• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Radford STA-15 questions

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patrickamory

Member
Joined 2007
matadorrecords.com
I just acquired a Radford STA-15 amp. I was wondering whether anyone could help me with some questions:

- Voltage selector. I'm in the US. There is a voltage selector switch, but it's confusingly marked with 3 settings:

110/220
125/235
140/250

I want 110, obviously, not 220... but I can only choose the combination, whatever that means. Does anyone know why both voltages are marked at the same position on the selector switch? Am I safe to plug it in at 110/220 in a 110V mains system?

- Has anyone restored one of these before? Any tips - obvious parts for replacement, etc.? The amp seems to be completely original.

- Does anyone have owner's manual, schematic or service manual for one of these?

Thanks in advance -

Patrick
 
Tom Bavis

Tom Bavis

Member
Joined 2002
audiophool.com
Actually 125 is a better choice - most places have in excess of 120V these days. The 125 / 235 selection is done with an internal soldered jumper. Unless this amp came from Europe, it's probably on the lower setting. You can't hurt it with lower than rated voltage, anyway ,but I'm sure a LOT of US equipment has gotten fried on 230v!

Schematic: http://www.drtube.com/schematics/radford/sta15.gif
 
kevinkr

kevinkr

Administrator
Joined 2004
kta-hifi.net
Paid Member
Yeah, you'll have to change some internal jumper settings to get it to work here.

Remove the connection between PY2 and PY3

Connect PY1 to PY3

Connect PY2 to PY4

The above is probably obvious to you, but in case it wasn't.. ;)

IIRC these are hardwired connections that you will have to solder.. (It's been a while since I saw one of these.)

Change the fuse to 3A, medium blow type if possible.

Finally set it to the 125V position on the voltage selector switch, better to slightly under run the amp voltage wise than to significantly over run it.

How old is the unit and are you sure the electrolytics are all copacetic?
 
P

patrickamory

Member
Joined 2007
matadorrecords.com
Argh, the label on the power transformer primaries turns out to be gone. It survives on the secondaries side.

On the secondaries, the tap numbers go 13-18 from bottom to top on the left, and 19-24 top to bottom on the right.

Does this order give any clue as to how the primary taps must have been numbered?

Here's a couple of pics:

1. secondaries:

An externally hosted image should be here but it was not working when we last tested it.


1. primaries:

An externally hosted image should be here but it was not working when we last tested it.


anyone have any idea?

Patrick
 
7N7

7N7

Member
Joined 2003
What a delightful thread! I am pleased to hear that the amplifier works well.

Just want to add that I think that had he lived later, Arthur Radford could have done well in today's computer industry.

His talent for making things difficult, if this story is typical, would have been most appropriate!

7N7
 
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bigwill

Member
Joined 2004
Shame my father wasn't there to help - I THINK he actually knew Arthur personally and when they closed down he ended up with many many of the parts for most of the amplifier range and continued to build and sell them. He is friends with John Widgery who started woodside electronics, too.
 
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