The Radford Revival STA15 Review.

[stupinder]

As the Radford Revival STA15 is a reissue of an early 1960s design, we thought that the best way to give readers a full and clear picture of what this amplifier is capable of was to conduct two separate reviews.
In his first review of the Radford Revival reissue (http://hifipig.com/radford-sta15-series-3-re-issue-amplifier/), Paul reviews the amplifier as he would any other modern amplifier, with the caveat that some, but not all of the music chosen was contemporary with the design of the amplifier.
The second forthcoming review will compare and contrast an original STA15 against the Radford Revival STA15 Series 3 Re-Issue.
Special thanks must go to Steve and Will of Radford Revival who have kindly allowed us to be the first 'zine in the world to have a proper look and listen to this iconic amplifier!

[spendorman]

Very interesting, thank you, I eagerly await the second review.

My original STA25 III is wonderful. Just working out how long I've had it, probably approaching 40 years. Bought it second hand, nearly immaculate. Cost £150 with SCA22 pre and FMT2 MPX Tuner

Has proven utterly reliable. Even the original Mullard valves are still fine.


It's the one pictured here, you will have to scroll down:

http://www.adventuresinhifiaudio.com/03/07/2010/a-history-of-radford-electronics/

[stupinder]

Very interesting, thank you, I eagerly await the second review.

My original STA25 III is wonderful. Just working out how long I've had it, probably approaching 40 years. Bought it second hand, nearly immaculate. Cost £150 with SCA22 pre and FMT2 MPX Tuner

Has proven utterly reliable. Even the original Mullard valves are still fine.


It's the one pictured here, you will have to scroll down:

http://www.adventuresinhifiaudio.com/03/07/2010/a-history-of-radford-electronics/
Crikey!!! nice site by the way!!!

[Ali Tait]

I presume the comparison will be done with identical valves?

[stupinder]

I presume the comparison will be done with identical valves?
I will find out.

[Wakefield Turntables]

i cant wait for the comparison. I've not owned my Radfords for as long as some but there is no way that I'd get rid of them ;)

[Spectral Morn]

Crikey!!! nice site by the way!!!

Thank you.


Regards D S D L

[The Grand Wazoo]

Thanks for letting us see this Stu.
What I would find fascinating for a part three is a head to head with a modern EL34 amp of a similar price tag - I've always thought these amps are some of the least 'vintage' sounding of the big three UK makers of the time.
Although my STA15 looks like a bag of spanners, I'll never part with it.

[Reffc]

Worth noting guys that that SA15 is not an EL34 amp, it uses E34L valves which offer higher plate dissipation than EL34's for a smoother HF response. Just thought it worth a mention as this won't sound comparable to an EL34

[stupinder]

Valves same other than rectifier i'm informed.....
A third test would be interesting wouldn't it....

[Ali Tait]

Worth noting guys that that SA15 is not an EL34 amp, it uses E34L valves which offer higher plate dissipation than EL34's for a smoother HF response. Just thought it worth a mention as this won't sound comparable to an EL34

Can it use normal EL34's then? Otherwise a comparison with a vintage Radford is pretty meaningless..

[Reid Malenfant]

Sounds like it's biased higher Ali to give greater class A power if the different valves can sustain higher plate current :scratch: If so then maybe but possibly not for long :eyebrows:

[Ali Tait]

Yes, seems that way. Wondered if bias can be altered for normal EL34.

[Radford Revival]

Hi, I'd like to clear up a couple of things..

Our amplifiers use the original circuit with no modifications. In the case of the STA15, that of course includes the cathode resistors used for biasing the output valves. Historically you tended to find STA15s fitted with one of two values in this position - some had 390R, some had 470R. We actually use 470R resistors in ours, because we find 390R runs things a bit closer to the anode dissipation limit than we would like.

So despite the fact that we supply the amplifiers with E34Ls, which ARE EL34s but with an anode capable of a higher dissipation, they will work fine with "normal" EL34s. In fact they will have a slightly easier time than in most of the originals, which came with 390 ohm cathode resistors.

