View Full Version : Just connected up an old friend, Radford STA25 III
spendorman
12-02-2017, 13:50
It's been so cold recently, thought that the extra couple of hundred watts or so of heat into the room would not be wasted.
Really enjoying the music, amp is connected to my slightly odd speakers, effectively, Rogers BBC LS3/6 fitted with Rogers Export Monitor bass units.
https://c1.staticflickr.com/1/614/32857794805_c7abae4fb5_z.jpg (https://flic.kr/p/S4wMDx)DSCF1239 (https://flic.kr/p/S4wMDx) by A60man (https://www.flickr.com/photos/41679262@N02/), on Flickr
https://c1.staticflickr.com/3/2076/32734114701_d442db1162_z.jpg (https://flic.kr/p/RSATRX)DSCF1241 (https://flic.kr/p/RSATRX) by A60man (https://www.flickr.com/photos/41679262@N02/), on Flickr
https://c1.staticflickr.com/3/2320/32857791875_ab925754a9_z.jpg (https://flic.kr/p/S4wLM2)DSCF1236 (https://flic.kr/p/S4wLM2) by A60man (https://www.flickr.com/photos/41679262@N02/), on Flickr
They are such an iconic amp. Would love to hear one.
dantheman91
12-02-2017, 14:32
Dribbling.........:drool::drool::drool::drool::dro ol::drool:
spendorman
12-02-2017, 14:41
I've had this amp for something like 40 years. It was not new then, made a sort of swap. Swapped my pair of 12" Tannoy Monitor Silvers in nice cabinets for the STA25. In hindsight, financially was not not a good deal at present day prices, however, I very much appreciate the amp, and have replaced the Silvers with HPD315's.
Very nice Alex.
Although I'm predominately a solid-state user (Quad, Mark Levinson), I wouldn't part with my Radford STA15 Mk. III. It's a lovely match with the Quad 57 ESLs.
(By the way, I corrected a typo in the title of your thread.)
spendorman
12-02-2017, 17:10
Very nice Alex.
Although I'm predominately a solid-state user (Quad, Mark Levinson), I wouldn't part with my Radford STA15 Mk. III. It's a lovely match with the Quad 57 ESLs.
(By the way, I corrected a typo in the title of your thread.)
Me too, usually, disconnected a Quad 303 to put the Radford on. There is a difference in sound. Prefer the Radford. My 57's may need some attention. I did some work on them about 27 years ago, new treble panels and various components on the underside of the audio transformers.
Thanks for correcting the typo, I'm quite good at those.
One day I'll have to A-B the Radford with a 303 using my Quads.
spendorman
12-02-2017, 17:20
One day I'll have to A-B the Radford with a 303 using my Quads.
Many years ago I tried that, to me the difference was not that much, with the other speakers the difference seemed greater. These Rogers speaker things are very revealing, in some respects, more so than the 57's.
The Black Adder
12-02-2017, 17:31
A proper amp... Lovely.
I have to be honest I think the aesthetics are in the "so ugly it's cool" camp. But ugly they are I'm sure to non hi-fi types.
spendorman
12-02-2017, 19:34
I have to be honest I think the aesthetics are in the "so ugly it's cool" camp. But ugly they are I'm sure to non hi-fi types.
I'm not too bothered about aesthetics, proof is that I have a Volvo 340!
The Black Adder
12-02-2017, 19:47
I love the look... you need 1960's industrial eyes to appreciate. :)
Arkless Electronics
12-02-2017, 20:13
I happen to have one in for service at the moment... Will add my subjective review when the work is completed... (I made a decision to not hear this legend until it's working A1). This will be the first time I've had the use of one in my own system.... known quantity.. known acoustics etc. I'm so hoping it won't be a let down to not just meet a hero but get to know him.. at least for a few days before it has to go back to it's lucky owner.
Should try an Sta -15,the Gz34 rec gives off more heat to keep your room warm:) and it sounds nice too.[had mine since 1981] Mick
Many years ago I tried that, to me the difference was not that much, with the other speakers the difference seemed greater. These Rogers speaker things are very revealing, in some respects, more so than the 57's.
