Radford STA-15 questions

patrickamory · 29th July 2007, 07:57 PM

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 · 29th July 2007, 08:19 PM

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

patrickamory · 29th July 2007, 08:21 PM

Ah, great, thanks for the schematic link!

Sorry to be dense, but do I need to go inside and move the jumper then?

I've measured about 117V at my outlet...

Patrick

Tom Bavis · 29th July 2007, 08:33 PM

Where was it last used? If US or Canada, it's set for 120V. What plug is on the cord?

patrickamory · 29th July 2007, 09:09 PM

In the UK. No plug on the cord. I'm sure it's set for European voltage.

kevinkr · 29th July 2007, 11:47 PM

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?

patrickamory · 29th July 2007, 11:52 PM

Thanks Kevin, I'll get to work. Amp is probably early '70s and the 'lytics may well need replacing. I noticed the fuse rating issue too. Thanks!

patrickamory · 30th July 2007, 07:20 PM

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:

1. primaries:

anyone have any idea?

Patrick

patrickamory · 30th July 2007, 08:14 PM

Ah - got it - by tracing the wiring from the voltage selector. I could barely see the jumper between PY2 and PY3 (it's invisible in the photo above) - I've now identified the taps.

Patrick

patrickamory · 30th July 2007, 09:14 PM

Up and playing music through my Quads. Thanks Tom and Kevin.

Next step: replacing the EL34s, and component check.

Patrick

29th July 2007, 07:57 PM	#1
patrickamory diyAudio Member Join Date: Jun 2007	Radford STA-15 questions 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

29th July 2007, 11:47 PM	#6
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	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? __________________ www.kta-hifi.net

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Radford SPA-60 schematic wanted	audiomatic	Solid State	4	17th October 2010 06:01 PM
Radford ZD 50 and ZD 100 schematic anyone ?	phase_accurate	Solid State	9	20th February 2009 11:16 AM
Need help with a Radford HD 250 amplifier	gaetan8888	Solid State	2	4th July 2007 05:59 PM
Wanted Radford MA-15	spoke	Tubes / Valves	6	14th June 2007 03:29 AM
Radford STA25	Gram	Tubes / Valves	4	15th August 2003 09:32 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

29th July 2007, 08:19 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	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

29th July 2007, 08:21 PM	#3
patrickamory diyAudio Member Join Date: Jun 2007	Ah, great, thanks for the schematic link! Sorry to be dense, but do I need to go inside and move the jumper then? I've measured about 117V at my outlet... Patrick

29th July 2007, 08:33 PM	#4
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	Where was it last used? If US or Canada, it's set for 120V. What plug is on the cord?

29th July 2007, 09:09 PM	#5
patrickamory diyAudio Member Join Date: Jun 2007	In the UK. No plug on the cord. I'm sure it's set for European voltage.

29th July 2007, 11:52 PM	#7
patrickamory diyAudio Member Join Date: Jun 2007	Thanks Kevin, I'll get to work. Amp is probably early '70s and the 'lytics may well need replacing. I noticed the fuse rating issue too. Thanks!

30th July 2007, 07:20 PM	#8
patrickamory diyAudio Member Join Date: Jun 2007	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: 1. primaries: anyone have any idea? Patrick

30th July 2007, 08:14 PM	#9
patrickamory diyAudio Member Join Date: Jun 2007	Ah - got it - by tracing the wiring from the voltage selector. I could barely see the jumper between PY2 and PY3 (it's invisible in the photo above) - I've now identified the taps. Patrick

30th July 2007, 09:14 PM	#10
patrickamory diyAudio Member Join Date: Jun 2007	Up and playing music through my Quads. Thanks Tom and Kevin. Next step: replacing the EL34s, and component check. Patrick

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)