This has little to no effect on the measured performance, the harmonic spectra of the distortion is very favourable right up until the last 5% of the available voltage swing, when higher orders start to appear. This occurs on both ours and the originals.

[Reid Malenfant]

Ah, glad we have that cleared up, cheers Will :) So a really meaningful comparison could actually be done!

[stupinder]

The comparison review was only being done as the Radford Revival is such a close facsimile of the original circuit.
If it hadn't been then Hifi Pig certainly wouldn't have entertained the idea of a comparison - it would have been pointless.

[Ali Tait]

Hi, I'd like to clear up a couple of things..

Our amplifiers use the original circuit with no modifications. In the case of the STA15, that of course includes the cathode resistors used for biasing the output valves. Historically you tended to find STA15s fitted with one of two values in this position - some had 390R, some had 470R. We actually use 470R resistors in ours, because we find 390R runs things a bit closer to the anode dissipation limit than we would like.

So despite the fact that we supply the amplifiers with E34Ls, which ARE EL34s but with an anode capable of a higher dissipation, they will work fine with "normal" EL34s. In fact they will have a slightly easier time than in most of the originals, which came with 390 ohm cathode resistors.

This has little to no effect on the measured performance, the harmonic spectra of the distortion is very favourable right up until the last 5% of the available voltage swing, when higher orders start to appear. This occurs on both ours and the originals.

Good to know, will look forward to the review. The EL34L's may well be EL34's, but IMHO will probably sound different to standard/NOS 34's.

[Radford Revival]

Good to know, will look forward to the review. The EL34L's may well be EL34's, but IMHO will probably sound different to standard/NOS 34's.

Indeed, and luckily our amplifiers have no problem whatsoever with NOS valves :)

These aren't just rough impersonations of the originals - they have been made from the original blueprints (we actually have them!) and transformer specifications. The output transformers have identical interleaving of the windings, and every winding has exactly the same number of turns. The only difference between the original transformers and ours is that ours are made to a higher standard, with superior insulation materials, vacuum impregnation, better bobbins and much better tags on the transformers.

The metalwork is also identical to the originals, except for tasteful improvements we have made. For example, we use quality stainless steel for the transformer plates instead of zinc plated mild steel. We use bright stainless for the valve runners which looks very attractive, but isn't overly blingy.

[Reffc]

Further to Will's comments, and having the STA review sample sat in front of me, I can confirm what Will says. The Revival amp is almost identical with the exception that it's better quality! The recent review does mention this.

[Barry]

Worth noting guys that that SA15 is not an EL34 amp, it uses E34L valves which offer higher plate dissipation than EL34's for a smoother HF response. Just thought it worth a mention as this won't sound comparable to an EL34

No, not according to Radford`s own circuit diagram for the STA15, or the MA15. They use EL34 pentodes.

See the Radford reference material in the AoS Library.

Regards

[Reffc]

No, not according to Radford`s own circuit diagram for the STA15, or the MA15. They use EL34 pentodes.

See the Radford reference material in the AoS Library.

Regards

All I can tell you is that the STA15 sat in front of me now IS fitted with E34L's which as Will has explained have higher plate dissipation than normal EL34's. As Will has already pointed out, the amp can be fitted with normal EL34's too (as per the original), but I was referring to the review amp. Sorry for any confusion.

[Barry]

All I can tell you is that the STA15 sat in front of me now IS fitted with E34L's which as Will has explained have higher plate dissipation than normal EL34's. As Will has already pointed out, the amp can be fitted with normal EL34's too (as per the original), but I was referring to the review amp. Sorry for any confusion.

No need to apologise the confusion was mine!

Certainly a change of output valve might alter the sound, just as replacing the EL34 valves with KT77 valves will.

Regards

[Reffc]

Yes indeed Barry. I've always found KT77's to be a little punchier but lacking some of the appeal of the EL34's but guess its all very personal!