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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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7th Feb 2018, 4:32 pm | #1 |
Pentode
Join Date: Feb 2018
Location: Cheshire, UK.
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Armstrong 521 voltage selector and fuse blowing issues.
I've just acquired a rather battered Armstrong 521 that I'm about to try to restore. It is missing the octal plug from the back of the unit that selects the correct voltage. I doubt if I'll find a replacement for such an old item - but i wondered if anyone has a diagram of it's internal connections. I could either fabricate a new plug - or I could solder the correct links inside the unit.
Also does anyone know the value of the mains fuse (on the back panel) and also the two fuses on the PSU PCB? Thanks in advance! Last edited by cooperman; 7th Feb 2018 at 4:47 pm. |
7th Feb 2018, 5:34 pm | #2 |
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Re: Armstrong 521 voltage selector
I offered a couple of octal plugs in post #16 in this thread:-
https://www.vintage-radio.net/forum/...d.php?t=131297
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
7th Feb 2018, 8:31 pm | #3 |
Dekatron
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Re: Armstrong 521 voltage selector
Are you sure it’s an octal plug? It will only have one position and would need to be re-wired to suit other voltages, which is not a user option. It may be an octal looking socket but have a plug with no keyway and a single shorted link.
A photo of the socket would help. The circuit diagram should show what it is. |
7th Feb 2018, 11:49 pm | #4 |
Octode
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Re: Armstrong 521 voltage selector
If my memory isn't mistaking me I think the Armstrong 500 series had a noval (B9A) voltage selector?
A. |
8th Feb 2018, 12:43 am | #5 |
Dekatron
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Location: Heckmondwike, West Yorkshire, UK.
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Re: Armstrong 521 voltage selector
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8th Feb 2018, 1:06 am | #6 |
Heptode
Join Date: Jan 2006
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Re: Armstrong 521 voltage selector
Yes, a search of the internet brings up pictures of the back of the 521 and it is a noval socket but I don't know where you would find the appropriate plug. Another search brings up a copy of the user manual on Saturn Sound which has a page detailing the the specs of the fuses. There could be a copy of the circuit diagram out there too, but it's late...
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8th Feb 2018, 1:08 am | #7 |
Heptode
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Re: Armstrong 521 voltage selector
Oops, crossing posts there!
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8th Feb 2018, 9:44 am | #8 |
Pentode
Join Date: Feb 2018
Location: Cheshire, UK.
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Re: Armstrong 521 voltage selector
Maybe the term Octal is incorrect. It looks like a valve socket - as per this link
https://modulusamplification.com/Val...-P1314630.aspx It is shown on the circuit diagram at this liink. http://www.audiomisc.co.uk/Armstrong/500/diags/Z17.gif |
8th Feb 2018, 10:27 am | #9 |
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Re: Armstrong 521 voltage selector
That's a B9A nine pin valve holder. The plug that fits it must have a limited number of pins so that it can be fitted in more that one position without a pin fouling the gap.
The links drawn in the circuit diagram would result in no connection to the neutral side of the incoming mains supply. If you're planning to hard wire it I suggest connecting all the turns on the primary winding in series ie for a 240VAC supply.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
8th Feb 2018, 10:44 am | #10 |
Pentode
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Location: Cheshire, UK.
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Re: Armstrong 521 voltage selector
I wonder if anyone else in this forum has an identical amplifier and whether they would be kind enough to check with a meter which pins are connected in the selector plug?
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8th Feb 2018, 11:01 am | #11 |
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Re: Armstrong 521 voltage selector
Looking at the diagram it's not clear which way the pins of the socket number. Assuming they number clockwise, the wring is as follows:-
Live - pin 8 - LA4 - pin 5 - pin 3 - LA5 - pin 9. From pin 9 the wiring goes nowhere, so you'll need a link from pin 9 to pin 7 which goes to neutral.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
8th Feb 2018, 12:10 pm | #12 |
Dekatron
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Re: Armstrong 521 voltage selector
Do we know what voltage the circuit diagram is set for? On most amps the normal way would have the windings in series for 240 v and parallel for 115 v.
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8th Feb 2018, 12:59 pm | #13 |
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Re: Armstrong 521 voltage selector
As drawn, the circuit diagram isn't set for any voltage. There's no circuit through the primary windings.
Given that the picture shows a selector plug with a highest voltage of 240 VAC, I've assumed that all the primary windings will need to be connected in series to achieve this.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
8th Feb 2018, 1:45 pm | #14 | |
Nonode
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Re: Armstrong 521 voltage selector
Quote:
Fuses: F1 and F2 (LT) 1A (normal) F3 (Mains) 400mA anti-surge Mains selector: PM me as I have a box with lots of spares from a couple of 500 series machines I parted out to help mend my collection, a few years ago. I know I have a mains transformer there, with the selector still attached. Good luck with the repair.
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8th Feb 2018, 2:31 pm | #15 | |
Pentode
Join Date: Feb 2018
Location: Cheshire, UK.
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Re: Armstrong 521 voltage selector
Quote:
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8th Feb 2018, 3:52 pm | #16 |
Dekatron
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Re: Armstrong 521 voltage selector
Your best bet will to be to contact Jeremy, all you need is the plug part of the selector. It should be captive I'd have thought, but it obviously can be detached somehow. This will save a lot of messing about and keep the approvals.
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8th Feb 2018, 4:55 pm | #17 |
Heptode
Join Date: Dec 2016
Location: Sheffield, South Yorkshire, UK.
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Re: Armstrong 521 voltage selector
I am certain I have same model in the loft. It has blown the output transistors. When I looked around for replacements they were about £50 each! So I gave up.
Interesting amp though. I remember the tone controls affected the recording of music. So you could increase the bass or treble on the recording! |
8th Feb 2018, 5:10 pm | #18 | |
Nonode
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Re: Armstrong 521 voltage selector
Quote:
I have checked the pins out on the circuit and in practice and for future reference here's the information. (I hope I have it right!). There are only 4 pins on the plug, and it is not captive. The diagram below shows how the pins are wired in pairs. The diagram definitely shows the pins looking at the REAR of the socket from inside the equipment. (Like looking at the back of a B9A valve base). As shown, with pins 7 and 9 linked on the socket, the amp will work from 240V mains. So the B9A socket wiring (with colours) is: Pin 1 n/c Pin 2 n/c Pin 3 (Pink) first primary winding high tap Pin 4 (Grey) second primary winding low tap Pin 5 (Blue) second primary winding high tap Pin 6 (Yellow) first primary winding low tap Pin 7 (Orange) Linked to Pin 9 Pin 8 (Green) Live in, and second primary winding (L44) start Pin 9 (Orange) Neutral in, and first primary winding (L45) start Jeremy
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Jeremy, G8MLK, BVWTVM Friend, VMARS, BVWS Secretary. www.pamphonic.co.uk www.bttt.org.uk Last edited by Pamphonica; 8th Feb 2018 at 5:17 pm. |
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8th Feb 2018, 5:12 pm | #19 | |
Nonode
Join Date: Mar 2008
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Re: Armstrong 521 voltage selector
Quote:
1. Put in OC28s. Lower ft but probably not noticeable. 2. Search on this forum for threads about replacing the transistors with more modern silicon equivalents.
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9th Feb 2018, 9:38 pm | #20 |
Octode
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Re: Armstrong 521 voltage selector
there are a no of articles re fitting silicon devices in the archive
you can do the repairs for a fiver Trev |