Not bad for a valve amplifier that's likely 56 years old and still original apart from 2 valves.













Okay some of the voltages are awry, but that is leaky electrolytic caps, especially C2 on one side with only 30 volts on the screen...

So strip her down next and see what she needs.
Looks like I will be talking to Will at Radford Revival soon.
Alan
 
Cool, the fact it works suggests all transformers are ok, the rest can be dealt with! Are you going for a full-on restoration or keeping the shabby chic aesthetic?

PS My first TL12 Plus, the one from the local auction, came with a leaked late ‘50s Mullard GZ34 ‘fat-base’. So annoying as all the other valves tested ‘good’!
 
Graeme at Ampregen serviced mine after 20+ years without use, and for a very good price indeed. He reformed all the 64/65 electrolytics bar one which was beyond repair, so mine still has them too! He is very much in the ‘I don’t think it needs replacing, although I will with pleasure if you would like me to’ mould. The only other parts that needed to be changed were one resistor, one of the EL34s (cracked) and a lot of brittle wires on the valve bases. It also has a dicky phase splitter socket - once in a blue moon I lose the right channel. A light wiggle of the top of the valve brings it back immediately. All part of the charm! The (probably original) Mullard GZ34 failed about a year after that, but I replaced it with a vintage Bentley (Mullard date-coded 1965.) That’s been fine for two years now.
 
Looks like a great find Alan! Another classic saved from further decay :) And very brave to power it up and test, but important to have a starting point and know that the transformers are good before pouring many hours and $$$ into it. Having just finished my STA15 restoration off I dare say if I had the time I would dive right into another one, it was a lot of fun to do and I really like the way these amps are constructed. Will be keen to see how you get on.
Jonathan
 
Wow, what a find...looks fabulous.

I've been looking for a Radford to try and restore, having never worked with valves just SS previously.
 
For that rusty cage, I found a great company here locally (I am in South Africa) called Derustit. These guys dip your metal item into a (probably nasty) chemical bath which removes all coatings and rust, and item comes out basically ready for painting or powder coating. I'm sure you'll have a similar service somewhere close. A huge labour saving!
 
Quick update.
All stripped down...









Chassis and top cover will need a re-spray. Valve runners are too far gone, in fact they must have been rough from new, see the area round the left hand RCA socket. The handles will be okay, but the chrome trims are shot.
Only breakages so far are a lug off the one output transformer (there was one missing from the other and the wire soldered to the winding wire from new) and both the selector switch knobs fell apart...
Alan

More pictures here: https://photos.app.goo.gl/VpUCFZjwhYME1N6K8
 
snowman_al said:
Valve runners are too far gone, in fact they must have been rough from new, see the area round the left hand RCA socket.
Click to expand...

They don’t look too bad in the picture, I’d have thought some rust-removal treatment and re-plating them would bring them back. By saying that probably far easier just to replace them and the sockets if spares are available. The boards look nice and clean with no evidence of dodgy reworking. The transformer tags are the worrying bit to my mind, but I guess if there is something accessible to solder to it’s fine. Looks really promosing overall and I’m looking forward to seeing another vintage classic brought back properly!

PS I have to admit if it was mine I’d be in two minds how to restore it. I’d actually be half tempted to thoroughly clean and use a rust-stopper/remover, but leave the weathering/patina, kind of like a lovingly restored vintage Strat. I’d obviously go for a full-on electrical restoration, replace broken knobs, pots, connectors, tarnished valve bases etc and to the highest level possible, get it absolutely perfect from that perspective, but I do kind of like the barn-find/rat-rod aesthetic this particular amp has and suspect it could look cool if it was cleaned up in an ‘archival’ manner!
 
snowman_al said:
Quick update.
All stripped down...









Chassis and top cover will need a re-spray. Valve runners are too far gone, in fact they must have been rough from new, see the area round the left hand RCA socket. The handles will be okay, but the chrome trims are shot.
Only breakages so far are a lug off the one output transformer (there was one missing from the other and the wire soldered to the winding wire from new) and both the selector switch knobs fell apart...
Alan

More pictures here: https://photos.app.goo.gl/VpUCFZjwhYME1N6K8
Click to expand...

