[WyTex]

Hi all -

I'm working on a 1940 PT-25. If the humbucking wires are cut, will this block all audio? It's my understanding that a humbucking wire to the coil is designed to eliminate or reduce hum.

The radio was playing but with weak volume. I've re-stuffed the electrolytics and re-capped it. It played very strong for a short time and now nothing. Once while I was checking my work it very briefly came on but then again nothing. I've since noticed the 2 strands are disconnected and wonder if it's my issue.

Thanks,
Paul

[morzh]

If the humbucking wire is cut the audio will stop altogether as it is in series with voice coil.

[Chuck Schwark]

LIke Morzh said, a hum-bucking winding in an EM speaker is in series with the voice coil, so if it's disconnected - no sound from speaker.

However, it can be wired two ways, obviously. The connection one way will decrease the residual hum and the other will increase it.
In or out of phase with the field coil.

Chuck

[WyTex]

I should have realized that it was in series. Still learning here. Is the only repair option to unwind the coil and determine where it was cut? Would it be easier to locate a replacement speaker?

Thank you both for your assistance.

[morzh]

You do not need to unwind anything.

1. Worst case a speaker works without it, just more hum.
2. Simply take a piece of regular multi-strand wire, make as many turns around the field coil as there were originally (I think it is very few, ideally as many as there are turns in the voice coil which is never many) and connect it in series with the voice coil.
Determine the polarity by switching the ends and seeing where the hum increases or decreases.

[codefox1]

Get it wrong and you will do a humdinger, just so you know.

[WyTex]

Do I need to determine the exact number of turns? How many is very few, less than 10? I'm bypassing the original connection correct?

Given my experience, I'll likely do it wrong initially. In my day a humdinger meant I could get zapped good. But I think you're meaning the hum will be so obvious that I'll have to reverse the polarity?

[morzh]

Paul

Ideally you need exact same number of turns as there are in your voice coil. As then the hum current in one will be the exact opposite of the other and they will cancel.

Unless someone knows for sure: you could possibly make a 5-turn coil with long leads, determine the right polarity (by swapping ends) and then by adding or subtracting turns see where the optimum value is.

[morzh]

http://www.ebay.com/itm/Vintage-Philco-4...46246d3dd0


I think this is your speaker.
Not cheap, with shipping.

[WyTex]

I'll have to confirm with the schematic but I think you're right. That speaker price is what I paid for the radio itself. But the radio is to be a gift for my father-in-law so I'm searching for a solution.

Thanks very for your help.
Paul