EH Holden speaker impedance (Air Chief radio 63-64)

[Leo.G (Leo)]

Diamond Dot MN-C6B




I've been asked to overhaul/resurrect/restore and old (1963-64) Air Chief car radio for a friend of a friend whose recently purchased an immaculate EH Holden.
My first issue is identifying the impedance of the original speaker so as not to blow the output transistor. From what I can find it's 15 Ohm impedance which I can do with an 8 Ohm unit with a resistor in series (yet to do the maths but probably around 14 Ohm will cover it (or 2 x 8Ohm speakers in series) for my testing purposes, that part is easy.
Then figure out why several wires have been cut internally. A circuit diagram would be lovely, probably as rare as a lotto win.
I used to trace/draw them out by hand, my eyes aren't so good now (it's a simple old circuit board compared to modern stuff with minuscule surface mount components).

Some of these systems had speakers with a mounted transformer, would anyone have any idea where I'd find this information?
Radiomuseum has the radio but no specific information.
I know there's members here who restore cars and likely have knowledge and I'd appreciate any information anyone can offer.


Thanks!

[JA]

Hi Leo,

If you have the radio, try looking on the underside as there may be an info label stating the required speaker impedance. I would NOT add a resistor in series with an 8 ohm driver as it's just lost energy. You could series connect two 8 ohm drivers, but what size is the car's speaker? I'm thinking probably somewhere in the 5 to 8 inch range. I would simply look for a suitably sized 16 ohm full range driver. You probably won't find one new, but used should be easy enough.

Is it one or 2 speakers required? Anyway, if it were me I would try to find a NOT INEXPENSIVE and chunky, JBL LE8 full range driver, given that 8 inch is suitable. With only a few watts output, I think I read 8 watts, you'd want a driver with good /high sensitivity.

Best
JA

[sharkbite]

Hi Leo - i did a quick ebay search and found this:
https://www.ebay.com.au/itm/126061550642
cheers,

[Leo.G (Leo)]

Thanks JA!
No labels anywhere, he was told it was in working condition but I've found cut wires inside and am doubting what he was told. Plus the tuners shaft has been changed and doesn't have the slit in the middle, it's a very rough hand filed piece of heaven knows what, likely glued to the original worm shaft for the tuner, I'll fix that with a small grinder to fit the original knobs he purchased elsewhere.


I haven't spoken to the owner of the radio yet, it was given to me to look at by a friend. I am assuming he wants the radio as standard equipment fit and would assume he's going to mount the standard single speaker in the upper dash panel as was original from memory.
My mention of 2 x 8ohm speakers (or resistor) in series was just for my testing purposes so as not to blow output transistor with no load (too many people do this to good stereo equipment), I could have a 15ohm speaker somewhere here in a box of old speakers and valves.


Thank you Sharkbite!
I'll get the owners email address or phone number and pass that link along.