Advice on a Philco 444 People's set please.

[MurphyNut]

I'm in the process of restoring my Peoples set I have a few questions, but I don't want to overload the thread with too many at a time so just two for the time being.
Firstly; The perspex 'window' that sits in front of the cursor and scale is misty and orange, (see pic) this really obscures the scale and makes the lettering look horribly faint.
I've tried bleach and a cutting compound and neither touch it in the slightest.
Has anyone found a way of making this kind of perspex it clear again?
of course there's the possibility of making a new one as it's not a complicated shape, if anyone has done this I would be interested in how it was done.

The second question: The electrolytic capacitor in my set is 16 + 8 uf can but I see from the service sheet it's rated as a 8 + 8 uf. The can is dated Feb 56 so it's been replaced.
Where these sets modified to take the higher rated capacitor, or do you think this one was just put in as a 'this will do' job?
Thanks for reading.

[Radio Tech]

Hello Clive

I think the best thing to do regarding the Perspex is to obtain a small sheet of polycarbonate material and cut and drill to make a new one, this material is tough and can be sawn, drilled and bent without breaking or splitting.

Depending on the rectifier it will then largely depend on if a higher value can be used for smoothing. Look up the spec for the valve and go from there.

hope this helps

Ken

[julie_m]

It looks small enough for you to be able to cut a replacement from the front of a CD case.

Don't force the drill bit when drilling the holes, or else the plastic might crack.

According to the data I've found on line, the rectifier valve 80 is only good for a 10µF reservoir capacitor. Which way around is your 8+16µF connected? It would work OK with the 8µF as reservoir and the 16µF as smoothing, though this might be sub-optimal for cooling if it means the reservoir capacitor -- which will have the larger ripple current, therefore more self-heating effect -- furthest from the ambient air. Of course, this could be an Old Wives' Tale anyway; after all, if the smoothing capacitor were on the inside, the reservoir capacitor around the outside of it would be warmer than it, and the heat it produced would have nowhere to go. But with the hot-running reservoir surrounded by the cooler-running smoother, there would be a temperature gradient towards the ambient air. I'm not sure it makes a blind bit of difference in practice anyway; there is exactly the same amount of heat going into the can per second so, when thermal equilibrium is reached, the average temperature will be the same either way around.

[Herald1360]

The specs for the 80 or 5Y3 are a bit coy about cap values- several refer to not exceeding the value in the characteristics but don't give it there!

Eventually found a figure of 10uF max with min 10ohm source resistance. So 16uF is pushing it a bit, though likely you'll be OK since the valve is unlikely to be working very hard in a basic radio.

[ms660]

It's transformer fed so probably good to 32uf for the reservoir.

Lawrence.

[MurphyNut]

Originally Posted by julie_m

According to the data I've found on line, the rectifier valve 80 is only good for a 10µF reservoir capacitor. Which way around is your 8+16µF connected? It would work OK with the 8µF as reservoir and the 16µF as smoothing,

I actually removed the can today and had a proper look at it, in fact I read it wrong, it's a 16 + 32 uf, so completely wrong for this set, it looks like a Dac 90a smoothing capacitor.
I'll wire in two modern 8 uf caps as shows in the service sheet, thanks for the info.

Thanks Ken, I found a polycarbonate sheet online for less than a fiver, it's big enough to almost make 3 so if I mess the first one up I have another chance.

[crackle]

Originally Posted by julie_m

It looks small enough for you to be able to cut a replacement from the front of a CD case.

Don't force the drill bit when drilling the holes, or else the plastic might crack.

CD case plastic is terrible for cracking whilst cutting, even if you have been very careful.

Mike

[Tractionist]

All good advice [above] to-date - I've done a couple of these sets, and on each occasion made a new polycarbonate dial screen [fitting this onto the existing locating pins. and then cementing it in place with hot glue].

With regard to the smoothers - don't push the directly heated 80 rectifier - it definitely won't take 32uf! I've always stuck with 8 or 10uf electrolytics and haven't experienced any excessive hum problems etc.

[David G4EBT]

I've use acrylic/polycarbonate sheet extensively over the years for front panels on my home brew projects. From experience, There's little realistic prospect of drilling polycarbonate sheet using ordinary engineering drill bits (sometimes known as 'jobbing bits'). The correct drills to use are 'step drills' sometimes known as 'cone drills'. Typically, they come as a set of three ranging from 2mm to 32mm in 2mm steps. So if for example, you want a 12mm hole, you start at 2mm which drills the pilot hole then just continue a step at a time till you get to 12mm. No dramas, no accidents.

