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Radford STA25 Mk III -- a lot of questions.

If bought from emporium it isnt a private sale, its from a retailer, the consumer (buyer) has certain rights.
I imaging the shop will sort the problem out if you talk reasonably to them.
I also imagine that if you get all uppitty and start threatening all sorts they may well call your bluff,and who could blame them
 
The one item I have bought from Emporium was as described, well packaged, and has given no problems.

However... the vendor is operating in a limited, probably shrinking market in which many potential buyers are members of forums like this one.

Potential buyers' perceptions of fairness are likely to be critical to the survival of a business in such a scenario.
 
It may be that when two caps have apparently been used in series to get the voltage rating required it has been done without taking precautions to make sure they share the voltage fairly equally.
How do you do that Jez? Would you set up a voltage divider with high value resistors so that the voltage equalised? Would the resultant current bleed through the VD be tolerated? I suppose that it would for smoothing caps, it's not going on through anything else.
 
It's one of the reasons I got out of the vintage scene many many years ago. People buy 50-60 year old amps and then expect them to work perfectly for further years without any servicing or overhauling. All vintage amps need completely rebuilding and all the components replaced, possibly the wiring replaced too. Certainly, that will be the case for any old Radford. That way a company selling such items can at least guarantee the product for 3, 6 or 12 months etc. Problem is, no one wants to pay the price for this service... If you buy any vintage/classic amplifier you should budget at least as much again for a proper overhaul. That way it should last (if done properly) another 40 years without any issues...
Owning a vintage/classic amp is a lot like owning a vintage or classic car. It's more of a hobbyist thing and it helps if you know how to maintain it yourself...
 
How do you do that Jez? Would you set up a voltage divider with high value resistors so that the voltage equalised? Would the resultant current bleed through the VD be tolerated? I suppose that it would for smoothing caps, it's not going on through anything else.

Yes to all Steve
 
As a Radford STA25/111 user for many many years, they are as reliable as any if used regularly and if the bias voltage setting is monitored regularly at 2 volts, they just play happily for ever.

I bought one for my brother in law c/w an SC22P and a FMT3, he never monitored the bias voltages and had the same capacitor blow up, sounds like the failure as yours.

Without using good quality EL34s, expect bias voltage fluctuations and capacitor failures.

I use Mullard EL34s, never any troubles.

You can also use GEC KT77s as an alternative choice, nice valves, especially Gold Lions.
 
Yes to all Steve
Bloody hell, good to know that I haven't forgotten everything I learned. So you select resistors to give say a few tens of mA through the VD and let physics sort the rest.

As regards this Radford, I have a Yaqin MC 10, with 2x EL34 a channel, is it a shared or similar circuit? Sounds very good, either way.
 
Right, I've just spoken to Nicholas Besley at Emporium, he wants to have a go at repairing the amp and I've decided to give him the chance. He says he has staff who can do it.
 
Right, I've just spoken to Nicholas Besley at Emporium, he wants to have a go at repairing the amp and I've decided to give him the chance. He says he has staff who can do it.

I've heard that before. I had an amp that was a simple repair, it went back and forth to Emporium until I gave up. Should have trusted my instincts and asked for a refund to begin with, or had someone I who I could vouch for their skills and experience look at it first.
 
If you post or PM me a picture of the amp with the bottom cover removed and the top cover removed (a pic from below and one from above) I can probably diagnose the issue by sight alone if it's obvious what has smoked up. Might be a good idea before the amp goes anywhere!
 
If you post or PM me a picture of the amp with the bottom cover removed and the top cover removed (a pic from below and one from above) I can probably diagnose the issue by sight alone if it's obvious what has smoked up. Might be a good idea before the amp goes anywhere!


Excellent idea, might be worth asking the supplier if he minds you taking off the bottom cover and looking inside.
 
transformers are very expensive, capacitors can be but theres little point, resistors are not
 
Bloody hell, good to know that I haven't forgotten everything I learned. So you select resistors to give say a few tens of mA through the VD and let physics sort the rest.

As regards this Radford, I have a Yaqin MC 10, with 2x EL34 a channel, is it a shared or similar circuit? Sounds very good, either way.

You need the current through the VD to be sufficient to swamp leakage currents of the caps.

The Yaqin is not the same circuit no. The Radford is considerably more sophisticated....
Yaqin is more similar to Leak St20.
 
If you post or PM me a picture of the amp with the bottom cover removed and the top cover removed (a pic from below and one from above) I can probably diagnose the issue by sight alone if it's obvious what has smoked up. Might be a good idea before the amp goes anywhere!

As the STA 25 ran for 6 hours, that to me says bias capacitor failure, a simple diagnostic and repair job.

If the PSU reservoir capacitor/s failed, that would have taken minutes to fail, and possibly take out the mains transformer.

The mains fuse should have blown before a catastrophe!
 
As the STA 25 ran for 6 hours, that to me says bias capacitor failure, a simple diagnostic and repair job.

If the PSU reservoir capacitor/s failed, that would have taken minutes to fail, and possibly take out the mains transformer.

The mains fuse should have blown before a catastrophe!

Very unlikely indeed! PSU reservoir caps most likely. If the OP posts the pictures here I will have a look also...
 
Very unlikely indeed! PSU reservoir caps most likely. If the OP posts the pictures here I will have a look also...

My wager is on bias capacitor fail.

;)

PS: Unless the mains reservoir capacitors had been replaced and not properly being reformed after a standing long shelf life.
 


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