Pye MM

[AlanBeckett]

Thank you and good night
Honest Joe, I'm still fuming at my own incompetence, which just demonstrates that my PhD in Hindsight is in splendid condition.
Alan

[AlanBeckett]

I've calmed down slightly. I've no doubt that I can extract the stub of shaft from the knob. If I can free off the rest of the shaft I may be able to make and attach an extension.
Alan

[Retired]

Hi,

I bet you said something like "Oh dear it appears to have broken" Alan; I also bet you are not amused. Is the spindle alloy like the one on the set I repaired was; I didn't even consider trying to repair the spindle because having an engineering lathe like you I thought I would make a better job of the new spindle than PYE had done in the first place.

It will try your patience and take quite a bit of time making a new spindle as the spindle needs to be accurately made for everything to align.

Good luck Alan; gently gets the job done.

Kind regards, Col.

[Retired]

Hi,

Although I've added notes of the repairs I did Alan I'm sure it would be most helpful if you could add work in progress pictures of your repair. Unfortunately I didn't have a digital camera at the time.

Kind regards, Col.

[AlanBeckett]

Col,

I certainly will.
Unfortunately, I suffered a setback yesterday evening. To cut a long story short I went to rescue a friend whose car had broken down and broke my (home made) tow bar, so I had to mend it. It was just the shackle on the end that sheared. There's a lot of load on it and it doesn't last forever, so every now and again I need to make a new one. In days of old I was happy to tow with just a rope, but that was when cars had bumpers, and brakes and steering worked without the engine running. These days I like something good and solid between me and them. Anyway, it's done, and I can get back to the MM.
Anyway, another couple of days soaking in the Plusgas is probably no disadvantage.

Alan

       

[AlanBeckett]

So,
Back to the MM.
The first job was to attempt to extract the stub of shaft from the Wavechange Switch knob.
This proved to be a complete non-event. I have been soaking it in Plusgas for days, so I nipped the end of the shaft gently in the vice and twisted the knob, which slid off with hardly any effort at all. Insert here a short interlude for swearing and a cup of tea. However, examination of the end of the shaft indicates that it's been cracked for some time, so perhaps it wasn't entirely my fault. The 'Volume' knob came off OK, probably because the shaft appears to be made of brass.

   

The next step then was to attempt to 'get at' the rest of the switch. I decided that it was going to be impractical to continue with the interconnecting wiring in place, so I had to document it all and disconnect. Actually some of it is so brittle - rubber insulation - that it will have to be replaced. Just in passing I checked the valve heaters when I took them out for safe storage and they're all OK.
This part of the radio - sorry Wireless - lives in an two compartment enclosure. The ends and the divider are Alloy castings. The Tuning Capacitor - two gang - is supported on the end castings as Col described. You can see the rear adjustable bearing in the middle of the cross in the second picture below.
I generally try to figure out how it was made, because that usually allows the process to be reversed. Logically you would expect that the whole block was assembled, added to the chassis and wired in. I'm sorry to say that it's not obvious to me. So, I'm going to ponder a bit more and talk to Col. Of course he hadn't got a digital camera when he did his - who had? - so I'm going to send him some pictures to jog his memory a bit more.
Finally I did have one small success. I managed to turn the shaft with a pair of pliers. Not very far, but enough to show that it isn't completely siezed. I'm very nervous about damaging the contact fingers so I'm being very careful. I've applied more Plusgas and left it soaking.

Alan

       

[Retired]

Hi,

Well done so far Alan. I would suggest introducing this chassis to your sledge hammer and explaining to it that if it doesn't behave it will be going to landfill.

The adjusting screw and lock nut appear familiar and I believe this adjusts the end float?

I have trouble remembering what I did five minutes ago but pictures will be most welcome Alan and please add them to the forum as this seems to be a common fault on the MM.

Take it very carefully because it's like a house of cards; it's easy to make a mistake or damage something but difficult to put right. Not only take pictures Alan but make plenty of sketches and at all costs avoid ambiguity trusting absolutely nothing to memory. Take note of how the fingers are mounted and their orientation; I think I had to machine a circlip groove into the new spindle and this was a fiddly job as I had my large Colchester Triumph lathe at the time and had to grind a lathe tool to suit the circuit slot; if I'm correct it is important not to cut too deeply whilst adding the slot and the slot has to be in the correct position.