I once compared the Rogers 'BBC Studio Monitors' (a spin-off of the LS3/6s; I believe we've had this discussion before) with the Quad 57s. Very close in sound quality, but I still prefer the Quads.
spendorman
12-02-2017, 21:05
Should try an Sta -15,the Gz34 rec gives off more heat to keep your room warm:) and it sounds nice too.[had mine since 1981] Mick
Strangely enough, all those years ago when I swapped Tannoy 12" Silvers for the STA25, I could have had an STA15 instead. We tried the two amps together and could not really detect any difference, I went for the greater power of the 25.
I have a pair of Quad II's as well, GZ32's in those, could run them to add to the heating!
Strangely enough, all those years ago when I swapped Tannoy 12" Silvers for the STA25, I could have had an STA15 instead. We tried the two amps together and could not really detect any difference, I went for the greater power of the 25.
I have a pair of Quad II's as well, GZ32's in those, could run them to add to the heating!
Yep,sound better than any halogen heater;) Cheers Mick
Strangely enough, all those years ago when I swapped Tannoy 12" Silvers for the STA25, I could have had an STA15 instead. We tried the two amps together and could not really detect any difference, I went for the greater power of the 25.
I have a pair of Quad II's as well, GZ32's in those, could run them to add to the heating!
Think the mid and top is better with the 15, the bass is better with the 25.
spendorman
12-02-2017, 21:16
Think the mid and top is better with the 15, the bass is better with the 25.
People have mentioned this over the years, but I wonder how true it is. What puts me off a bit with the STA15 is the GZ34, they seem to fail a bit too often. I wonder if it's really big enough for the 22 Watts (I think) per channel that the 15 can put out.
A lot of the modern day '34's are not up to the job,definately recommend a Mullard in there .Just my experience-plus I rest easier not worrying the rec is going to fail and poss taking out the mains tx
spendorman
12-02-2017, 21:30
A lot of the modern day '34's are not up to the job,definately recommend a Mullard in there .Just my experience-plus I rest easier not worrying the rec is going to fail and poss taking out the mains tx
I have several original Mullard GZ34's, bought years ago for the Quad II's. In fact the original GZ32's never failed and are still OK. One has to be a bit careful using 34's in the Quad II, even though I believe that Quad did. It raises the HT a bit, possibly putting more strain on the already almost marginal mains transformer. Did some tests years ago.
Always used Mullards and have stocked up on them.Have tried newer types that I have come across but to be kind ,lets just say they did nowt for the sound , sort of "dirtied" the sound and affected the sound stage image.[would never put a Chinese one in there] Just my two pennorth,ymmv
spendorman
14-02-2017, 13:30
I happen to have one in for service at the moment... Will add my subjective review when the work is completed... (I made a decision to not hear this legend until it's working A1). This will be the first time I've had the use of one in my own system.... known quantity.. known acoustics etc. I'm so hoping it won't be a let down to not just meet a hero but get to know him.. at least for a few days before it has to go back to it's lucky owner.
I'd be interested to hear what you find needs doing, mine has needed nothing in all the years that I owned it, well, I did put a little Servisol on the impedance selector wafer switches.
If the STA25 that you have is anything like mine, I don't think that you will have anything much to complain about with the sound quality.
It is normal that mains transformers on the STA25 III make a small amount of mechanical noise. This is not due to loose windings etc., but is due to hard switching of the solid state rectifiers.
A mod was devised early on that put a resistor in the HT circuit and that reduced the mechanical buzz to a very low level. This mod was soon incorporated into all new units.
Can be seen here:
https://flic.kr/p/S82CeV
Arkless Electronics
14-02-2017, 14:14
I'd be interested to hear what you find needs doing, mine has needed nothing in all the years that I owned it, well, I did put a little Servisol on the impedance selector wafer switches.
If the STA25 that you have is anything like mine, I don't think that you will have anything much to complain about with the sound quality.
It is normal that mains transformers on the STA25 III make a small amount of mechanical noise. This is not due to loose windings etc., but is due to hard switching of the solid state rectifiers.
A mod was devised early on that put a resistor in the HT circuit and that reduced the mechanical buzz to a very low level. This mod was soon incorporated into all new units.
Can be seen here:
https://flic.kr/p/S82CeV
This one has had a tough life.... It seems there was a major self immolation at some point and new Radford revival boards were fitted.... but not without this genius of an "engineer" deciding that the electrolytics didn't look right without the "stripe" ends all being the same way round... so some blown new electrolytics which didn't like being reverse biased for a start!:eek:
The work I'm doing pretty much consists of putting right the errors of the amateur pillock who had been at it before...
