If the pictures you show are for a Radford-STA25-then somebody has totally stripped it down and done a complete rebuild. > No Hi-Fi amp from the 60s/70s is in that condition originally unless it was kept in sealed cupboard and hardly used. -Radford-STA-25=output-25W/RMS/channel-DIS.-0.1-FR-20HZ-60KHZ noise-90DB.Input 500MVfor stated output---OUTPUT IMPEDANCE=4/8/16 OHMS-Price[in1971] £60. What you have got is "most wanted" in the UK by valve[tube] addicts. It gets excellent write ups by the tube fraternity. I don't know how much you paid -maybe £600 or more [$850] but I wouldn't put it down according to people in the UK its better than a lot of well known names like Mullard[design] Sugden/Revox and many others. The price wont go down even if you don't like it there are plenty here who would buy it.- Information from the HI FI YEAR BOOK for 1971. I have a large number of them gives specs on speakers/amps/ decks/receivers early headphones etc.
Quad ESL57 frustrations. - Page 4
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It is a Radford STA25 I guess the pictures made it look a whole lot nicer the it does in person. It is quite a stinky old amp that certainly looks like it should have a fire extinguisher near by and never left on too long. That is my impression so far. I bought it because I knew that it was known to be great and was over $2k. Here is the listing http://www.ebay.com/itm/Radford-STA25-Series-3-Valve-Tube-Power-Amplifier-STA-25-/300907088738?nma=true&si=oeMESYLayuvEwGQywibht5vJi2Q%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557 The only thing I see odd is how the output transformer is wired because that is not the way they came. Maybe it was done to make it safer I don't know but I need to get a tech to look at it to make it safer. I just saw one that was burnt on ebay and I don't want that to happen to this one. I need to have jumpers moved on the mains transformer so it will work at 125v. The seller didn't think so but the manual says it needs it. Looks like it is now hard wired for an 8 ohms now. I thought I read the ESL 57s were best on 16 ohms but hopefully it will be okay. Can you see anything that I should be asking the Tech to do. I highly doubt he has worked on the model but everyone around here says good things about him.
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Sorry to hear about the condition it looks okay from the photos. If you google-information on the radford Sta25 tube amp you will get -Wikipedia and if you click on JLH article at the bottom you will see a circuit diagram of it . Yes the output impedance is switchable and you are right in my Hi Fi year book for 1973 for the quad els 57 the correct input impedance is -[as stated] -30 to 15 OHMS falling above 8KHZ meaning a drop at the "high end". The actual coverage is 45HZ to18KHZ. Using a "fixed" 8 OHM output would give an uneven frequency response from the Quads.If the 8 OHMS "sees" 8 OHMS[impedance at A CERTAIN frequency] that frequency will be amplified above the STANDARD frequency response at other frequencies [ because of output transformer matching]it will be reduced. Tube[using output transformers] and solid state aren't Exactly the same.Still looking for transformer connections.---Like to add the voltage connections are= 125V-140V-220V-235V-250V. You should be able to see the selector near the mains transformer. I was surprised to find that YAHOO has a "Radford Yahoo group" if you join you get access to all information on Radfords. In 1988 value of STA-25 was £1250-approx $1600 so You werent overcharged unless as you say it was in bad condition. And I got confirmation on other websites it is at least "one of the kings" of tube amplifiers and that just keeping it its value will increase.
Edited by duncan1 - 7/20/13 at 11:06am