GEC - Knobs

[DonaldStott]

I have a GEC BC5050 on the bench at the moment but have only been able to remove two of the four knobs. For the avoidance of doubt these are pull off knobs and there are no grub screws.

This is the first time that my trusty PlusGas has let me down and I’ve tried most of the techniques mentioned on this Forum so no need to revisit those.

I’m considering using my hot air rework station to gently heat the shafts but am obviously concerned about inflicting damage on the set or the knobs themselves. The knobs in question are on the wave change switch and the tuner dial cord!

Any advice on what would be a safe temperature to use? I’m particularly concerned about overheating the dial cord!

[Nickthedentist]

Mmm, the knobs look relatively tough, and they're surrounded by wood rather than glass or plastic.

I presume you're tried two levers diametrically opposite each other, with a thin bit of metal to protect the woodwork?

These work really well, usually called "tack lifters": https://www.wilko.com/en-uk/wilko-sc...00mm/p/0286615

And the cheap cabinet scrapers you can get in a multipack in Poundshop etc. are great for cabinet protection.

I don't know how the chassis is fixed, but it sometimes helps if you loosen it, slide it forwards for better access, then secure it again so that the levers have something solid to pull against.

[DonaldStott]

Thanks Nick - my tack lifter was used to successfully remove two of the knobs but the other two won’t budge!

I’ll have a closer look at how the chassis is fixed to see if there is any scope for movement.

[The Philpott]

Is your freezer big enough? I think heating could cause relative expansion to crack them, but bagging it up and freezing would cause the shaft to shrink back..? (At least enough to allow penetrant in)
Dave

[DonaldStott]

Thanks Dave but unfortunately I only have a domestic three drawer freezer so no room for a GEC radio cabinet.

You’ve given me an idea though and I could try a freeze spray of some sort?

[Nickthedentist]

Or drill a neat, small diameter (2mm?) hole in the centre of the front of the stuck knob so that you can drip some PlusGas on the other end of the shaft. If you're successful, the hole could be quite easily filled with coloured epoxy or similar, and the knob re-used.

[snowman_al]

I would stick with the two pieces of cord method. (One piece either side of the shaft, twist them together and tie to form a loop at the front that you can pull on.) You do not prize on the case then and if you are careful you can put a lever through the loop and apply much more pressure. As the knobs do not have a thin flange, you can be pretty brutal...
I assume they are 'D' shaped shafts?

[Nickthedentist]

I always worry about what's on the other end of the shafts when I use force.

I was working on a rusty Hacker the other day, and the knob came off with the entire shaft. This wasn't as unfortunate as it sounds though, as I could then remove the knob from the shaft with the aid of a bench vice, and the shaft popped back into the remains of the pot without any drama.

Horologists face a similar dilemma with clock hands. Although pullers exist, they rarely seem to fit whatever clock I've got on the bench.

There have been suggestions about pullers for knobs on the forum from time to time, e.g. https://www.vintage-radio.net/forum/...d.php?t=116962

[snowman_al]

You are of course correct pulling may result in damage to the component related to the shaft...
Unfortunately all the methods need a pull to get the knob off and some sense of force need vs pending damage is assumed.

Maybe possible to drill your hole on the side of the knob rather than the centre so it would not be obvious ?

Maybe a push on before a pull off may break the adhesion?

[David G4EBT]

Originally Posted by Nickthedentist

There have been suggestions about pullers for knobs on the forum from time to time, e.g. https://www.vintage-radio.net/forum/...d.php?t=116962

The DIY one at post #6 of that thread by 'Surrey Nick' is an effective, easy to make, low-cost option.

As I've passed through life, one of the harsh lessons I've learnt is to occasionally temper my enthusiasm with discretion.

When screwdrivers, tack-lifters and the like are used, you 'ride at your own risk' and it rarely ends well.

Stage 2 is a forlorn post in the 'wanted' section for replacement 'unobtanium' knobs.

Good luck with it.

[radiomobile]

A method I have used, in desperation where spare knobs are available, is to "destroy" the knobs off by crunching them in a bench vice. Sounds brutal and help is needed to support/manouvre the radio but it does avoid damage to the cabinet or fascia ( I used to deal mainly with car radios ) and importantly to the switch or whatever is on the other end of the shaft inside the radio. A piece of hardboard with a 7mm slot cut in it slid between the case and knob avoids damage. Probably not appropriate in this case if replacement knobs are not available.

[stevehertz]

I posted about my knob puller some years back. Read the thread, they are expensive to buy if you buy the pukka stewmac one, but you can make your own: https://www.vintage-radio.net/forum/...d.php?t=116962

[electrogram]

I don't know if this is possible in your case but on at least one occasion rather than sacrificing the knob I cut through the spindle, from the inside of the cabinet, with a hacksaw blade, awkward and time consuming, and joined the two bits together with a spindle coupler. In some cases it might be possible, with chassis bolts removed, to push the chassis far enough forward to cut through spindles from the outside, leaving a long enough length of spindle protruding from the knob to join with a coupler. Although I had a spindle coupler to hand I did look on line for some to see what was out there, only to find they were unobtainable, but eventually discovered that [I]shaft[I] couplers were readily available.

[DonaldStott]

Originally Posted by David G4EBT

As I've passed through life, one of the harsh lessons I've learnt is to occasionally temper my enthusiasm with discretion.

When screwdrivers, tack-lifters and the like are used, you 'ride at your own risk' and it rarely ends well.

Thanks David - you know me too well!

In Post #2 above Nick advised that I loosen the chassis and slide it forwards for better access - this was duly done which meant that the knobs and shafts were well clear of the cabinet. Why didn't I try this earlier?



Another squirt of PlusGas but better aimed this time and left overnight to do its work.

Positioned a small sheet of 16 SWG aluminium against the cabinet to avoid damage and it was possible to get in behind the knobs with the tack lifter and lever them off - still a bit of a struggle and quite exciting (!) when they went flying across the room!



Not for the faint hearted and certainly not recommended - I can only say that I was lucky this time?

Thanks to everyone for their valuable and helpful suggestions which now comprise a useful list of techniques to try in the future should we encounter a similar problem.


POSTSCRIPT

So all four knobs removed, chassis out of the cabinet and we have a dead short across the live and neutral wires of the mains flex!!!

See here: - https://www.vintage-radio.net/forum/...4&postcount=53

It's been 'got at' so here we go again ...

[ms660]

My old trick was to lock the shaft then "twist" the knob both ways to break the stiction then remove.

Lawrence.

[snowman_al]

Phew!

[Nickthedentist]

Well done. And useful trick, Lawrence.

[The Philpott]

Glad this worked- it's sometimes possible to get a more evenly spread pull than with a tack lifter- by using a knackered wood chisel which has been modified by having a notch cut in the end with a grinder.
Dave

[high_vacuum_house]

One method I have used in the past for pulling stubborn knobs off is to slide thick cardboard between the rear of the knob and the cabinet to act as a cushion, then to remove all of the chassis bolts. You can then try and pull the chassis out of the rear of the cabinet. You can grab the chassis easier than the knob and exert more force. It is then much easier to give a non leverage type force onto the knob which minimises uneven force and the chance of the knob head snapping off. It also prevents accidental slipping with an implement and scratching the front of the cabinet.
Christopher Capener

[radiograham]

Hi,i once had this problem with a Decca 1000 projection tv,couldnt get the knobs off working from the front luckily i thought the spindle couplers inside the set would come apart more easily,ha,took 2 or 3days to get these off! it was one of the worst jobs ever. Graham.