It already has that resistor fitted to the mains transformer but thanks for the info on that:)
Arkless Electronics
14-02-2017, 14:17
GZ34's do need to be good ones such as Mullard 9or the equally good Brimar, Mazda etc). In my modded stereo 20 Edicron branded GZ34's have a life of approx 3 days!!! Yes really.
I'll have to get round to fitting a silicon rectifier replacement on an octal valve base with suitable dropper resistors. Much better than valve rectifiers any way!
RothwellAudio
14-02-2017, 14:55
It's been so cold recently, thought that the extra couple of hundred watts or so of heat into the room would not be wasted.
I know I'm going off at a complete tangent here but I agree entirely - "waste" heat isn't wasted at all if heat in the room is desirable, which is usually the case in Britain in winter. Energy efficient lightbulbs are really only saving you money if they're used in a room that doesn't have any heating on.
Ok, back to Radfords ...
Arkless Electronics
14-02-2017, 15:24
I know I'm going off at a complete tangent here but I agree entirely - "waste" heat isn't wasted at all if heat in the room is desirable, which is usually the case in Britain in winter. Energy efficient lightbulbs are really only saving you money if they're used in a room that doesn't have any heating on.
Ok, back to Radfords ...
That's always been my take on it as well:)
I have a big issue with the way the energy companies were allowed to put up their prices a huge amount to offset the vast reduction in electricity consumption due to energy efficient bulbs! Their profits should have halved as too should the average electricity bill.
RothwellAudio
14-02-2017, 16:27
That's always been my take on it as well:)
I have a big issue with the way the energy companies were allowed to put up their prices a huge amount to offset the vast reduction in electricity consumption due to energy efficient bulbs! Their profits should have halved as too should the average electricity bill.
Yes Jez, and didn't they give away lots of free low-energy bulbs a few years ago? Like they really were free - we end up paying for 'em in the end, one way or another :lol:
12 calls a day or so repairing tv's ,vcr's in customers homes always made sure I had enough diodes and bridge recs in my toolbox Hardly a day went by when I did not need to replace some.In Thorn 3500 chassis used to connect 2 in series in p/s,if 1 went s/c hopefully the other didn't so saving a service call [used to blow when somebody switched the hoover on].Valve recs a lot more robust to mains surges/"dirty"mains spikes etc
Arkless Electronics
14-02-2017, 16:37
12 calls a day or so repairing tv's ,vcr's in customers homes always made sure I had enough diodes and bridge recs in my toolbox Hardly a day went by when I did not need to replace some.In Thorn 3500 chassis used to connect 2 in series in p/s,if 1 went s/c hopefully the other didn't so saving a service call [used to blow when somebody switched the hoover on].Valve recs a lot more robust to mains surges/"dirty"mains spikes etc
SS rectifiers will last indefinitely whereas valve ones predictably wear out and also have high series resistance. Thorn were not exactly known for over engineering...
Random (or not so random) blowing of diodes etc is entirely due to bad design practice.
walpurgis
14-02-2017, 16:44
SS rectifiers will last indefinitely whereas valve ones predictably wear out and also have high series resistance. Thorn were not exactly known for over engineering...
Random (or not so random) blowing of diodes etc is entirely due to bad design practice.
Many swear a valve rectifier allows the amp to sound better. Not sure how that can be though. It just rectifies.
Arkless Electronics
14-02-2017, 17:08
Many swear a valve rectifier allows the amp to sound better. Not sure how that can be though. It just rectifies.
As you would no doubt expect, I completely disagree.... Indeed it just rectifies and with vastly less losses than a valve rectifier.
Hi Jez the Thorn set was just an example,every type of tv was just the same .In theory ,ss devices should not go wrong but they do - changed thousands in my time -and in all sections of tv's etc-from s/c ,o/c and leaky/noisy In tech college in the 70's I remember the lecturer saying [and the older tech's at work] transistors etc would never need replacing as they wouldn,t go wrong.Just think valve recs can take more stick if something goes wrong somewhere else in circuit.If they sound better is another can of worms discussion to get into -myself ,I like the thought of valves Mick
spendorman
14-02-2017, 17:31
Yes, solid state transistors, rectifiers can fail at any time although there is no other fault in the circuitry. It's a rare occurrence, but does happen. Probably some latent fault in manufacture.
A lot of Germanium transistors have failed decades on due to tin whiskers.
