Just connected up an old friend, Radford STA25 III

[spendorman]

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.

[mik_rik]

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]

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]

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!
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]

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]

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]

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]

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

[mik_rik]

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]

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.