The Stovebolt Site Forums The Shop Area The Electrical Bay The Radio Bench A few questions about original radio wiring.

Installed my original 1949 Chevrolet AM radio in the '49 1/2 ton pickup. I don't want power to the radio from the ignition switch when the ignition is in the off or on position. Is there any problems created hooking the power source to the radio to the ignition on side of the switch? Does the radio need to be turned on for the dial light to work? Have no dial light with the switch turned off. In other words, does the switch have to have power to it for the dial lamp to illuminate? Checked the bulb and it is good. Have power through the line to the lamp fuse holder, but the dial does not light with the switch in the off or one position. Have not yet hooked up the radio power wire as I am trying to decide if I want power with the ignition on, or continuous power operated by the radio on off switch. Suggestions....advice??

Thanks,

Tim

Yes, the off/on switch on the radio controls the dial light too so if you turn the radio off, the dial light goes off. The separate dial light feed is meant to allow you to vary the brightness along with the dash lighting.

For power, the original instructions called for power that was not switched by the ignition.

Truckernix, I found this thread searching for the right place to connect my old tube radio power lead. I think I have the Delco model 986067, and using an ohm meter, I have figured out which wire is the power lead, just need to know the proper place to attach the power lead. Is it ok to connect it to the ignition, or should I be connecting to something else?
Thanks!
mark

attached photos
- a reproduction i made of figure 1 from installation bulletin for 986067 radio showing the A lead fuse holder and the dial light lead
- a photo from ebay of an original A lead fuse holder connector, both halves

the A lead is meant to connect directly at the amp-meter post,
the early radio draws over 6 amps with it's electro-dymanic speaker accounting for half that current, you don't want that on the ignition switch
later it shipped with a permanent magnet speaker, but that's still about 3 and change amps

the dial lead connects on the light switch where the dial lights are connected, the radio comes with both wires long enough to reach these locations
from inside the radio both wires are approximately 26 inches to their respective ends.
hope that helps
-s

i almost forgot, the radio ground is "poorly to the dash"
it's silly to realize all the troubles the designers went through to reduce noise and interference with this delicate radio design
and then just let it have a random ground path through paint and rust

i recommend adding an explicit ground wire from inside the radio on the main chassis on the power transformer side, bring that out and screw it down on the fire wall
this will ensure the antenna ground plane (aka the cab) is reasonably well connected to the radio guts
you want to minimize any current flow on the antenna coax outer shell, connecting the guts to the firewall will help a lot with this goal

if you were to float the radio electrically while it's turned on, it would operate, and 100% of the ground current would flow down the antenna coax shield to where the antenna mounts on the cab
if your antenna coax shield is not tied to the cab at the antenna base you won't get as good a signal and your radio will be susceptible to RF noise
make sure that antenna shield ohms out low to ground before plugging it into the radio
-s

Thanks! This is very helpful. Does it matter what side of the ammeter that i connect to?
I wondered about the ground, and it makes sense to go ahead and make a direct ground as you suggest. Another dumb question, but if it becomes necessary to remove the radio, do the radio knobs just pull off?
Thanks for the quick reply!
Mark

You want to connect the radio feed to the load side of the ammeter, not the battery side.

hi Mark,
the radio connects to the discharge post of the amp-meter so that it indicates the radio current
example, with engine off, radio on, you should see the amp-meter needle showing discharge to let you know your battery is draining
photo attached from installation guide

the original radio knobs have a set screw, but as old as the radio is, the replacement knobs from even way back in the day were press fit
so by now, you might have either kind of knob
turn the knob and look for a set screw,
if no set screw, it pulls off
i took some photos of original knobs i have on hand, i am missing an original dummy spacer that goes behind the tuning knob
-stan

Awesome! Thanks Stan. I feel like I am on my way to finding out if this thing will make some noise or some music soon... Thanks so much.
mark

I think this thread just answered my most pressing question prior to bench testing the vintage Chevy radio I received in a box with my nicely restored 1948 one ton. There is only one wire coming from the inside of the radio,and I assumed that was power since it had half a fuse fixture attached to the end of it. Meanwhile I have been looking for and trying to understand why there was no ground wire.

So, the original intent, which I just saw in Stan's reply was; grounding via just bolting to the dash frame, am I reading that correctly? Ensuring a more reliable ground seems good advice, so anywhere on the radio frame next to the transformer should work? I have not had a lot of experience electrical bench testing something like this radio so any advice would be helpful, e.g. just hook it to the 6 volt battery in the truck (with an in-line fuse of course) or??

The exterior of the radio looks great! Inside, not so much, very dirty, appears some capacitors have been changed, lots of lumpy, cold looking soldering, and a Radio Shack speaker. Still worth a bench test first I think. I have no idea how long this radio has been setting in this box. The PO who had this truck restored and included in his collection of really nice restored vehicles passed away before having it installed, so it was just included when the family put the truck up for sale.
Dale

That is correct for ground
The main body of the radio is the intended return

adding a dedicated wire from the inside chassis on transformer side would not hurt.

There should also be a dedicated dial lamp wire to connect to the back of the light switch
The dial lamp will dim with the instrument lights
The dial lamp wire is also switched inside the radio so when the radio is off the dial lamp is off as well
-s

Thanks, there is no dial lamp wire, but I can see the dial lamp wire now, inside the radio, soldered or attached to what appears to be the power source wire. No other extension. Not sure yet how to correct that but will bench test first to see if anything works, then get back to it. Thanks again. d

The design of the radio relied on the chassis being grounded to the case. The tuning assembly is grounded to the case by a soldered braided conductor.

With regards to testing you can power it up with the truck battery through a fuse, (10 A or so). You can use a piece of hookup wire, say six or eight feet long for an antenna. Just bare a bit of the end, maybe double it back if it is too thin and insert it in the middle hole of the antenna socket. Some radios with the electronic vibrator do better with the higher charging voltage, around 7.4 volts. If you are in a steel clad building, you might want to test it outside.

Thanks everybody, and thanks Truckernix for the antenna tip. Bench tested, and it works like a charm! Listened to music for few minutes and got immediately ready to install, just have to order an antenna since the truck apparently has never had one. Who needed a radio driving through grain fields in the old days, but now it will be a nice add to the old truck knowing it works. Nice looking too! Dale

That is good news. I forgot to mention about the dial light wire or feed. Originally the radio would have had a dual off/on switch that switched the main power and the dial light on separate leads. It was common for one of the switch contacts to wear out and stop functioning. The cure for that is to connect both to the working set of contacts. The combined volume, tone switch and power switch used on the truck radio are very hard to find for replacement. Almost all the other radios used a continuous tone control.