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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 10th Feb 2018, 12:00 am   #21
AC/HL
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Default Re: Armstrong 521 voltage selector

We're getting ahead of ourselves here, all cooperman needs at the moment is the selector plug. Any future problems can be dealt with if and when they surface.
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Old 10th Feb 2018, 11:34 am   #22
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Default Re: Armstrong 521 voltage selector

I think the link needed is between pins 3 and 4 for 240 volts (assuming the two primary windings need to go in series). I measured the resistances between the pins they seem to agree with the details listed earlier in the thread. They don't tally with the "official" diagram though. See attachment.
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Old 10th Feb 2018, 11:57 am   #23
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Default Re: Armstrong 521 voltage selector

Should work with a 3-4 strap as you suggest. You could insert it and check that to have 20R across the pins of the mains plug.
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Old 10th Feb 2018, 1:40 pm   #24
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Default Re: Armstrong 521 voltage selector

One step forwards - 2 steps backwards.
I added the link, the resistance was correct - so I powered it up without any of the PCBs. all looked good,mains indicator on. 54 volts a.c. on the transformer output.
Powered off, added the PSU card. Powered on, measured 73 volts across the main reservoir cap. Circuit diagram says 70 volts - so pretty close to where it needs to be. A few minutes later, a slight pop, then the RCD on my electricity supply activated. Tried running the amp without the PSU card, and again after a few minutes the mains tripped. Given that there is nothing connected to the transformer (apart from the power on light ) I'm thinking that the transformer is leaking current to earth when it has been on for a few minutes.

Oh - and the circuit diagram - it shows the main cap connected to the input side of the diode bridge - directly connected to the transformer. It surely should be shown connected to the output side.
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Old 10th Feb 2018, 1:44 pm   #25
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Default Re: Armstrong 521 voltage selector

Could be a leak in the mains suppression capacitors. Try disconnecting them.

EDIT. I see that all three capacitors are combined in one component. Disconnect the earth/chassis connection to it.
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Old 10th Feb 2018, 2:05 pm   #26
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Default Re: Armstrong 521 voltage selector

I'm just slightly ahead of you! I cut off the earth lead to the Plessey filter. Powered on and after a few more minutes, a slight pop - but the mains stayed on. Several more minutes and then the filter popped again - smoke this time. It's in the bin now!
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Old 10th Feb 2018, 9:25 pm   #27
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Default Re: Armstrong 521 voltage selector

Amplifier is now working. Quite powerful it is too.

.Suppressor cap needs replacing - I've not managed to find one small enough though - I can only find large ones for washing machines - any suggestions anyone?

Two further problems to sort out:-
1. The 400mA main fuse keeps blowing. I've put a 1 amp fuse in for now - I'm wondering if the 400mA suggested is incorrect?
2. The phono sockets are badly corroded, any suggestions for cleaning them - particularly the inside of them. Ideally I'd replace them - but they are panel mounted in strips of 5 - I doubt if I'll source any.
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Old 10th Feb 2018, 9:35 pm   #28
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Default Re: Armstrong 521 voltage selector

Quote:
2. The phono sockets are badly corroded, any suggestions for cleaning them - particularly the inside of them. Ideally I'd replace them - but they are panel mounted in strips of 5 - I doubt if I'll source any.
De Oxit and a cotton bud.
Or even meths or isopropyl alcohol and a cotton bud.

I use De Oxit and although expensive, I am on the same can I bought 3 years ago at a swapmeet.

A.
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Old 10th Feb 2018, 9:57 pm   #29
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Default Re: Armstrong 521 voltage selector

Quote:
Originally Posted by cooperman View Post
Suppressor cap needs replacing - I've not managed to find one small enough though - I can only find large ones for washing machines - any suggestions anyone?
Class X cap L to N.
Class Y cap L to E.
Class Y cap N to E.

