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The Grand Wazoo
21-07-2009, 21:29
This is the text of an advert taken out by Radford in HFN in 1969


About Power Amplifiers – Valve or Transistor?

If you are about to purchase a high quality amplifier, the question – Valve or Transistor type? – is bound to arise. There are too many parameters to equate and too much conflicting hearsay to make the answer clear cut.
However difficult the purchasing problems may appear to the discriminating buyer, the problem facing the manufacturer of valve amplifiers, jealous of his reputation in respect of performance and reliability, is even greater.
Let’s face it. Generally speaking transistor power amplifiers have not turned out to be quite what we were led to believe. We have found all manner of faults and snags in practice which were not envisaged. Omitting such objectionable characteristics as blowing up when the output is short circuited, what is basically wrong? In the main, transistor amplifiers sound different from valve amplifiers, and produce listening fatigue. This we believe to be due to some design inaccuracies, but fundamentally to the use of the high power-efficiency class ‘B’quasi-complimentary circuit.
This circuit inevitably produces a large amount of distortion by class ‘A-B’ valve standards. The reasons for this will be given in an article to be published later. Simple harmonic slope distortion can be reduced by negative feedback but the effects of crossover distortion cannot. Have you noticed that in most transistor amplifiers the measured harmonic distortion does not decrease linearly with output? The most significant observation is, however, that the amplifiers sound far worse than measurements indicate when compared with valve amplifiers.
Good transistor amplifiers can be made, of course, but the disparity in price to performance ratio when compared with valve amplifiers has been too great to ignore except for professional users.

How does the best transistor amplifier compare with the best valve amplifier? It is not remarkable that one cannot detect the slightest difference in ‘A-B’ testing, or in the fatigue factor, on the finest reproducers available, on any kind of programme material. In our long but interesting research into transistor amplifier design it has been our endeavour to build an amplifier that sounds the same as a ‘Series 3’ valve amplifier.

What is the message? It is, that if you have purchased, or are about to purchase, a good valve amplifier, it will not become obsolescent in respect of performance. If you purchase a transistor amplifier it will be for other reasons.

Radford Audio Limited
Ashton Vale Road
Bristol 3


Discuss................
(I'd be interested to hear your thoughts, but only if you feel like it)

http://img32.imageshack.us/img32/2492/sta15.png
Front cover of manual from SC2 & STA15 pre/power amps.

SPS
21-07-2009, 22:25
I owned an identical sta15.. i was very suprised with its performance i was using a singe ended px4 diy amp at the time, the radford was very close to to it..

i sold it about 71/2 years ago when i got divorced.. i dont really regret selling it, but it was the best 'bought' amp i've owned... had I not been making amps i would still be using it..

triode connected mullard el34's.. into very good transformers nice,

steve

The Grand Wazoo
21-07-2009, 22:44
I owned an identical sta15.. i was very suprised with its performance i was using a singe ended px4 diy amp at the time, the radford was very close to to it..

I have an STA15 which is cosmetically extremely ratty, but sounds fantastic. It caused me to entirely reassess my take on hi-fi gear & I will never sell it.
Two of the best systems I've ever heard were driven by STA15's &, unbelievably, not so long ago they were almost being given away. It will happily be used with some very exotic kit indeed & stands as a testament to Arthur Radford's mastery of the art. Some technology is very slow moving - despite what some will have us believe!


The thing that interests me about the above article is that so much of what it says is still true today. OK, so solid state technology was still in it's infancy & lots of lessons have been learnt since then, but even so, it seems extremely prescient to me - slow moving technology indeed!

Cheers

scip
31-07-2009, 17:26
I am very lucky to know this classic amp from Chris and lucky enough found a sta15 in really good condition. All original Mullard valves, besides one CVC faulty gz34 rectifier valve. Just today, I replaced the GZ34 by one double ring big base Mullard GZ34(second hand,cost 80GBP), guess what!? much more clarity, enough bass, touching vocal! I never expect ls3/5a can sing like this, and I never heard this kind of sound before! Refer to rectifier valve, I know pp amp less sensitive to this than se amp, but sta15 really sensitive to rectifier tube.

