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Quad ESL57 frustrations. - Page 4

post #46 of 60

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.

post #47 of 60
Thread Starter 

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.

post #48 of 60

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
post #49 of 60
Thread Starter 

I bet not to many people have seen the inside of one of these. I only opened it because one rca connector was loose but I managed to tighten it up.

post #50 of 60
Small OTL amps work great with Quads. I used to use old Futterman amps with mine. I wonder what a push pull 300B amp would sound like with Quads?
post #51 of 60

It really depends on the actual amp topology rather than the tubes used.  A good p-p design could work well and deliver enough voltage swing to make the ESL happy

post #52 of 60

Keep in mind that the 57 is a highly reactive load.  It will cripple some amplifiers that can't handle anything but a fairly resistive load.  The Bedini 25/25 is a perfect match, but I'm not sure about the 10/10s.  I guess you've done your homework, correct? 

post #53 of 60
Thread Starter 

I have a few amps in the collection now. Some I won't get to try till next summer though. Radford Sta 25 is my favorite so far but also have Pioneer M22 , Quad 2 system and the Bedini. Trying other speakers too. Tannoy gold 12's and Spendor S3/5se I have not seen yet. Do I need more power for the Spendor's?

post #54 of 60
Originally Posted by jaycalgary View Post

I have a few amps in the collection now. Some I won't get to try till next summer though. Radford Sta 25 is my favorite so far but also have Pioneer M22 , Quad 2 system and the Bedini. Trying other speakers too. Tannoy gold 12's and Spendor S3/5se I have not seen yet. Do I need more power for the Spendor's?

I haven't seen the electrical load and phase curves for that amp.  I have enjoyed my Stirling LS3/5As with as little as 9W and they sounded great, but they never go below about 8 Ohms.  Of course, some people won't play an LS3/5A with less than 100W.  They all sound good on current amps, too (understanding that "all" includes the spin offs of the LS3/5A, as well)..

post #55 of 60

I have been using 57s for decades. I've been through many amps including Futterman H3aa, and NYAL OTL 3, but the best match by far has been the Audio Note P2-SE, which breathes life into the speaker like nothing else I've tried.


In general I have found that tetrode and pentode tube amps work better than triodes. Something like a 300b amp sounds tempting, but in my experience it doesn't work, sounding dull and lifeless. I've tried a bunch of them.

post #56 of 60
Thread Starter 

Anybody know dutch to have this ad taken down? This is a scam and I own amp presently and is in my possession. http://www.marktplaats.nl/a/audio-tv-en-foto/buizenversterkers/m833188822-radford-sta25.html?c=efb2ef4dc323389c4f92ed10afa33e3a&previousPage=lr   Power transformer hums a little bit on this one and the bias will go out of whack and make one of the el34s go cherry red. Have not used it since last summer as I have another one that works great. . Trying to figure out what the difference is between ef86 tubes and ef88 tubes. The amp has Russian ef88 tubes where ef86's should be. Going to get the proper ef86 tubes regardless. I don't speak Dutch and can't use translate enough to contact the site so somebody doesn't get scammed.

post #57 of 60

Seller says, original pictures will follow.... So I presume he has taken your pictures to illustrate his add!

post #58 of 60

Most people in the Netherlands can speak and read in perfect English. I would simply send an Email in English.

post #59 of 60
Thread Starter 

10 days now and he still hasn't put up his own pictures. I hope it is not a scam. I cant translate enough to make an account to email the guy.

Edited by jaycalgary - 8/12/14 at 6:49pm
post #60 of 60
Thread Starter 

Here is some of my Radford amps. It is the one on the top right.

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