I suggest 0.1uF 275V.
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Old 11th Feb 2018, 11:36 am   #30
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Default Re: Armstrong 521 voltage selector

I found one in a single package
https://www.ebay.co.uk/itm/Safety-ca...gAAOSw86JabLYh
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Old 11th Feb 2018, 12:51 pm   #31
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Default Re: Armstrong 521 voltage selector

Quote:
Originally Posted by bikerhifinut View Post
Quote:
2. The phono sockets are badly corroded, any suggestions for cleaning them - particularly the inside of them. Ideally I'd replace them - but they are panel mounted in strips of 5 - I doubt if I'll source any.
De Oxit and a cotton bud.
Or even meths or isopropyl alcohol and a cotton bud.
I use De Oxit and although expensive, I am on the same can I bought 3 years ago at a swapmeet.
In really stubborn cases I am not afraid to say that I have used a 1200 grade Wet'n'Dry paper wrapped around a very small (Watchmaker's) screwdriver (not a Bradawl as they are tapered) - and/or - the edge of a brand new Stanley Knife blade to gently scrape the dross off. Very effective.
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Old 11th Feb 2018, 1:36 pm   #32
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Default Re: Armstrong 521 voltage selector

Quote:
Originally Posted by cooperman View Post
Well done for finding that.

I've nothing against eBay, but I wonder if any of the big suppliers stock them?

It's very hard to search for class X and Class Y caps on the RS website.
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Old 13th Feb 2018, 1:39 pm   #33
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Default Re: Armstrong 521 voltage selector

Has anyone any comments about the 400mA main fuse that keeps blowing. As mentioned I've temporarily used a 1A fuse in. Amplifier has had a good 3 hour test on fairly high volume without any issues. I'm not really happy with more than doubling the value of the fuse though.
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Old 13th Feb 2018, 3:42 pm   #34
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Default Re: Armstrong 521 voltage selector

The manual is quite clear that the mains fuse should be just 400mA anti-surge.
You might check the standing currents in the output transistors (remove fuses and insert ammeter). They should be somewhere around 50mA per channel, with a regulated HT of 50V.
And I would remove completely the mains surge suppressor. It has a tendency to explode(!) and might be leaking and causing the primary fuse to blow.
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Old 13th Feb 2018, 11:41 pm   #35
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Default Re: Armstrong 521 voltage selector

The mains surge suppressor has already been removed - see earlier posts. The PSU fuses are rated at 1 amp - if the regular current is only 50mA - surely the rating seems a bit high? I wonder if anyone has any "real world" experience with this model and can confirm that 400mA main fuse is working as per the manual? I know from bitter experience that manuals are not always accurate.

I'll carry out the measurements an report the details.
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Old 14th Feb 2018, 12:26 am   #36
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Default Re: Armstrong 521 voltage selector

100mA total standing current but 1-2A peak to get 25W
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Old 17th Feb 2018, 2:34 pm   #37
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Default Re: Armstrong 521 voltage selector

I put the 400mA fuse back in (replacing the temporary 1 amp). Everything seems to be working perfectly now. I think the issue was the suppressor capacitor. Initially it was tripping the mains, so I disconnected the earth lead from the component. That stopped the mains from tripping, but he fuse blew when I ran the amp with the audio pcbs installed. At that time I assumed tie pcbs were drawing more current than usual and hence blowing the fuse. I then (temporarily) upped the fuse to 1 amp. Eventually the suppressor went pop - so i removed it entirely. I didn't realise at the time that it was the combined pcb and faulty suppressor that was overloading the fuse. Now with no suppressor, a 400mA fuse is sufficient - as per the specification.
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Old 20th Feb 2018, 1:20 am   #38
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Default Re: Armstrong 521 voltage selector

I've been putting the repaired amplifier through it's paces. Loud -Led Zeppelin, soft - Nina Simone. All fine at first - now starting to get soft popping noises in one channel. Like someone blowing on a microphone. Any ideas?
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Old 20th Feb 2018, 9:47 am   #39
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Default Re: Armstrong 521 voltage selector

Moderator - do you think it would be best to open a new thread for this? The issue with the voltage selector was solved several posts back.
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Old 20th Feb 2018, 10:37 am   #40
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Default Re: Armstrong 521 voltage selector

Please continue the current thread.
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