Another incredible thing is high quality, all insert components in my sta15 are original and all tested in good working condition! I have a series 3 amplifier user manual come with the amp, follow that, the transformer life expectancy of 21years continuous duty, what a quality, my macbook air only claim one year warranty, then I have to buy apple care to insure the quality, oops, technology! I like vintage! like marantz quad radford, these company only care how to make product perfect, they don't have cost control, you can use them life time long, that's why all these company bankrupted!

Maybe I will go to find a pair of Quad ESL57 speakers instead current LS3/5A.

Today, when we look back to this article, looks like Radford know better than others, at the same time lots valve amp producer change their work to transistor amp.

Sorry for my poor english and long post.

Best regards,
Mawen

The Grand Wazoo
31-07-2009, 17:43
Hi Mawen,
That Mullard rectifier has gone up in price alarmingly over the last few years. I bought some at a very cheap price a while back & I'm glad I did so when I had the chance - so I probably have enough spares to last me out!

Radford did actually end up producing transistor amps eventually, though!

It's great that the Radford's working out well for you, Mawen - I thought you'd like that combination!

Cheers

scip
31-07-2009, 18:48
Hi Chris,

Compare to ls3/5a, do you think esl57 is a better choice for radford?

Best regards,
Mawen

The Grand Wazoo
31-07-2009, 19:03
LS3/5a or Quad?

Good question!
Can't answer it for you though, I'm afraid!

If you can place a good set of Quads in your room in such a way that they're capable of doing what Quads do best, then I'm sure they'd sound fantastic. But you have to bear in mind they're 2 very different speakers, designed to do different things in different environments. Many people aren't able to release the potential of their Quads because their room &/or lifestyle doesn't allow for ideal placement, but they buy them and keep them because of their reputation - a terrible waste of a good set of speakers I think!

I don't know anything about your taste in music or it's presentation, or your room so I couldn't comment. You'd have to try these things for yourself, I think.

Sorry.

scip
31-07-2009, 19:31
Thank you Chris, I will get them together and let you know the result.

Best regards,
Mawen

spendorman
26-09-2009, 09:39
Radford STA25 III /SC22/ FMT2 has been here 35 years + and I was not the first owner. I still amazes me with its sound quality, and its incredible reliability.

Nothing has needed changing. I have only changed output valves as I wanted to try KT77's. The original Mullard EL34's are still fine.

My friend has just purchased an STA20 and SC22, yes STA20, not 15 or 25. A very rare amplifier. I wonder if anyone has info on this model.

It looks like an STA15 III chassis, but where the GZ34 would normally be there is a plug in solid state rectifier bridge in an octal plug.

Here are pics of the STA20.

The Grand Wazoo
26-09-2009, 16:51
Interesting - I've never heard of such a thing. I've just been doing a bit of research on the brand & never came across any references to it.

You have a PM

spendorman
26-09-2009, 17:36
A little info on the STA20 and others.

DSJR
26-09-2009, 19:19
Just finding this thread, despite its age, the article first posted should be regarded as absolutely true FOR 1969!!!!!!!!!! Things have massively changed in the world of transistors in the last 40 years...

I LOVED the STA25 I had. Another valve amp that doesn't particularly sound "valvey." When it came out, it really was a huge step forward in the world of amplification I understand. Mine was around eleven years old when I bought it and the supply caps were leaking (have you checked yours underneath?). I suspect the preamp would be rather lacking today though - a Croft at £350 eating it alive I suspect...

spendorman
26-09-2009, 19:49
Its about 18 months since I last looked under the chassis of the STA25, just looked now, seems OK

scip
20-11-2009, 16:11
Hi CHRIS,

I got a pair esl57 today, they sounds amazing with radford sta15, I think I would like keep them for a life time.

Best regards,
Mawen

Rare Bird
20-11-2009, 16:18
Superb

spendorman
20-11-2009, 16:33
Hi CHRIS,

I got a pair esl57 today, they sounds amazing with radford sta15, I think I would like keep them for a life time.

Best regards,
Mawen

Wonderful, look after them.

How does the STA15 work with the LS3/5a? My STA25 III is wonderful with Chartwell 15 Ohm LS3/5a

scip
20-11-2009, 16:41
sta15+ls3/5a They works fine, but I finally sold my ls3/5a, esl sound more natural and open to me.

spendorman
20-11-2009, 16:49
sta15+ls3/5a They works fine, but I finally sold my ls3/5a, esl sound more natural and open to me.

