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Radford STA25 Mk III -- a lot of questions.

Discussion in 'classic' started by mandryka, Aug 26, 2019.

  1. mandryka

    mandryka pfm Member

    I've been offered one of these (working) for what is, I think, a good price - a little under 1K. The dealer is Emporium, who has a decent reputation I think.

    Is that a reasonable price?

    What are the pitfalls -- the things I should look out for before taking the plunge?

    Do they hum badly? What are the costs of replacement valves?

    Who could restore it and is it likely to be an expensive restore? I assume that a restore will improve sound -- is that right? Is it the sort of amp which is known to benefit from changes?

    Will it drive Rogers JR 149s? Or Spendor SP 1s? I'm assuming it will not drive ESL63s, maybe I shouldn't make that assumption.

    I would use it with no preamp and digital volume control -- the DAC has 2V output. Will that work?
  2. Tony L

    Tony L Administrator

    Nice amp and a good price if in decent physical condition and not botched/modified/altered at all. These are classic and collectable amps and anything other than a sympathetic service/recap will always subtract value.

    Valve prices are hugely variable depending on whether you are happy with current production Russian or Chinese, or want to hunt down serious NOS. No correct answer to this, basically you can re-tube it for around £120 or well over £1k depending on what you want!

    I can drive my JR149s perfectly happily with a Leak Stereo 20, so the more powerful Radford would be in its element here. They will sound superb. SP1s shouldn’t be the slightest issue either. Not so sure about ESL 63s, but I’d have thought it would work fine though may have a volume ceiling. A pair of EL34s and nice output transformers goes a long way in practice, certainly further than the Watt rating would imply.

    IIRC the Radford is very high gain, the one I tried here was certainly happy enough with a passive pre, so driving from a variable DAC output should be fine.
  3. clive7164

    clive7164 pfm Member

    I have recently bought a series five ,its the best amp I have ever had.
    look here for full information

    Will at Radford is very helpful and also does fabulous work,there are a few threads
    with pics on AOS forum,a recent one showing one he has rebuilt restored for someone,
    He uses JJ tubes as standard which I dont think are dear and sound good in my amp.
    I drive Harbeth SHL 5 speakers with mine and they do that with ease.
  4. david ellwood

    david ellwood Kirabosi Kognoscente

    radfords have a number of tappings on the output transformer (4,8,16R) the higher impedance might suit quads?
  5. mandryka

    mandryka pfm Member

    Thanks for these positive sounding replies.
  6. eastone

    eastone pfm Member

    How does the Radford sound compared to previous amps you’ve used with the Harbeths. I am curious about what makes them such superlative beasts (the Radford amps)...
  7. TonyScarlett

    TonyScarlett pfm Member

    Like Tony L I have also happily driven my JR149s with an ST20 in my second system. Don't know much about Radford amps but when it comes to repairing/restoring vintage valve gear you should talk to Graeme at Ampregen in Didcot, he is a walking encyclopedia when it comes to vintage valve amps & a true gentleman. He did a superb job on my ST20 for a very reasonable price.
  8. mikeyb

    mikeyb pfm Member

    I nearly bought a valve amp from Emporium but I was warned off it by someone who knew the amp saying it had been, let's say, tampered with and wasn't going to sound how it was supposed to.

    Why don't you ask Radford about that one you're looking at as I'm sure they'll know all about it ;)
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Here's a rebuild I did a couple of years ago ish https://pinkfishmedia.net/forum/threads/radford-sta25-rebuild-pics.230695/

    £1k does sound a bit cheap for a "proper" one and especially from a dealer.

    The really important thing to be sure of is that the output transformers are good and are the originals! Mains transformer and smoothing choke obviously not easy to replace either but not as crucial as the outputs. Radford Revival can supply the transformers but don't expect them to be cheap!

    The phase splitter valve is a 6U8 and the real thing, NOS, is still easily available. NOS EF86 for first stage a bit more tricky but not as rare as say ECC83 and modern versions are available. The EL34 output valves are the trickiest to find good quality replacements for. I'd use Sovtek from those currently available.

    There can be a little bit of mechanical hum from the mains transformer but it's not enough to be a problem. There should be none at all from the speakers.

    it should drive pretty much anything you throw at it perfectly well.
  10. Radfordman

    Radfordman pfm Member

    I have owned an STA25 III for over 40 years. Never had anything wrong with it. My opinion is that audio quality is first rate, it has driven all speakers well, including ESL57's and ESL63's. If new valves are required, the JJ Range is very good, and good value too. I removed the original Mullard EL34's, which are still fine, to store, and I use either JJ EL34''s of JJ KT77's.

    The STA25 is more powerful than it appears, actually produces over 30 Watts RMS per channel.
  11. mandryka

    mandryka pfm Member


    The price is low because he's prepared to take a trade-in for some quad gear I don't need any more.

    How do I check this??!!
  12. mandryka

    mandryka pfm Member

    I've sent them an email through AoS. Thanks for the idea.
  13. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Detailed comparison with pictures of known real ones is about all you can do but it should be reasonably easy to ascertain its provenance from this.
  14. Replied via PM on AoS :)
    Darmok and mikeyb like this.
  15. I have looked at the pictures of said amp and they are the original output transformers
  16. mandryka

    mandryka pfm Member

    You are a star! Though now I’m not sure what to do. That’s to say, I’m not sure whether the modifications are important enough to mean that I should run away from the amp or not.
  17. mandryka

    mandryka pfm Member

    I’ve placed the order!

    One thing that’s puzzling me - what sort of input lead does it need? Some sort of DIN lead?
    Rosewind and eastone like this.
  18. Radfordman

    Radfordman pfm Member

    Excellent. I suspect that you are in for a treat.

    Normal phono (RCA) sockets on the STA25 III. Not DIN.
  19. eastone

    eastone pfm Member

    Exciting stuff! I’ll be dead keen to hear how it compares with your other kit.
    Rosewind likes this.
  20. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    ...yep! What a choice.. Krell KSA50 or Radford STA25... two of my favourite power amps of all time...
    Rosewind likes this.

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