They cut cleanly and quickly with no 'snatching' and as they're high speed steel (rather than carbon steel) they drill other materials such as die-cast and sheet aluminium, and steel. They're intended for use in a pillar drill run at a low speed (150RPM say) - not a hand-held Black & Decker or whatever. They're widely available and set of three can usually be had for under £15.00. EG:

https://www.amazon.co.uk/MINHER-Tita...p+drills&psc=1

I use acrylic secondary glazing sheet sold by DIY stores. Not cheap, but a sheet lasts for many projects. However, just for a one-off there are lots of suppliers of smaller acrylic sheets such as 'The Plastics Shop'. For cutting to size, I use a fine toothed dovetail saw, but a hacksaw is just as good, so long as the sheet is clamped firmly to a benchtop and the hacksaw is held at a shallow angle to the sheet. The edges can be smoothed with wet & dry paper from 120G upwards.

Each hole drilled represents time spent and care taken. It can be very dispiriting if - having drilled lots of holes - one careless mistake writes off the panel at the 'final hurdle' and it's back to square one. The most annoying thing is that you can sense that it's going to happen, but you still press on anyway, as if to make the prediction come true, as it surely will.

I've attached a couple of pics of home brew project front panels, each of which involved drilling several holes of varying sizes - all successfully completed at the first attempt using a step drill.

Hope that helps a bit.

Good luck in your endeavours.

[Tractionist]

Perspex [obtainable from most model shops] is good too .... but quite soft and easily scratched.

Try to remove the existing screen intact, and use it as a template - this will permit you to accurately make the centre tuning cap spindle/shaft hole .... and in particular, the tiny location pin holes too.

P.S. I recommend installing secondary under-chassis fusing within these sets - because an 80 rectifier short could well take-out the mains and OP TX's + the energised speaker choke etc. etc.

[MurphyNut]

Thanks David, a very comprehensive post on how to do it properly, I've just ordered a set of 'cone drills' for this project.

[G6Tanuki]

Old WWII-and-earlier scale-windows do have a tendency to distort and yellow; I don't know what plastic they used but I've seen several R1155s where the scale-window has distorted and yellowed to the point where you really can't see what's behind it.

In the past I've used cheap polycarbonate sheet [available from places like B&Q where it's sold for secondary glazing] to make-up a new window. The only problem is that if you want to use your old yellowed/distorted window as a template, when you unbolt it from its current installation it may distort/expand in inconvenient ways - if you then use it to cut out a new window you may find you've cut to the distorted rendition of the original and your new one doesn't fit!

The big issue - as mentioned upthread - is that this stuff's brittle and an aggressive drill can 'bite' too hard and cause the plastic to shatter. My solution to this is to use a heated meat-skewer or similar to make holes rather than a drill. A hot skewer will melt its way through quickly, pushing up a 'ramp' of molten plastic either side of the hole. Once it's cooled you can use a scalpel to slice away the excess without fear of causing cracks.

[Boater Sam]

I recently restored a Cossor 464 which has a celluloid window which is not flat, is shaped and they shrink. So much so that they fall out, having no fixings to the cabinet, of the hole that they sit in.

And go terribly brown which is impossible to remove.

I replaced it with a panel cut from the side of a shampoo bottle and stuck it in with hot melt. The plastic is flexible enough to enable some shaping, progressively glueing around the edge.

Sam.

[Tractionist]

Pics of a Perspex replacement attached

[MurphyNut]

Many thanks for the advice and I've replicated the perspex panel, a great improvement on the old one.

[Don Henschel]

Great information David and everybody else! I started the restoration of my 444 and this has been on my mind for a while now about the capacitors. The idea of big is better for smoothing but I have known the initial charge cycle increases greatly with larger caps and can kill an 80! Not so bad using solid state rectifiers but valves are a different story. My electrolytic is original consisting of a pair of 8's@450 volts I do believe. All I have are 5's,10's,15's and larger all at 450 volts. I also read if larger is used, the smaller of the two or more should be the reservoir/primary and the larger (if used) after the choke or in this case the speaker coil used as a smoothing choke. I have never heard this set operated as I don't power up before testing/replacing capacitors for good reason. So far ALL of the Bakelite Block and Paper Tubular test bad with the exception of the Mica. As a result I wondered about how much if any hum there will be using a pair of 8uf? I have been digging in the tar and stuffing the paper tubes until I got stalled on the pair of .00011uf as I don't have anything that size! Too big or too small or very small voltage rating in my disk ceramics. Then I thought about a pair of 10uf, a 10/15, a 5/15? As for the dial window mine is actually not overly bad. Slightly yellow with very slight dullness from wiping with a cloth over the years but clear where it is covered by the cabinet. I wondered if they had yellow tint from new or yellowed with age. Also I will have to examine how the window sits in the cabinet. My white back bolted to the tuning capacitor has the dial and window attached all together using thick cotton string, two pieces one on each end as looped through the holes and tied in the back. As a result I could slide the chassis out with everything in place but removed all of these pieces to prevent damage while having the chassis sitting upside down. After hearing horror stories about damage from shorts how large is your under chassis fuse David?

[Chris55000]

Hi!

Most of tbe contempoary articles recommended a small m.e.s. bulb of about 60–100mA rating in series with the centre–tap of the mains transformer h.t. secondary – you can either use this of a 100mA anti–surge fuse.

Chris Williams