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Radford STA25 Mk III -- a lot of questions.

That's an interesting question, because that one doesn't have a mark on it as far as I can see saying what it is. It came up when I was speaking to Nick at Emporium/. The EF86 valves are clearly marked.

Is there something I can read about valves, a sort of Idiot's Guide?
 
mandryka said:
I was hoping for something a bit more . . . lyrical, poetic.

Something which will explain in words of one syllable and pictures but NO diagrams about order of the little valves etc.

Something that begins

"Congratulations on buying the Radford STA25, the world's greatest amplifier . . ."
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Don’t forget this is from the mid 60’s, when you were supposed to put the switches in the right position, bung it in a cupboard and forget about it for the rest of its life. Making claims like that would probably have been considered very brash and ungentleman-like! I don’t think lyricism and poetry came in until companies began to notice the marketing was as important as the engineering.
 
mandryka said:
That's an interesting question, because that one doesn't have a mark on it as far as I can see saying what it is. It came up when I was speaking to Nick at Emporium/. The EF86 valves are clearly marked.

Is there something I can read about valves, a sort of Idiot's Guide?
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Hmm... they should be 6U8 but there are others that will work in that position and are more readily available, not that the 6U8 is particularly hard to get, but ECF82 is far more common in UK and I believe that there are others which may work.... when I last had one in I did a little experiment and tried an ECF82 in place of the correct 6U8 and although it still worked fine the THD went up from a fantastically low 0.035% to about 0.5%
Even with the "identical" two 6U8's the one from the channel that had been blown up measured about 0.08% but I didn't notice any issues subjectively.

I guess there's not much that would be particularly useful to you as far as books on valves go... they tend to be either historical or technical and much of the stuff on line is more of the subjectivist stuff and often on the usual suspects such as EL34, ECC83 etc, often from a guitar players POV also. It's all out there on line if you spend enough time looking for it of course and in fact most of the "bibles" on the subject are available to download FOC.

I can't think of anything along the lines of a "I've just bought my first valve hi fi amp. What do I need to know?" type books though.

FYI the EF86 is a low noise pentode, the 6U8 is a triode pentode ie two separate valves in one envelope and the EL34 are output pentodes.
 
mandryka said:
That's an interesting question, because that one doesn't have a mark on it as far as I can see saying what it is. It came up when I was speaking to Nick at Emporium/. The EF86 valves are clearly marked.

Is there something I can read about valves, a sort of Idiot's Guide?
Click to expand...

Can you see what make they are? 6U8 likely to be an American brand but ECF82 likely to be Mullard and if not then a European brand.
 
Should I turn it off when not in use, or can in be left on for a few hours? I don’t mind turning it off when sleeping but given it only reveals its full majesty after half an hour of warming up, it would be nice not to have to anticipate the whim to listen to it.

Having said that I’ve just put it on and it sounds ****ing great after 5 minutes!

(Just found extended discussion of this thorny question here

https://forums.stevehoffman.tv/threads/leave-tubes-on-all-the-time.394223/

I shall buy a CO2 fire extinguisher tomorrow!)
 
mandryka said:
Should I turn it off when not in use, or can in be left on for a few hours? I don’t mind turning it off when sleeping but given it only reveals its full majesty after half an hour of warming up, it would be nice not to have to anticipate the whim to listen to it.

Having said that I’ve just put it on and it sounds ****ing great after 5 minutes!
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The one I rebuilt etc sounded great as soon as it had warmed up after a minute or so and I can't say I noticed it improve after that...

You really need to be switching it off when not in use as the valves wear whilst switched on, especially the output valves. Obviously you don't need to be switching it off when making a coffee or going to the lav but if you keep leaving on for an hour or two a day just in case you want to listen to it later then you will be spending a lot with EL34 suppliers!
 
Are you using it with the Spendors then? I used the one I had in with my very similar BCII's and it sounded great! I'd be interested to know your views on STA25 V's KSA50!
 
I am really pleased it is working.
... out of interest, did you put the EL34s (the big ones) back in their original places? Maybe they were marked as to location?
If not you might want to check the 2 volt bias settings on each one.

I would not leave it on, switch on 15 to 20 minutes before you want to listen, switch off after. They do get toastie after 5 or 6 hours... and if anything untoward happens you will be there to pull the plug. Enjoy it.
 
snowman_al said:
I am really pleased it is working.
... out of interest, did you put the EL34s (the big ones) back in their original places? Maybe they were marked as to location?
If not you might want to check the 2 volt bias settings on each one.

I would not leave it on, switch on 15 to 20 minutes before you want to listen, switch off after. They do get toastie after 5 or 6 hours... and if anything untoward happens you will be there to pull the plug. Enjoy it.
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/\ Very good point!
 
So great that it turned out good for you (fingers crossed!).
When I discussed my EAR 516 after a service with Tim de Paravicini, he told me to do the same with the EAR 516. Turning it off would make for another trouble-free 10 years on an amp that according to Danish "urban myth" had a tendency to explode. Once you have had a look under the hood of the EAR 516 which reveals an extremely tight-packed power amp, you understand that only a fool would rack mount it. I can only imagine how hot it will be if trapped in a studio rack and how it will eventually burn burn burn.
 
snowman_al said:
I am really pleased it is working.
... out of interest, did you put the EL34s (the big ones) back in their original places? Maybe they were marked as to location?
If not you might want to check the 2 volt bias settings on each one.

I would not leave it on, switch on 15 to 20 minutes before you want to listen, switch off after. They do get toastie after 5 or 6 hours... and if anything untoward happens you will be there to pull the plug. Enjoy it.
Click to expand...


They weren't marked unfortunately. At the moment I don't want to take out the EL34s because I had such a lot of trouble putting them in! I intend to get it serviced very soon, which hopefully will sort out these problems. I just want to enjoy it for a few weeks, a month, and then I'll get it serviced.
 
Arkless Electronics said:
Are you using it with the Spendors then? I used the one I had in with my very similar BCII's and it sounded great! I'd be interested to know your views on STA25 V's KSA50!
Click to expand...

Spendors are upstairs with Mr. Krell, Rogers are downstairs with Raddy. I will swap around and play around soon. Next week.
 
mandryka said:
They weren't marked unfortunately. At the moment I don't want to take out the EL34s because I had such a lot of trouble putting them in! I intend to get it serviced very soon, which hopefully will sort out these problems. I just want to enjoy it for a few weeks, a month, and then I'll get it serviced.
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You don't need to take them out... you just need a screwdriver and a multimeter. the controls are on the back and there are holes to put a screwdriver through to adjust them, one per output valve. Adjust for 2V at the test points after it's been on for half an hour or so. You don't need to take the bottom off or anything.

As the valves were not marked and are in random sockets it is worth doing. It only takes a couple of minutes.
 
That one is fine. You will need to check the 'bias' from time to time as the large valves will change from being used. Radford made it really easy as Jez says in #194.
 
JR149s, like LS3/5As are closer to 15 Ohm, I find the Stereo 20 sounds best on the 16 Ohm tap. Basically try both, pick the one that sounds best!
 
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