"N_Cook" wrote in message
...
For appearance and modern day use in a vintage vehicle.
That is adding an FM IC inside somewhere rather than RF converter plugged
in
aerial socket.
Assuming there is somewhere around the volume control to switch out the AM
and switch in an FM IC o/p audio . How to secrete that switch and a step
through the band switch as channel changer.

You have just described the FM Module exactly! Just one fly in the soup --
these haven't been available for several years.

I do stereo conversions on these radios. Vintage Wireless in England
(mentioned elsewhere in this thread) also does these, hopefully quicker and
for less money than it would cost to ship it to me.

All of these products originated at a place called Antique Automobile Radio
in Palm Harbor, Florida. Dan Schulz, the owner, began as simply a dealer
who repaired old car radios. As replacement vibrators became scarce, he
started making solid state replacements. Then, as customers were asking for
FM, he designed an FM Module that would fit inside the radio. Eventually he
designed a stereo PCB, and the popularity of these soared -- to the point
where only two dealers in the entire world were still asking for FM Modules
(me and one other). They were finally discontinued. Now Dan is making
reproduction radios for certain cars -- radios that look exactly like the
original, but are complete new radios with the AM/FM stereo technology.

The FM Module was a neat little device. It was a tiny PCB with an FM tuner
built onto it. Connections were to the antenna (with a 6.8 uH choke for
separation), to the grid of the converter tube (or to the LO coil for
transistor sets), to +12 volt power, and to the top of the volume control --
and the wire going to the volume control is rerouted to the PCB.

Switching is done by turning the radio off and immediately back on. PCB's
could be set up for FM first, or AM first. In AM mode, relay is off and the
AM audio is connected to the top of the volume control. In FM mode, the
relay is energized, and the FM output is fed to the volume control. FM
tuning is performed with the radio's original tuning knob -- it uses the
radio's LO frequency to tune FM.

This Module was actually quite a performer, and a very likeable product.
The one and only "bug" of sorts was the fact that it could drift, and the
amount of drift varied with the radio model. The radio's LO drift is
usually not enough to notice, but when multiplied for the FM frequencies it
could make a difference. Even so, it still was a nice product.

At one time, about a third of the radios sent to me wanted the FM Module
installed. It was also handy for early Bendix, and early Delco AM/FM radios
with awful FM front ends. If repair of these was difficult or impossible, I
would simply disconnect the FM entirely and install an FM Module to the AM
coil. The only thing customers ever noticed was that their radio performed
better than ever in FM!

The day the FM Modules were discontinued, I discontinued offering service on
car radios. I've since offered service again on radios, but not on AM/FM's.



--
Gary E. Tayman/Tayman Electrical
Collector Car Audio
http://www.taymanelectrical.com