allwave fifteen voice coil

[mike hadley]

hi,

can anyone help with the voice coil impedance on an allwave fifteen,

the cone has been removed but the spider and a badly damaged voice coil is still there,

the wire gauge of the coil is about 30 awg, and there are 64 turns, feeding this into an online calculator I get 3.4 ohms.

is this correct?

i was expecting somewhere around 8 ohms or higher.

the speaker is a cast basket pedestal type.

many thanks

mike

[Norman S Braithwaite]

At what frequency did you calculate the impedance?  I am not sure but I think that 1000-hz is the frequency at which voice coil impedance is usually specified.

Norman

[mike hadley]

Hi Norman

Unfortunately the only measurement I can give is dc resistance, the coil is in such a state, several turns missing, only the shadow left in the old adhesive,

I have been down the rewind route before and usually an 8 ohm coil won't be too far off on dc,

I have read before about odd impedance readings but they are usually higher.

thanks

mike

[David C. Poland]

Mike - I get 5.1 ohms resistance on a digital meter.  So 6 - 7 or so ohms impedance.

I have an AW-15 speaker (the correct 12 inch Jensen made pedestal) that is a bit rough but the voice coil is intact. I lifted on one of wires from output transformer to measure the voice coil resistance,  

[mike hadley]

Hi David,
Thanks for checking your speaker, I think that the speaker I have is the original to the radio.
Looks like a Jensen pedestal, the coil has two layers of 32 turns and I will get 3.4 ohms,
rough guide is to multiply this by 1.3, this will give me an impedance of 4.4 ohms, so not too far off,
Worried about reflected impedance in the output transformer when I get the speaker done.
Thanks again
Mike

[David C. Poland]

Did not know VC was 2 layers of wire. Assume you got an accurate gage of the old wire.

I have had my hands on several of those Jensens for the AW-12 and AW-15.

So far, every AW-12 speaker had good field coils. 

Half of the AW-15 speakers had an open field winding. Bias winding OK, B+ open.

Hope yours are OK.

[mike hadley]

Yes both coils are ok as a previous owner has put a 12 inch dynamic speaker in the cabinet,
And have left the coils as part of the power supply circuit, radio did sort of work up until one winding developed a short
A few days ago,
So transformer is now being rewound,
Also taking the opportunity to re cap as last owner has missed a few.

[mike hadley]

Just posted a couple of images of old
Voice coil

[mike hadley]

And another