Allwave 15 tar caps? Necessary to change?

[Paul Kasindorf]

I have seen various posts on different sites mentioning the these big tar boxes. It seems, from what others more knowledgeable than me say, there is more going on in them than capacitance. Is it totally necessary to change these?

I have restored mostly 1920s simple sets, and I don’t want to mess up something so valuable and historically important in trying to bring it to life.

Thanks for your input.

Paul

[Kent King]

So the metal encased capacitor blocks in the IF circuit, typically mounted on the rear apron, do contain a combined inductance and capacitor. They are used in the cathode circuit, running at much lower voltages then the usual B+ levels. That said, I do typically replace all wax and tar caps in my restoration work. The AW15 is usually a hybrid for me though: Those caps that have combined inductors are left alone initially. Once I do my other work, I will gradually power up the set on a Variac and see how well it works. If it plays and aligns to spec without replacing those units, then I leave them alone. If the set doesn't work or can't be aligned, then I will replace one or more.

If you get to that stage, I soften the tar in a small toaster oven I bought on the cheap at Goodwill. I try to recover the inductance, and then rebuild the unit with a new and and the original coil. I prefer to reseal these with beeswax rather than tar. I've had success both ways with AW15 sets. You can also get a modern inductor to install in the can. So you don't have to worry too much about a restoration going wrong - some efforts require more work than others.

If you have other questions, keep asking here, we're always glad to help.

Kent

[Paul Kasindorf]

Thank you so much for the suggestions and moreover the education. I’ll probably start digging in to it in a couple of weeks. I really appreciate the offer of help… I will surely need it.

[mike hadley]

Hi Paul,

Here is a picture of one of the bathtub caps with the choke in, this is from my allwave fifteen,

once removed from the chassis the back will need to be removed from the bathtub as its soldered on.

Looking from the back of the bathtub, the cap is the long cylinder to the left and the choke to the right, the box is filled with pitch.

The capacitor choke junction is marked with a red dot of paint next to the lug, the other end of the cap is internally connected to the case.

Be careful of the choke wires as they are quite fine easily damaged, but as Kent suggested they can be replaced.

A modern axial polypropylene cap (one of the yellow ones) will be a nice fit as they are about the same size as the original paper

Mike