Pye MM

[Retired]

Hi,

Thanks Alan; yes it is slowly coming back to me. I knew the adjusting screw was important and now I recall why. I could not get the tuning gang to align perfectly without it rubbing slightly however much I tried adjusting it and it drove me round the bend. I knew where it was rubbing and previously on other sets I've managed to gently bend it slightly to clear but the MM was having none of this and an outer part of one of the vanes snapped off; but at least it no longer rubbed.

Rest assured the spindle can be replaced so gently does it. You will be a lot happier once the spindle is in your hand. Tomorrow is another day.

Kind regards, Col.

[AlanBeckett]

Col,
That's why I'm desperately trying not to disturb the Tuning Capacitor adjustment.
I've had another look and I think the solution really is to remove the panel on the other side. It looks straightforward enough, and I hope the partitions, which are screwed in from the bottom, will be stiff enough not to move.
I'll report tomorrow, I hope.
Alan

[AlanBeckett]

So, 'Once more unto the breach, dear friends, once more;'
After an overnight ponder I decided that the only solution was to remove the Left Panel.
Following on from the previous numbering:-
Step 8 was to remove the 8 Cheese Head screws from the outside of the Panel and one inside. This exposed the whole of the (internal) switch mechanism.
Step 9 was to remove the 4 Cheese Head screws holding the Control Panel to the Chassis. I'd assumed (rashly?) that this ws Bakelite, but in fact it's another die casting. That exposed the Pilot Bulb and the Detent Mechanism.
Step 10 was to remove the two Cheese Head screws holding the bulb holder to the chassis.
Step 11 was to remove the Detent Spring which fully exposes the (broken) end of the shaft.
Step 12, just in passing, was to have a look at the bulbholder, which seems over complicated. The answer is simple; you can't get at it in normal circumstances so it's designed so that it can be rotated - neat.
That's enough for now. I'll press on with more pictures etc shortly.
Alan

                   

[Andrewausfa]

The chassis seems in remarkably good condition. It's fascinating looking at all the parts that make up an early-ish wireless. Having never seen or heard a TRF set working in the flesh, am I right in thinking you'd get a rough signal for a station and then fine tune with that large circular capacitor in the middle photo?

Thanks _ Andrew

[AlanBeckett]

So, to continue:-
Step 13 was to measure the shaft. It's 1/4" as Col said. However, I can't find any evidence of how the shaft is located. I can only think that it's the knob and the detent mechanism, at least in this version.
Step 14 was to photograph the 4 shaft positions - there's no real point Posting them.
Step 15 was to remove the Switch Blocks - I can't think of another name.
Step 16, finally, was to remove the shaft. Anyone of a nervous disposition should stop looking now. It was still very stiff to turn. The bearing surfaces are the front and back plates - there's a clearance hole in the middle one. A gentle tap on the end would move it but only a little. I was very nervous about applying any serious force because I didn't want to damage the partitions, which were only supported at the bottom at this stage. Anyway, I decided in the end that my best bet was to grasp the shaft with a big pair of pliers and tap the pliers. In a way this was 100% successful in that the shaft was extracted with no damage to the partitions. The bad news ius that the shaft is now in 6 pieces as it broke at its weakest points, as Col found. In retrospect I suppose the way to do it would be to make a gadget to push the shaft out of the end plate. Anyway, what's done is done. I don't think the replacement needs to be ultra accurate as there's clearly a lot of (potential) slop in the arrangement. However, Col, if you made a sketch of your shaft when you made the new one it would no disadvantage to have it.
So, I need some material to make a new one. Just like Col I favour Brass. Stainless Steel would be good but it's often a pig to machine. Anyway, Brass is more in keeping with the era.

Alan

       

[AlanBeckett]

Andrew,
Actually the other way round. You'd set the 'Volume' control, which is actually mainly the Reaction Capacitor, to about mid way, find a Station, then trim it up with the Aerial Trimmer, and adjust the volume with the Volume Control.
I expect most of them simply got set on the local or National Station and left there.
I've attached an anotated Circuit Diagram.
Alan

   

[Joe]

What a saga! Glad to hear it's out at last.

- Joe

[AlanBeckett]

Glad to hear it's out at last.

... as the Artmistress said to the Gardener

Late update:-
I've just been down to the garage to shut down - by the way the small heater is keeping it very cosy in there - only to find that the Tuning Capactor is all over the place. It turns out that the front bearing is a 'pip' on the Control Panel which I hadn't noticed, and which of course I've removed.
It should be OK when I put it back as I haven't disturbed the other end.
I also forgot to say that everything else looks OK. I thought I'd got some 1/4" BMS but I can't find it. However, a bit of 6mm through the holes looks OK, and if the worst comes to the worst I've got a 1/4" reamer for the holes.
Alan

   

[Retired]

Hi,

What a disaster Alan; it's a good job you aren't working for the army bomb disposal gang.

I'm sorry but I didn't make any sketches of the spindle as it wasn't needed having the original spindle in my hand to copy. If I had such a sketch I'd have posted it ages ago.

This demonstrates just how weak these spindles really are; they break at the slightest touch hence all my previous warnings. Well it's now finally removed so you have even more fun to look forward to in making a new one. One thing I would add is that I never withdraw shafts or spindles without ensuring the exposed parts are not cleaned first and checked for burrs; it doesn't take long to wrap a bit of abrasive paper around and polish before withdrawing after adding a drop of lubricant. It only takes a small burr to lock everything up solid.

I agree Alan about stainless being difficult to work; this also applies to silver steel as bought as it too is tough stuff. Precision ground mild steel is readily available and cheap enough but like you Alan I thought brass would be more in keeping given the age of the set.

I took great pains whilst making the spindle ensuring it exactly matched the original; the flats took a lot of time to add because I used a micrometer to ensure they were at the the correct depth by constantly measuring the remaining thickness as waste was removed; the flats were also made to exact lengths of the originals.

Drilling holes either clearance or tapping size needs a lot of care as there isn't a lot of material to play with. Adding the square at the spindle end was also entertaining as it is difficult to obtain an exact square and easy to end up with a strange shape.

I was sure that the spindle I made had a circlip groove but as it was so long ago I could be mistaken as I have made a number of spindles over the years; if the groove is not required it saves considerable work in not having to grind a special lathe tool.

One thing is for sure Alan; if ever you need to do another MM you will be experienced and do the job much quicker. Now that it is out have you noticed as I did that a lot of the dismantling was not needed?

Making the spindle for me was straightforward enough just taking a lot of time and it was easy to install. What caused me a great deal of trouble was getting the tuning gang to align and it drove me around the bend; I wondered if the factory used jigs to align the frame members?

Hopefully the hardest part is now over and once the new spindle is made you will make rapid progress.

Good luck Alan my fingers are crossed for you.

Kind regards, Col.

[AlanBeckett]

Col,

Ah well, it was worth asking.
I don't expect it to be too difficult to work out the original dimensions as they're almost certain to be 'sensible'. After all, if you're sitting in front of a Drawing Board with a pencil and a square there's little point in going in for exotic measurements. It will of course be Imperial. Just on that subject I was surprised how close to 1/4" the shaft measured. It doesn't look as though it's been machined anywhere so as you said that's the straight casting.
I've decided on Brass and I've ordered some. As I said earlier I think I can arrange a set up which should take most of the hastle out of the machining. I also think I've got a nice new sharp 1/4" Slot Drill which should suffice. I'm not sure that I've got the right drills and Tap so I'd better check.
So, next step is to make a Drawing.
Watch this space.

Alan