Radford STA15 with Big Tannoys

[CliveG]

I thought I would share my experience in finding the ideal amp to drive my Tannoys.
I have been trying for a couple of years to find the perfect amp for Tannoy 15” Monitor Reds. I used to own AN/Es paired with my Shindo D’yquems and the sound lived up to both the reputation of Shindo and the liquid musicality you would expect from a 300B SET design.
I then came across a pair of original condition Tannoy GRF Corner Horns. They were fitted with 15” MGs and whist they sounded ok with the D’yquems something was missing in terms of dynamics and speed. I had the drivers re-coned and then external cross-overs built by Paul Coupe at RFC which improved the sound a lot but still something was missing, so I bit the bullet and bought a pair of Monitor Reds, which being 15 ohm would be an easier load for the amps. Again, even with new external cross-overs from RFC the sound was not quite there, so reluctantly I decided that no matter how much I loved the Shindos, I had to find a replacement better suited to the big Tannoys.
I have tried more powerful SE designs with KT88s and the PP EAR861 but still felt I was not getting the combination of musicality and dynamics that I was looking for.
Paul at RFC, who probably knows more about Tannoys than anybody recommended I try a Radford amp. I also followed Tom (Montesquieu)’s posts on here about his use of Radford with his Tannoys.
So when an unmolested STA15 in good condition became available I took the plunge. I had never heard a Radford before and had my doubts about 15w being adequate.
It was obvious as soon as it was turned on that I was on to something. There was a clarity and foot tapping pace to the music that had been missing, together with a musical mid range, sweet highs and plenty of controlled bass. There were some obvious issues due to the amp being in original condition but already new rectifier and input valves have resolved most of them. A quad of NOS Mullard EL34 resolved the rest and sound-wise there is nothing else required.
I know it will need to go off for a full service and probable replacement of some internal components but I have heard enough to know that the STA15 is a great match for the Monitor Reds and has more than enough power for the job. That such a small amplifier can sound so good after over 50 years is a testament to the design and manufacturing skills of its maker.

[Macca]

I remember hearing a Radford STA15 after a long day of many good amplifiers. And it was just right - to the point where I realised all the others, good as they were, were slightly wrong.


Exceptional bit of kit, congratulations.

[montesquieu]

No surprise that even an expensive 300b amp was unable to control the big cones - all these big Tannoys (Golds, Reds, HPDs) need a decent damping factor, something you will never get from a 300b SET.

I settled on Radford after experimenting with more than 40 amps across 12in and 15in Golds and HPDs. The Reds won't need many watts but they do need the control the Radford provides. Surprised you didn't like the EAR 861 but perhaps with Reds it was simply overkill!

There is something magical about the Radford amps with Tannoys, it's just a super combination. As you have discovered :)

Nice one!

(BTW the STA15 still gives out about 28 watts per channel, the STA25 with the solid state rectifer about 36 watts ... people sometimes get confused by the name and compact size but it's not a weedy thing at all!).

[cooky]

A few days ago I had Marchbanks from PFM over to mine to audition some 15" HPD Amesburys that I'd just finished fully restoring.
He brought along his STA15. The combo produced pure magic, more than enough power and the Amesburys sang a sweet musical song with great articulate bass, liquid mids, astonishing ambience and sweet sweet top. A match made in heaven.
Frank

[CliveG]

The 861 is a lovely amp and with the Tannoys, is better than the Shindos in terms of control, but not musicality. The STA15 has even better control than the 861 and is to my ears more musical. Its something to do with timing and clarity, you want to tap your feet more with the Radford.

[Edward]

I came to this perfect match the other way around. I had Radford STA25s for years driving a variety of speakers (Harbeth, Radford, PMCS etc) and was always delighted. Then experienced Adam's Tannoys and was floored. More so when I took the Radford over to drive his Tannoys.

So when some Eatons came up with Tom I was round there pdq and grabbed them. Not one once of regret.

Now still mulling over getting bigger Tannoys for all the good reasons.

Mind you I'm currently using a Sugden Masterclass amp driving the Eatons, that works very well also.

E

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[CliveG]

I suppose its not surprising they match so well, since these amps were produced in the mid sixties and were expensive for the time, so were mainly used by professionals or serious audiophiles, with whom 15" Monitor Reds were very popular.
But what I find amazing is how the STA15 has more than enough power for these speakers, even taking into account Tom's point above about the real power output of these amps. I am having to use -20dB attenuators on the amp's inputs to get the pre-amp volume control to work over a sensible range.

[montesquieu]

I suppose its not surprising they match so well, since these amps were produced in the mid sixties and were expensive for the time, so were mainly used by professionals or serious audiophiles, with whom 15" Monitor Reds were very popular.
But what I find amazing is how the STA15 has more than enough power for these speakers, even taking into account Tom's point above about the real power output of these amps. I am having to use -20dB attenuators on the amp's inputs to get the pre-amp volume control to work over a sensible range.