Yeh! but much bigger!! I have two pairs of ESL57 as well.

Rare Bird
20-11-2009, 16:59
Yeh! but much bigger!! I have two pairs of ESL57 as well.

Stack em Paul, you'll have a wall of sound even Phil Spector would be proud of

:doh:

spendorman
20-11-2009, 17:01
Stack em Paul, you'll have a wall of sound ever Phil Spector would be proud of

:doh:

With the 63's as well?

The Grand Wazoo
20-11-2009, 21:35
Crikey, Scip, you don't hang about! It's great that you like the combination - it's pretty special, isn't it?

scip
21-11-2009, 06:08
Hi Chris,

Yes, and I think if you like sta15, esl57 worth to have a try.

Best regards,
Mawen

Barry
21-11-2009, 18:01
Hi CHRIS,

I got a pair esl57 today, they sounds amazing with radford sta15, I think I would like keep them for a life time.

Best regards,
Mawen

Nice find Mawen, they look to be in very good condition. Welcome to the Quad ESL57 owner's club.

You will need to take care with their positioning; your's seem to be too close to the rear wall, and the glass door to the right may give you trouble. You might even have to have a narrow rug placed in front of each speaker to cope with the uncarpeted (and hence reflective) wood floor.

Anyway, good going - let us know how you get on with them.

Regards

scip
22-11-2009, 07:53
Thank you Barry,

Speakers total refurbished by one thing audio, I bought them from classique sounds Paul.

Thank you for the position tips, I will follow it.

Best regards,
Mawen

shahsy
10-01-2010, 13:33
I've just bought a Radford STA25 and it pairs up very nicely with my Yamaha NS1000M's.

It's being used with a World Designs Pre3/Phono3s and it's being used in place of an MF A5CR power amp.

Very happy with the sound.:)

Does anyone have any tube-rolling experience of these?

s

spendorman
10-01-2010, 13:43
I've just bought a Radford STA25 and it pairs up very nicely with my Yamaha NS1000M's.

It's being used with a World Designs Pre3/Phono3s and it's being used in place of an MF A5CR power amp.

Very happy with the sound.:)

Does anyone have any tube-rolling experience of these?

s


Tried GEC KT77's in my STA25 III replacing the Mullard EL34's. Very good, but difficult to tell if better, possibly. The GEC's are so rare bought some JJ KT77's, did not notice any difference between them and the GEC's, but a lot cheaper!!

shahsy
10-01-2010, 14:17
Funnily enough, I've got the JJ KT77's in right now!

There are some EF86's and ECF82's also in the amp, would changing either of these likely to change the much?

s

spendorman
10-01-2010, 14:47
Mine are Mullard EF86's and ECF82's came with the amps well over 30 years ago when I got it. I have tried NOS ones in, no difference to my ears. Don't know about other brand's though. My original Mullard EL34's are still OK as well. The amp, it's valves and spare valves will probably outlive me!

spendorman
10-01-2010, 14:50
Early STA25's can suffer from mains transformer mechanical buzz, there is a mod for this if it does this. Mod was fitted to later production as standard. My friends very rare STA20 suffered from buzz, the STA25 mod cured it.

scip
25-02-2010, 22:51
At first when I get my sta15, the transformer with louder noise. after changing gz34, it works fine.

Now I use a playstation scph-1002 as cd player, FURUTECH power cord, hifi tuning fuse, this plastic box sounds great in my system, clear and detail, then I sold my naim cd5i, will buy another ps1 for mod.

stephenred
14-04-2010, 03:43
I have far too much vintage hi-fi, including a Radford TT-100. This is Mr Arthur Radford's final statement in amp design, and is, interestingly, a hybrid. It has a solid state input stage and KT88 valves in the output. Massive transformers.

Old Arthur thought it offered the best of both worlds. I've never read any reviews on it, but it is amazingly ballsy and solid sounding.

It's been used by me on ESL 57s and 63s, NS1000Ms, 15 0hm Rogers LS3/5As, Spendor SP1s, 12" Tannoy HPDs and 15" Monitor Golds, and on the top end of a pair of actively bi-amped JBL 4344s. Good on most speakers, loves the Yammies and Tannoy HPDs for some reason.

