Deterioration of Pye control knobs.

[rigsby27]

Hello all,

I'm putting the finishing touches to a refurbed Pye 75, I washed the four knobs in warm soapy water but when dry they look white?

It's difficult to explain the appearance but it's like a concentrated mildew sort of colour/effect, I have used a nail brush and foam cleaner and they have cleaned up slightly but not 100%.

Can anyone explain what's happened please? and how to clean this sort of plastic in the future.

Thanks for your time,

Tony.

[Phil G4SPZ]

Tony,

Have you tried Brasso or a similar (very) mild abrasive cleaning fluid?

Good luck,

Phil

[Radio_Dave]

Hi Tony,

If you really want to know... It's, probably, the grease from years of mucky fingers on the knobs, emulsifying with the water you are washing them in .

Try washing them more vigorously or, as Phil has suggested, use Brasso

David

[ekcobeach]

Hi Tony, I had a couple of Pye radios a few months back.I forget the model numbers, but if the knobs on your set are the "round with a slightly concave front and serrated edge" then i know exactly what you mean.Sadly,i don't know the cause but the white bloom was apparent on both radios,but strangely only one knob of each set was affected.The knobs all looked identical in appearance so why it only affected the one is beyond me.It wasnt as if they were both the same knobs either.One was on/off vol and the other was tuning.Anyway,just a bit of useless info. Regards, Colin. <ekcobeach>

[XTC]

Is this down to bleaching of the surface layers of the plastic where sunlight has hit them?

If that's the case, you might be able to polish it out with Brasso, depending on how deep it's gone. The edges of those knobs are knurled, and if that part has gone white, it would be hard to polish off the surface.

If it's grease, I've found it comes off with neat washing up liquid and a scrub with an old toothbrush. Then give then a good rinse in water. A toothbrush is very good for cleaning out crevices such as the knurling.

I suppose the other way of tackling it is to re-stain them. Soaking in black fabric dye might do it. I haven't tried that and it's just a thought.

Pete.

[Robert-UK]

Tony -

If the surface has developed a sort of chalky look and feel, it may be because UV (sunlight) has degraded the plastic surface. Unfortunately this can hapen to a significant depth, so severe polishing probably isn't a good idea - at least without a very careful look first - as you may lose a lot of surface detail. The other possibility is that the surface layer is already gone, and you are seeing the filler in the plastic. This was often wood flour and can look white-ish.

Either way, it may be difficult to rebuild the surface. I'd be gentle with it initially, and Pete's idea of a fabric dye sounds a good start - perhaps followed with a wax polish.

Robert

[maxwell]

Hello there.

I asked this question here some time ago with regard to these black Pye knobs. It seems that they are made from a cellulose material that starts to break down under certain conditions. As long as the knobs are not too badly affected (I have seen some so bad they shrink and distort grotesquely!) you can restore the shine with a small amount of nail polish remover.

Hope this helps.

Max.

[Nickthedentist]

If they're Bakelite, I agree with all that's been said.

More foam cleanser and a smoothish (non-stick) pans scourer will remove grease. If the surface has been degraded by UV light, try a little brown woodstain, followed by some brown shoe polish.

In either case, do try Greygate's Polishing Paste No 6 (BaykoBrite) first - this works wonders on many Bakelite surfaces without having to resort to strong cleaning chemicals or silicones to give a "fake" shine.

Nick.

[rigsby27]

Hello again,

Thank you all for the comments and advice,this weeks house point goes to Max who was spot on.A rub over with nail polish remover (acetone I think) immediately removed the white finish and a small amount of the original 'plastic' but the knobs polished up a treat.

Cheers lads,

Tony.

P.S. sorry for the delay in replying to your help, but we've had a serious family illness.

[ekcopyephilips]

Hi Guys

I have a Pye radio model 19A. It was given to me in a sad state after being stored on a high shelf in an outbuilding and forgoton about for 30 years.

After lovingly stripping, de-woodworming and re laquering the cabinet. Changing nasty waxy caps on the tone control and re-forming the main HT cap, i switched it on.....................nothing.

Ive since discovered that the speech coil output transformer primary seems to be open circuit . It should be about 415Ohms acording to the trader sheet.

Does anyone know of an alternative transformer available today that i could fit, or does anyone have an old one that works that they are willing to sell.

Also why would the winding go O/C ? Im guessing a component short somewhere ? hence too much current draw across the winding.

Any help will be welcomed, im just pied off that i didnt spot this earlier.

Thanks Guys

Mike

[yestertech]

Hi Mike,
Commiserations ! It's infuriating to get the cosmetics all sorted and then to switch on a be greeted with silence - It's probably a combination of damp and possibly a faulty cathode biasing resistor which has led to its demise. As this is 'short' superhet, then for once there should have been no issue with the coupling cap. to the grid of the EBL31 leaking and putting a strain on all the power components for years !
Alas, this OP TXF has a tertiary winding from which the rather complex switched/feedback tone control is derived. SO not a straightforward replacement exactly ! One from a Philips set ( ie 170A ) may suffice. Or anything using an EBL31 at a pinch. I'm off to have a rummage..... Andy

[ekcopyephilips]

Hi Everyone

Well here is the Pye 19A all finished

Thanks to Ed for re-winding the output transformer.

Ive not touched the alignment yet, maybe when i have a brave head on ill have a tweak.

Has anyone noticed bakerlite knobs 'melting' before ? or are these another material, and why have three apeared to have melted and the volume knob is perfectly ok ?

[Nickthedentist]

That's very odd!

I had a very similar Pye 18A (I think) which is now with Paul Sherwin (unless he's got rid of it).

The Bakelite (?) knobs were brittle and at least one was un-usable, but they did NOT go like this! I wonder what's going on here.

Nick.

[PWH]

I have one of these and the knobs responded very strangely to cleaning They went gooey so I think maybe they are not bakelite. I still have them I think, not pristine but better than the ones in your photo PM me if you want them