I further think that I was able to machine the flats in the lathe using an end mill in the three jaw and mounting the spindle in such a position on the tool post that I could gain access with a micrometer to ensure just enough material was removed by constantly measuring the remaining thickness and checking against the original. By mounting the spindle in the tool post it needs very careful setting up. Under a decent light the tool post can be adjusted allowing the blank spindle to just "kiss" the end mill as the cross slide is operated. If you have a carriage lock then lock it. You are used to lathe work Alan so it will then be easy enough to limit the cross travel to suit the length of the flat and the tool post can be advanced in say ten thou increments until the correct flat is achieved.

I've done similar work many times so remembering the actual MM spindle is difficult. I can file to a thou (0.001") but using the accuracy of the lathe once set up is quicker but can also be quicker to destroy the spindle.

Once you send pictures of the original spindle I'm sure it will come back to me. Getting the spindle out is another story as you now know Alan and it's like playing around with a meccano set with all the machine screws.

Keep at it Alan; good luck and above all enjoy yourself. Any chance of making a dozen whilst you are set up as I'm sure others will be needing a new spindle?

Kind regards, Col

[AlanBeckett]

Getting the spindle out is another story ...........

That young Col is what's exercising my brain at the moment.
Attached are pictures of the Left and Right sides of the enclosures. Left and Right in this context are as viewed from the 'Control Panel' at the side of the set. The Trader Sheet implies that the panel on the Left can be removed. In the picture you can see the Tuning Capacitor hiding behind the Aerial Trimmer. However, the switch is on the other side. The panel on that side appears to be removable as well, although there'll be a job lot of wires to disconnect. Having gained access to the switch the question then is how to get it out as the shaft passes through a small hole in the centre partition. Do the contact fingers have to be removed in situ, and of course reassembled in situ later?
Come on Col, what do you remember?

Alan

   
  Right1.JPG (Size: 2.73 MB / Downloads: 121)

[Retired]

Hi,

Thanks for the additional pictures Alan.

When I replaced the spindle I believe I did a lot of unnecessary dismantling resulting in the thing falling apart and wondering what did I do that for?

The first picture (LH) in post #67 shows the spindle and there is an alloy strip secured with a single machine screw; I would remove this and also the cover to the right which shows secured by a single machine screw although this might also be secured elsewhere.

Once these are removed it should give a clearer picture of what is involved. Its possible that after I did all the dismantling which took ages involving removing lots of screws and much de-soldering I found that I could remove the fingers first then slide the spindle out saving a heck of a lot of work.

I hope I'm right Alan and can save you falling into the same trap I fell into; it's a very fiddly job but at least you know it can be done.

Once the spindle is out then it needs copying exactly and if you are using brass rod this will slide back in with no trouble. Don't forget to make sketches of how everything is located.

Please remove the alloy strip and cover then have a good look before proceeding because without hindsight the obvious way to go is to start dismantling everything and ending up with lots of loose wires.

Kind regards, Col.

[Yorkie]

This is proving to be a very interesting thread and apart from the cabinet and the spindle, from the pics the rest of the set appears to be in nice, clean, unmolested conditon. I don't suppose you've got to the stage of testing the two most obvious weak links yet Alan - the metal rectifier, which acts as a voltage doubler. If it's duff (as it has every right to be after almost 80 years!), at least a couple of 1N4007s will solve that problem. The other, more ticklish problem, could be if the field coil which both energises the speaker and acts as a mains smoothing choke, is open circuit. Many hundreds (thousands?) of turns of fine wire with a resistance of 2,500 Ohms, which - if overloaded - becomes an expensive HT fuse! You can of course get them re-wound at a price, but hopefully it will be sound. At least the maker's service sheet is very comprehensive, for what is a simple 3-valve TRF, albeit something of a challenge to restore.

It will be interesting, in due course, to see how it performs on air.

Best of luck with the spindle!