I don't want to upset you. However those pcb's in your 3rd pic down make me shudder.

I know, from my own Radford upgrades, that improving or bypassing the original Radford pcbs bring a clear, good upgrade. This can be done by either:

1) lining the pcb tracks with a coating of high purity silver solder, or

2) cutting all the tracks and substituting high purity silver /ptfe insulated wire point to point, using silver solder.

The second method is preferable.

Either will bring good- or substantial - improvements, depending upon your system and ears.

Anyhone who has not tried these (and other mods) to the Radfords should not be listened to until they do.
 
eguth said:
I don't want to upset you. However those pcb's in your 3rd pic down make me shudder.

I know, from my own Radford upgrades, that improving or bypassing the original Radford pcbs bring a clear, good upgrade. This can be done by either:

1) lining the pcb tracks with a coating of high purity silver solder, or

2) cutting all the tracks and substituting high purity silver /ptfe insulated wire point to point, using silver solder.

The second method is preferable.

Either will bring good- or substantial - improvements, depending upon your system and ears.

Anyhone who has not tried these (and other mods) to the Radfords should not be listened to until they do.
Click to expand...

Total bollox!
 
Raoul Duke said:
For that rusty cage, I found a great company here locally (I am in South Africa) called Derustit. These guys dip your metal item into a (probably nasty) chemical bath which removes all coatings and rust, and item comes out basically ready for painting or powder coating. I'm sure you'll have a similar service somewhere close. A huge labour saving!
Click to expand...

For my Leak 20 chassis, which was absolutely pitted with rust, a local sandblasting firm did in a couple of minutes what I couldn’t do in a couple of hours with an electric drill and wire brush.
 
russel said:
For my Leak 20 chassis, which was absolutely pitted with rust, a local sandblasting firm did in a couple of minutes what I couldn’t do in a couple of hours with an electric drill and wire brush.
Click to expand...

Blasting with a fine media is definitely an option, but the dipping option seemed safer to me at least for the much thinner and more delicate Radford cage.

Nice progress Alan, you wasted no time in getting started! Those transformer tags are so fragile, I lost one or two on my amp as well.
 
Thanks for the input everyone, lots of choices to make...

I've been making a list of parts I need, and going through the resistor values on the boards. Just a few out of spec.
A couple of questions for those who have done these before.

First each of the 390Ω cathode resistors is a different value, from 375 to 410Ω (?). Is the opinion to replace them with 390Ω again or swap them to 470Ω ?

And second regarding the red Wima coupling caps. They all measure fine and have no leakage at 300 volts, so should I replace them or leave them as is? Is there a better modern version for example?

I've given the boards a good clean and removed the 'green' from the tracks and re-soldered over them where needed.

Ta, Alan



 
I’d personally leave anything that is in spec and consistent across both channels (i.e. replace anything dodgy as L/R pairs). My aim would be to try and retain the original voicing as much as possible. It looks far more possible with these than with say Leaks which are full of carbon comp resistors and paper caps etc. It makes me want to buy one, but then I check the price of NOS Mullard EL34s and back quietly away!
 
The original Wimas should be fine. I tend to use 470R output cathode resistors but that isn't mandatory, you'd probably want closer matching resistors regardless of nominal value to what you have either way though!
 
snowman_al said:
Thanks for the input everyone, lots of choices to make...

I've been making a list of parts I need, and going through the resistor values on the boards. Just a few out of spec.
A couple of questions for those who have done these before.

First each of the 390Ω cathode resistors is a different value, from 375 to 410Ω (?). Is the opinion to replace them with 390Ω again or swap them to 470Ω ?

And second regarding the red Wima coupling caps. They all measure fine and have no leakage at 300 volts, so should I replace them or leave them as is? Is there a better modern version for example?

I've given the boards a good clean and removed the 'green' from the tracks and re-soldered over them where needed.

Ta, Alan



Click to expand...

I can't see any point in replacing the Wimas either but I have these available if it helps.
 
I have tried all types of Russian ex mil caps(p.i.o/silver mica/teflon)as well as other boutique types and went back to the original Wima's.I would recommend changing the original dual section 'lytics to F&T dual section ones which are very good,and they look better than 2 caps twisted together i.m.o
 
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