seized core slugs

[pwdrive]

Hello, I have been trying over the past few days to eak out every last microvolt from a CR300...usual problem with the tuning slugs (stuck) I have been freeing them up for alignment (RF,Osc,IF etc) had no problem loosening up the sealing wax but the slots and the formers are full up with the hard red/brown stuff (shellac ?) I filled the top of the formers up with meths and left them for a while to soak, then stuck a soldering iron down there for a few sec. eventually the cores started to turn, is there a better fluid/method that members have had practical experience with.

Lawrence.

[Michaelr]

Hello, I have been trying over the past few days to eak out every last microvolt from a CR300...usual problem with the tuning slugs (stuck) I have been freeing them up for alignment (RF,Osc,IF etc) had no problem loosening up the sealing wax but the slots and the formers are full up with the hard red/brown stuff (shellac ?) I filled the top of the formers up with meths and left them for a while to soak, then stuck a soldering iron down there for a few sec. eventually the cores started to turn, is there a better fluid/method that members have had practical experience with.

Lawrence.

The method you have used is a new one to me and seems very effective well done !

Mike

[TubeType]

Hello Lawrence,
Usually, I try to shy away from using spirits of any kind. They tend to do more harm than good. I prefer your use of heat with a little twist.
My best bet has been to use a small, variable temperature soldering pencil that is fitted with a custom made tip. The tip is fashioned in such a way as to fit the tuning slug's slot precisely. Now, gradually increase the temperature until the wax or varnish begins to melt. Gently engage the tip into the slug's slot and allow the slug to warm up a bit. Carefully rotate the soldering pencil until the slug is free. Patience is a virtue in this venture. Great care must be taken not to crack the slug.
Kind regards,

[pwdrive]

Hello Terry, that's a new one on me but sounds very logical and effective, I have a spare iron and bits it's a 50 watt Antex, it does have a thermostat but not sure how low it will go, I have found that (in the case of varnish) the hardest part is trying to see the original line of the slot on the top of the slug so you can see what to work on or scrape away at, fortunately on this receiver the IF cans come straigh off after undoing the two retaining nuts which enables a better view, this receiver has two seperate IF freqencies in the same can, 95 kc/s for vlf & broadcast band and 570 kc/s for the other six ranges, all the 570 kc/s are at the higher end of the can (chassis topside acsess) and the 95 kc/s are at the bottom of the can (chassis bottomside acsess) I have done all the topside ones no problem and realigned but the bottomside ones are yet to do and will be the worst, I might try your suggestion for those Terry..
Regarding meths spirit, I have never had a problem with it except on some paint finishes, I have always found it pretty inert stuff, is there anything specific to be aware of apart from its flamability.

Lawrence.

Thanks to Mike also.

(addition) If my 50 w is to fierce I might fashon up a length of suitable metal bar that I could pre heat on a gas torch or an electric oven.

[Yorkie]

If shellac is indeed the sealant, then meths is the correct solvent. The 'cement' often used for securing valve bases to the bottles and also to fix top caps on valves consisted of wood flour and shellac. Loose valve bases can be g'lued' back by dribbling shellac sanding sealer round the joint, but if the joint is too slack and the sealer just dribbles through into the base, it can be thickened up by adding some wood flour. It will stick better than other adhesives because the shellac will bond to the original in a way that such things as Araldite or superglue won't. Just use a piece of scrap wood and rub it with 80 grit sandpaper until you have enough 'flour' to mix with the shellac. (Irrelevant to stuck cores of course, but relevant to shellac and meths as a solvent).

[TubeType]

Caveat: Of course, I am assuming your folks over there are as creative as ours over here; when they secure the tuning slug in the coil form. I have seen them use glue, varnish, shellac, paint, wax, fingernail polish, and rubber bands.

With the double slug coils, I usually try to remove the top one first and then the bottom one. Many times, if you are lucky, the bottom slug will have a slot in both of its ends. If so, you can use two tools on it simultaneously, after applying heat.
As a last resort, if the core is still frozen, apply heat to the slug with a firm pressure and push the slug straight out. Slow and steady wins the race.
Kind regards,

[Michaelr]

Caveat: Of course, I am assuming your folks over there are as creative as ours over here; when they secure the tuning slug in the coil form. I have seen them use glue, varnish, shellac, paint, wax, fingernail polish, and rubber bands.

With the double slug coils, I usually try to remove the top one first and then the bottom one. Many times, if you are lucky, the bottom slug will have a slot in both of its ends. If so, you can use two tools on it simultaneously, after applying heat.
As a last resort, if the core is still frozen, apply heat to the slug with a firm pressure and push the slug straight out. Slow and steady wins the race.
Kind regards,

We call them the "phantom fiddlers" over here . Their ingenuity knows no bounds when it comess to the bodge , it is a pity they cannot employ the same talent to getting it right.

Mike

[pwdrive]

I'll drink to that Mike (trouble is I don't drink)
A slot at both ends of the slug always helps as you can always have a go from the other end of the former but in a lot of these early receivers the slugs only have a slot at one end, the worst ones I used to encounter were back in my days of a telly engineer, usually hex cored in a plastic/polystyrene former which had shrunk wrapped themselves round the slug due to the internal heat of the TV, it usually meant breaking them out and carefully cleaning out the former thread, we used to sand the peaks off the new slug thread then apply MS4 to the former and the slug as a lubricant and wind the new slug up and down a couple of times then it was out with the old E2 and some realignment.

Lawrence

[Alistair D]

Does anyone know what threads are on the cores? It might be worth having a tap to help clear any remaining debris from the formers. Alternatively use a screw with the threads filed off on opposite sides.

Al

[pwdrive]

Good point Al, I wouldn't know what threads they are, if it's pre metric I get confused! and I do not have any taps, the same would help on R1155 etc formers.

Lawrence.