That's not a power question that's input sensitivity .. Will built some attenuation into the inputs of mine so that it could be used with a normal high-gain preamp. Doesn't affect the power rating ... you don't lose any power by running attenuators, you just have more control over the input signal and the resulting output volume. A higher gain input signal just means you reach maximum output (and distortion) faster.

[CliveG]

That's not a power question that's input sensitivity .

Point taken Tom. In my view its a pity more amps do not have variable input attenuators to solve this problem, like the EAR 861 and Shindos. Makes life a lot easier.

[AD Audio]

A Radford STA25 I've just serviced and upgraded sounds great with my Tannoys as does a Radford TT100 I've more or less completely restored so there's two that work well! I more or less wrote off the Radford STA 25 as a combination with my Tannoys before its service and upgrades but now it's really sounding great, so just shows what a difference running correctly and sympathetic upgrades can make!

The Radford TT100 of course has a lot of extra power but as Clive says about the 15, the smaller Radfords can certainly pull weight and on my 96db sensitive Canterburys certainly go loud enough for decent volume levels
David

[CliveG]

Its now with David at AD Audio for a service and some updating, such as new valve runners, speaker cable sockets and some input attenuation. Even in its present state I miss it already and looking forward to its return all singing and all dancing.

[AD Audio]

I tried it before any servicing or updating with my big Tannoy Canterburys and it sounds pretty decent! Amazing that a 50 year old amp is still going strong. It seems to have had one service and main power supply cp replaced at around 30 years ago otherwise it looks like it's original and untouched. It'll be ready for another 50 years' service after the servicing and upgrades we're doing!
David

[AD Audio]

Here's a few photos of the finished amp. The chrome valve runners from Will at Radford Revival really complete the upgrades to the amp and come with new valve and input sockets.

The work done to the amp was the following:
-replace all electrolytic capacitors
-change cathode bypass capacitors to Elna Cerafine
-swap coupling capacitors for Mundorf ZNs
-change speaker binding posts for Audio Note silver plated
-add 20db attenuation to the input

The goal was to replace worn components and use some better-performing modern equivalents in key places while retaining the voicing of the original design. The penultimate photo below shows the new chrome valve runners alongside the original electrolytics dated 1964 and 1965.

I soak tested the amp for two days in my workshop using a variety of music and as a friend who popped round remarked the amp is 'stupidly good' and sounds just so musical with everything from Bach choral works to jazz from France Musique.

I'm sure Clive will be along shortly with his impressions!
David
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[walpurgis]

Lovely. I'd like one like that if I could afford it.

[CliveG]

David has done a fantastic job, essentially keeping the sound character whilst solidifying the bottom end. Great workmanship and a nice bloke to deal with.
I played it for several hours yesterday into the Monitor Reds and today have switched over to the Golds. It sounds great with both but also highlights the differences between them far more than I have heard before. To my mind its impossible to say which is best, you just have to choose which feature of the sound presentation is more important to you.
Thanks David, I now have a long term solution to driving my Tannoys.

[Mostec]

Hello to all,

I’m looking to buy this Radford STA 25 Mk IV. My preamp is Croft Super Micro from year 1986, speakers are Tannoy Edinburgh HE and Autograph Mini. I don’t have a chance for demo listening to Radford.
What do you think will this be good combination? Room is 45m2, I mostly listen to jazz and vocals. Please take a quick look at Radford, is it in original condition, no modifications?
Thank you very much in advance for your help.
Have a good day.
Kindly Regards,
Primoz Draksler from Ljubljana - S[emoji172]nia
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[AD Audio]

I think the Radford will be great unless you like metal at stadium volume!
David

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[Barry]

Here's a few photos of the finished amp. The chrome valve runners from Will at Radford Revival really complete the upgrades to the amp and come with new valve and input sockets.

The work done to the amp was the following:
-replace all electrolytic capacitors
-change cathode bypass capacitors to Elna Cerafine
-swap coupling capacitors for Mundorf ZNs
-change speaker binding posts for Audio Note silver plated
-add 20db attenuation to the input

The goal was to replace worn components and use some better-performing modern equivalents in key places while retaining the voicing of the original design. The penultimate photo below shows the new chrome valve runners alongside the original electrolytics dated 1964 and 1965.

I soak tested the amp for two days in my workshop using a variety of music and as a friend who popped round remarked the amp is 'stupidly good' and sounds just so musical with everything from Bach choral works to jazz from France Musique.

I'm sure Clive will be along shortly with his impressions!
David
https://uploads.tapatalk-cdn.com/20180809/5fa846ded31e31470ae4731796776106.jpghttps://uploads.tapatalk-cdn.com/20180809/d5796ef7e874ba14eb66f1457e343888.jpghttps://uploads.tapatalk-cdn.com/20180809/b89ea24317e9ca0bbb2cbfbbe415c420.jpghttps://uploads.tapatalk-cdn.com/20180809/c3aebf10d5b46ddb6e17d081f5e29e54.jpghttps://uploads.tapatalk-cdn.com/20180809/a2ff08baeca4bb4578846628423e64a2.jpg

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Wow! Lovely work. Wish my STA15/III looked as good as that.