The Grand Wazoo
14-04-2010, 10:55
I have far too much vintage hi-fi, including a Radford TT-100.
I'm sure I can help you out there - I'll provide accomodation for it at very competitive rates!

Arthur Radford knew his stuff that's for sure - his amps can still show plenty of modern gear a thing or two. Have you seen the history of the company in the AoS library?
That would be a great place for some photos of your TT100!

DSJR
14-04-2010, 17:27
I have far too much vintage hi-fi, including a Radford TT-100. This is Mr Arthur Radford's final statement in amp design, and is, interestingly, a hybrid. It has a solid state input stage and KT88 valves in the output. Massive transformers.

Old Arthur thought it offered the best of both worlds. I've never read any reviews on it, but it is amazingly ballsy and solid sounding.

It's been used by me on ESL 57s and 63s, NS1000Ms, 15 0hm Rogers LS3/5As, Spendor SP1s, 12" Tannoy HPDs and 15" Monitor Golds, and on the top end of a pair of actively bi-amped JBL 4344s. Good on most speakers, loves the Yammies and Tannoy HPDs for some reason.

Interesting that last sentence, as the yammies are rather over-damped in the bass, yet the HPD had the bass damping reduced compared to the Mon: Golds which preceded them IIRC.

Mr Radford sure did know a thing or two about his output transformer designs. I wonder if this is why tube-rolling doesn't make a huge difference here?

Ali Tait
14-04-2010, 18:39
Yes,it's often said that the iron's what makes these amps sound so good.I believe Mr Radford started out designing transformers?

DSJR
14-04-2010, 19:26
The STA25 series really did push the boundaries of valve amp performance in the early 60's I understand.

spendorman
14-04-2010, 19:35
Yes,it's often said that the iron's what makes these amps sound so good.I believe Mr Radford started out designing transformers?

Could be the reason Rogers used Radford transformers in their Master power amplifier.

http://www.gramophone.net/Issue/Page/December%201965/133/788950/Rogers+Master+Stereo+Amplifier.+Manufactured+by+Ro gers+Developments+%28Electronics%29+Ltd.,+414+Barm eston+Road,+Catford,+London,+S.E.6.+Price:+L50.

Ali Tait
14-04-2010, 19:49
there are some things in regard to valve amps that much more was known about in the past than is known now.

hifi_dave
14-04-2010, 20:54
Definitely and (to my mind) that also applies to turntables, speakers and certain cartridges...:doh:

Ali Tait
14-04-2010, 21:03
Yes,you've got a point there! Will who posts here,has a pair of 70-year-old field coil speakers on his OB's.They sound superb!

Barry
15-04-2010, 17:10
Could be the reason Rogers used Radford transformers in their Master power amplifier.

http://www.gramophone.net/Issue/Page/December%201965/133/788950/Rogers+Master+Stereo+Amplifier.+Manufactured+by+Ro gers+Developments+%28Electronics%29+Ltd.,+414+Barm eston+Road,+Catford,+London,+S.E.6.+Price:+L50.

Do you know this to be true? I can't find reference to it in the Gramophone link you provide, though it would not surprise me. I believe the secret to a good valve power amplifier does lay in the design of the output transformers. And yes, a lot of this sort of knowledge is being lost through lack of use. Most transformer manufacturers concentrate on power transformers; audio transformers, especially power transformers are a bit of a speciality

I've always been interested in this amplifier since reading about it in the late '60s. Does anybody out there have experience of one? (Andre? if your still reading AoS posts) It, along with the Radford 15 and 25 amps, the Lowther LL26 and Richardson MA135 or ST70, are all amplifiers using EL34s that I would love to get my hands on.

Regards

Ali Tait
15-04-2010, 18:25
Nick,who is building my direct-coupled amps,had a Radford in for repair,and was quite taken aback by it,saying it was almost good enough to make him give up his SE amps.If you know Nick,that's quite a statement!

The Grand Wazoo
15-04-2010, 19:19
As I said a while back on another thread, these amps (especially the STA & MA 15 & 25) tend to get lumped in with the Leaks & Quads of this world. This is a big mistake that would not be made by anyone who knows them!