Fairly recently one of my Quad 303's (of 1967 vintage) had a failure of one of the output transistors, strange as it had not been maltreated and nothing else was found to be faulty. The faulty transistor was replaced and all is fine again.
https://c1.staticflickr.com/9/8125/29704091785_5b6e030a3f_b.jpg (https://flic.kr/p/MfReBx)DSCF2277 (https://flic.kr/p/MfReBx) by A60man (https://www.flickr.com/photos/41679262@N02/), on Flickr
Transistors failed in tvs, as did valves..valves failed more i guess. Old tvs were not a great envioron for valves especially.. hot and dusty, valve bases always got dirty. Many homes were damp so arcing caused probs... big smoothing caps blowingwith messy results... hell youve no idea what you used to see inside some of those things.
Arkless Electronics
14-02-2017, 17:39
Hi Jez the Thorn set was just an example,every type of tv was just the same .In theory ,ss devices should not go wrong but they do - changed thousands in my time -and in all sections of tv's etc-from s/c ,o/c and leaky/noisy In tech college in the 70's I remember the lecturer saying [and the older tech's at work] transistors etc would never need replacing as they wouldn,t go wrong.Just think valve recs can take more stick if something goes wrong somewhere else in circuit.If they sound better is another can of worms discussion to get into -myself ,I like the thought of valves Mick
Hi Mick,
As you would expect I've changed thousands of faulty semiconductors myself also... Valves will take vastly more stick electrically than SS devices but the downside is they wear out... In consumer gear such as TV's the bottom line is pretty much all that matters for most makers! High voltage rectifiers have come on a bit since back in the day but it was always recommended to specify for many times the maximum voltage that could occur even in a fault situation. Best practice is to use strings of say 3 x 1N4007 1000V rectifiers for 240V mains, each with a resistor of around 220K and a capacitor of around 0.01uF across it. Two such strings replace a standard bi-phase valve rectifier used with a transformer with grounded centre tap. Done properly like this it should outlast the amplifier....
Similar strings with many more rectifiers are commonly used in valve RF power amps where they routinely work with 2500V for decades without trouble.
Obviously nothing is 100% reliable and just as with valves there will be the odd rogue failure... but usually far less often than with valves!
I agree about the bottom line, British electronics industry would have lasted longer if they had used better than bog standard components in the main[Hunts caps anyone].Also agree with valves wearing with use as in "the tubes gone" in the tv! crt's are only a type of valve.As I said ,I like the idea of valves just as some people like E-Types or Bonnevilles against modern cars /bikes [hands on fettling included;)
On about heat in tv's with valves,back in the 70's one model of Pye colour tv,-CT205 I think had an all valve line o/p stage.A common fult was a 100k resistor and a.1uf cap which went s/c.The pict would be lost and a few times the customer would sometimes wait for it to come back on ,all the time the PL509 was drawing more current and getting hotter and hotter.End result was the glass envelope melted leaving a sucked in hole in it."Oh no ,the picture went off and we switched it straight off" Now that is a room heater!:doh:
Arkless Electronics
14-02-2017, 19:08
On about heat in tv's with valves,back in the 70's one model of Pye colour tv,-CT205 I think had an all valve line o/p stage.A common fult was a 100k resistor and a.1uf cap which went s/c.The pict would be lost and a few times the customer would sometimes wait for it to come back on ,all the time the PL509 was drawing more current and getting hotter and hotter.End result was the glass envelope melted leaving a sucked in hole in it."Oh no ,the picture went off and we switched it straight off" Now that is a room heater!:doh:
I've only seen this happen the once personally.... A JJ EL34 fitted to a guitar amp...
spendorman
14-02-2017, 19:16
I've only seen this happen the once personally.... A JJ EL34 fitted to a guitar amp...
From what I read a while back, early JJ EL34's were not terribly reliable, they soon improved the situation. I have used JJ KT77's and EL34's in several amps, not had a failure, yet!
Arkless Electronics
14-02-2017, 19:34
From what I read a while back, early JJ EL34's were not terribly reliable, they soon improved the situation. I have used JJ KT77's and EL34's in several amps, not had a failure, yet!
I had so many problems with JJ valves over several years that I always recommend customers to give them a wide berth. I used to do a lot of work on guitar amps, which were usually valved, and I saw loads of early, random failures... I have heard rumours that quality has improved markedly over the last couple of years but I can't really comment from personal experience as I no longer supply valves and only do the odd guitar amp these days.
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