Pye P224: Advice Please.

[Joe]

When I got my Pye P224 out of the loft last week I'd expected to be doing far more work on the cabinet than the electronics but then found it was in a much better state than I'd remembered so I cracked on with the guts.

It appeared to have not been 'Got at' but must have had some attention in the past as all the valves are Mullards except for the EBC81 which is a Brimar. Besides that one of the dial lamps was a 3.5V one which, not surprisingly, was o/c.

There were no waxies and the big electrolytics tested OK, leaking less than a milli-amp when seriesed up with the mains, a silicon diode, a 15W lamp and 1K resistor.

There were two other electrolytics which were leaky so I decided to change them along with a Hunt's job that looked a bit mis-shapen.

I went to my local electronics shop yesterday for the bits for this along with a load of resistors for my Little Maestro. I have been using that shop for years and always get good service but unfortunately I got somebody yesterday who didn't seem to have much idea and when I got home I discovered that the resistors were far too puny so marched them back and one of his colleges sorted them out.

When I got on with the Pye I found that I hadn't got a 0.05 uFcapacitor to replace the Hunt's. I know I'd confused this chap in the shop a bit by forgetting to convert a few of the values to modern 'Preferred' ones so can't be too hard on him. After a hunt (no pun intended) I found 2 0.022s and a 0.01 so I paralleled this lot up.

When I first switched on I was pleased by the lack of hum but this because concern when stony silence continued to prevail so I thought I'd better check that the valves were glowing. I then remembered that I hadn't put them back! I re-fitted these, though not the EM81 as I can't find it. All seemed well after that but I didn't play about for long as I was wanting my bed.

I gave it a longer test this morning. With the volume right down there's certainly a hum but I don't know if this is only at a level which is to be expected, it certainly isn't a problem.

The reception seemed good, in fact on strong signals like Radio Sheffield the volume only needs to be just off the stop.

However, when it had been on for ten minutes or so the output took on a certain sub-aqua quality: it sounded like the announcer or singer was gargling and this was getting worse.

The big electrolytics were still stone cold but I don't know if that means anything or not.

I'd appreciate any advise on what the likely cause of this is as, for all I know, it's something common and obvious. Please bear in mind that my knowledge is slight so replies like "It's a duff output cathode by-pass capacitor" aren't going to be a lot of use.

You SHOULD be able to see photos by clicking this link:-

http://cid-132b7a4e6cdebd02.skydrive.live.com/redir.aspx?page=play&resid=132B7A4E6CDEBD02!141

Thanks in advance

- Joe

[Steve_P]

For values such as 0.05uF, pick the nearest preferred value. 0.047uF will be fine.

Smoothing capacitors should not get hot. If they are new, then they are faulty or badly soldered. If they are the old ones, change them. Very common problem.

Have you got the circuit?

Cheers,

Steve P.

[Joe]

The smoothing capacitors are NOT getting hot. I've got one spare one which I'll try and also take what measurements I can.

As for the circuit/service data, Mark kindly provided a Radio Servicing scan. There isn't much information on that beyond the circuit diagram and alignment info. Also it's so small that it's difficult to read some bits. I haven't been able to track down either a Trader or ERT sheet at any price.

Oh well, it would be boring if it was too easy and at least nothing's gone bang. Yet.

Thanks for the replies so far as at least it's given me an area to concentrate on.

[Steve_P]

There are 2 other possibilities here. One is a heater cathode short inside a valve, more than likely the EL84, which is an output valve which does get hot. It could have been killed by 'That Capacitor'. In this case C44 and C45.

The other possibility is the PCB having gone conductive. This is nasty, Try scraping the top of the PCB in between the tracks, this sometimes works.

Cheers,

Steve P.

[Joe]

A PCB going conductive certainly does sound nasty. It LOOKS fine and I've given it a scrub with a tooth-brush.

As soon as the set had warmed up to the point of playing there was a voltage drop of 229V across C48 and 198V across C47. By the time it started to sound really ropey these had dropped to 198V and 185V.

I've tried changing each of these for the new one and used the each of the old ones with this. It did seem to lower the initial hum but the distortion and voltages are about the same. It certainly seems worth getting another new capacitor to try. The only bogey is the 'bus fare going to fetch one but I'll be out and about in a couple of weeks so can get one then.

If it is this heather-cathode short shall I get it 'round the back of the computer monitor and "Crack it one with the EHT?" It could well be that as it does get worse as it warms up.

I'll keep fiddling and report and changes.

Thanks again for the help so far, lads.

All the best

Joe

[Steve_P]

No, don't do anything like that!!!!

EL84 valves are easy to get hold of. Try here...

http://www.crowthornetubes.com/contents.htm

Cheers,

Steve P.

[Joe]

Right, I've now tried it with the brand new capacitor along with the good section (or at least the section I believe to be good) from the can of my Little Maestro. This seemed to reduce the hum but not the distortion. I'll hold off buying another valve until I've tried it with two new capacitors and I'll also change C44 and C45 as if they've damaged the old one I don't want them to do likewise to the new one. With a bit of luck I may be able to borrow a valve as a mate of mine has several valve radios.

Thanks for the tip about e-Bay, Jamie. The trouble I find with getting this sort of thing mail-order is that I can never seem to get everything I want from the same place so end up getting clobbered for multiple postage charges. For instance Crawthornes do capacitors but not resistors and Savoy Hill do resistors but have stopped doing capacitors.

I'm not in a rush and ought to put it aside for a while as there's other things I should be doing, like finishing plumbing the new radiator in in my living room.

I'm certainly enjoying myself and have overcome my fear of the 'high' voltages involved. My den looked like a proper mad scientist's lab earlier:-

[attachment=624]

Thanks for the assistance; I wouldn't even have taken it on if I hadn't known that I could shout for help.

All the best

Joe

[Mark R]

Joe
the distortion you describe, like being underwater, sounds familiar, try a valve a Steve suggests, but this set has a mains transformer right?

cheers Mark

[Joe]

It HAS got a mains transformer and the voltage selector is on 221-250V

[Mark R]

Joe

are you using a 2 core mains cable? Live and neutral?

cheers Mark