The price of them at the time that they were current reflected this, and they more often than not ended up in professional applications simply because the enthusiasts just couldn't afford them.

Ali Tait
15-04-2010, 20:29
Yes indeed,they were regarded as the very best.

Jonboy
15-04-2010, 21:42
I think i have missed the boat on these as the prices are getting a bit steep for my pockets, i will have to wait until one comes along to borrow, hint hint ;)

Barry
15-04-2010, 21:55
I think i have missed the boat on these as the prices are getting a bit steep for my pockets, i will have to wait until one comes along to borrow, hint hint ;)

If anyone is in the queue to borrow a Radford amp, then I'm the first! ;)

Regards

hifi_dave
15-04-2010, 21:55
Radford prices have risen rapidly over the past few years. I sold an STA-15 and an STA-25, both immaculate, in the Autumn of 2006 and got approx £400 for each of them on E-Bay. Look how much they go for now !!!

Thank goodnes I still have my Radford mono's, pre and tuner....:lolsign:

Jonboy
15-04-2010, 21:59
Radford prices have risen rapidly over the past few years. I sold an STA-15 and an STA-25, both immaculate, in the Autumn of 2006 and got approx £400 for each of them on E-Bay. Look how much they go for now !!!

Thank goodnes I still have my Radford mono's, pre and tuner....:lolsign:

I'm first in your queue then Dave, my old friend and best buddy

hifi_dave
15-04-2010, 22:39
I think you'll have to climb over DSJR's body to be first in line.....:eyebrows:

Barry
15-04-2010, 22:56
I think you'll have to climb over DSJR's body to be first in line.....:eyebrows:

And then it's me! ;)

Regards

SPS
16-04-2010, 08:56
Radford prices have risen rapidly over the past few years. I sold an STA-15 and an STA-25, both immaculate, in the Autumn of 2006 and got approx £400 for each of them on E-Bay. Look how much they go for now !!!

Thank goodnes I still have my Radford mono's, pre and tuner....:lolsign:

thats a shame.. i sold an perfect boxed pre and power st15 mk3 and got £800 for it in 2002 .. it was a very good amp.. reading these posts i now feel a tinge of regret for selling it...

it was very good,... but as ali stated.... only almost as good as a very good single ended amp...

Ali Tait
16-04-2010, 09:33
Be nice to hear an SE amp with trannies of the same quality..

blstransformers
25-10-2011, 08:09
Hi Everyone,

I've just been searching on the internet for any information about Radford amplifiers. Someone has asked me to make him some power and output transformers for STA 15s and STA 25s. Does anyone know how large these transformers are? I've looked on Sowter's web shop and the designs they have for the outputs at least are massive. My initial calculations are showing DC resistances on the primary that are tiny and well below the 5-10% I work to when doing a "ground up" output transformer design.

If anyone's got any information at all, I'd be most grateful.

Simon

spendorman
15-01-2012, 21:19
Do you know this to be true? I can't find reference to it in the Gramophone link you provide, though it would not surprise me. I believe the secret to a good valve power amplifier does lay in the design of the output transformers. And yes, a lot of this sort of knowledge is being lost through lack of use. Most transformer manufacturers concentrate on power transformers; audio transformers, especially power transformers are a bit of a speciality

I've always been interested in this amplifier since reading about it in the late '60s. Does anybody out there have experience of one? (Andre? if your still reading AoS posts) It, along with the Radford 15 and 25 amps, the Lowther LL26 and Richardson MA135 or ST70, are all amplifiers using EL34s that I would love to get my hands on.

Regards

A little late!! lol, but proof here of the use of Radford transformers in the Rogers Master power amp:

http://farm5.staticflickr.com/4138/4783622260_a7d12ffd5c_b.jpg

electromuffin
08-09-2012, 22:28
Hi Alex an aquantence also has a ST20 but the lettering has rubbed off of the first valve in both channels. As your freind has one can your possibly help please
Best regards Len
PS He lives some distance away so I have not seen this amp and he is not that technical

The Grand Wazoo
08-09-2012, 22:44
Len,
Take a look in th AoS Library, where you will find an article about Radford. (http://theartofsound.net/forum/showthread.php?t=4168) There is a list of products with their valve complements itemised.