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Old 15th August 2003, 03:48 AM   #1
Gram is offline Gram  New Zealand
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Default Radford STA25

My Radford is well due for a general overhaul. Does anyone have any suggestions for mods? Just thought I'd ask before I replace components with original values, etc...Thanks
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Old 15th August 2003, 04:31 AM   #2
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What are you wanting to do with it? Mod for best sound, or keep as a collector peice? If it's as a collector item, don't touch anything that doesn't need to be touched.

Should you want to mod it, there are three options IMO;

1) take the OPTs and build a new amp around them on a new chassis.

2) as you modify, take photo's, and carefully bag and mark the changed components so you can put it all back together the way it was later if you so choose.

3) don't worry at all and hack it into whatever you want.

I'd go for (1) and build a non FB, non UL design of some sort around the reputedly excellent OPTs, and maybe PT. And probably not use EL34's.
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Old 15th August 2003, 04:39 AM   #3
Gram is offline Gram  New Zealand
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Default Radford STA25

Oops..sorry. This is a 25 yr-old copy of a Radford with twin power supplies. I was told the OPT's are very well built..and it sure sounds nice. The issue of keeping it original doesn't really come into it..Thanks for your reply.
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Old 15th August 2003, 05:31 AM   #4
SHiFTY is offline SHiFTY  New Zealand
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Hey another kiwi! Welcome !

With your amp, you should replace the coupling caps if they are the wax paper type. According to the schematic at http://www.drtube.com/audioamp.htm#Radford they should be around 0.47uF.

Also you might want to check the values of resistors, they tend to drift over time... In particular the anode resistors, power supply resistors and cathode resistors.

If you want to, replace the cathode bypass capacitors with newer versions. I have found the Hitano bi-polars from Dick Smiths are good sounding. Power supply caps tend to last pretty well, those old cans are pretty good. If they don't get warm they are ok.

If the amp sounds good and still has some volume, the valves are probably ok.

If your amp uses solid state diodes in the HT power supply, you might want to replace them with UF4007s (available from Jaycar in AK.)

Other than that, check the valve pins and sockets for corrosion, tug all solder joints and generally look for anything crappy. Check there is a mains fuse (!)

Good luck!
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Old 15th August 2003, 09:32 PM   #5
Gram is offline Gram  New Zealand
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Default Radford

Thanks for those suggestions..and Hey Shifty..
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