This chassis was brought over to my shop recently. The owner
also brought along the speaker as I had requested.
It looks like a fairly well built radio. At first glance, you'd think it was possibly
a Grunow. But there isn't a bit of identification on the chassis.
The dial is quite attractive, and the telephone dial mechanism seems well built.
The setting procedure for the buttons is ingenious and it took me a few minutes to figure
out how to do it.
If you look closely at the bottom center buttons, you can see a small piece of metal
towards the rear of the button on the upper left. If the button is pushed part way in, this
metal part can be pushed to the right. Then the button can be pushed inward past the normal
stop, and can be rotated to change the dial setting. Once it's dialed in on the station,
the button is released part way out and the metal part is pushed to the left.
Another unusual feature is the voltage selector plug in the rear. It's labeled 177/234 volts.
The tag inside the cabinet also shows the radio can be connected to 117 or 234 volts. Also
unusual is that the radio can be used with 40 to 60 cycles. Perhaps they has export in mind.
Again, no clue to the manufacturer. The dial escutcheon had Fidelitone written on it. Fidelitone
was a major manufacturer of phonograph needles, but as far as I know never made radios. They weren't listed
in the Riders index.
I did have a clue. Years ago, I had a console radio with no identification at all.
It was kind of weird - the owners manual had statements like "For parts, contact the factory",
but no clue where the factory was.
I don't remember now how I figured it out, but I found the set under Gamble-Skogmo. This is a
company no one has ever heard of. But the odds are you've seen one of their radios with someone
else's name on it. They were a pretty strange company - they made a lot of different radios,
then put other people's names on them. A lot of companies like department stores, or companies
that normally didn't
produce radios, but wanted to be able to sell them.
I looked for the model number (A1-MB) under Gamble-Skogmo, but didn't find it. So I had to do
it the hard way - look through all the Gamble-Skogmo schematics in Riders. The easiest way
is to match up the tube complement.
The radio looked like about 1937 or 38, so I started in volume 7. There were 92 pages here, but
many were "catch-up" -
earlier radios that didn't get covered before. Most sets had earlier style tubes.
Volume 8 was a little more promising. And finally I found it on page 8-34. It's a model 762.
The tube layout
diagram was identical to the one inside the cabinet.
Zenith model 5679
This is a unique radio. One of my long term customers brought it in recently. He said he got it
from this old guy named Bruce. I immediately knew who this was - Bruce Gibb, one of the "old-timers" in
the radio club. In fact, he was one of the founding members of PSARA. He's about 91 now, so doesn't
get down into the basement to work on his radios much any more.
Bruce likes Zenith radios above all. In fact, he worked as a salesman in the late 30's, selling
So this has come full circle. I've known Bruce since the 70's, now one of his radios has come back
to me to be rebuilt.
It's a pretty radio. The styling is unusual, especially in the area of the speaker. The grille cloth
wraps around, and the speaker mounts at an angle, facing forward and up. The grille cloth is better
than this photo makes it look.
Here's the unusual feature. It's a farm radio. It's made to run on either 110 VAC or 6 VDC.
I'm guessing it's about a 1940 model. It's pretty deluxe for a farm radio, what with
the pushbuttons and the tone buttons.
The dual voltage input complicates the rebuilding process. The power supply is contained in the box
at the left rear of the chassis. Filter capacitors are on the main chassis, but there are still
some capacitors inside the box that must be replaced. One of them is a buffer capacitor, connecting
between the rectifier plates. It would be suicide to leave it in there.
The "box" must be completely removed from the main chassis. There are seven wires coming out the bottom
of the box into the main chassis, that connect to the terminal strip or tube socket.
Once the wires are all disconnected (remember to make good diagrams!), the box can be
taken loose from the chassis. Once it's off, then the box can be disassembled and the capacitors
Again, I went by the tube complement to find the schematic.
I looked through several Rider's volumes, from 9 through12. Finally I found it in volume 11.
The tube complement is pretty strange.
It has two 6G6's for the outputs. The 6G6 is a low current drain power pentode - the filament current
is only 150ma. But they aren't connected in push-pull - they are connected in parallel. It gets even
stranger - the slide switch on the back panel is a low power drain switch. For maximum battery
life, the switch cuts off the filament to one of the 6G6's so that only one is operating.
All the tubes are low current drain. Instead of a 6X5 rectifier, it uses a 6ZY5 (300 mil filament).
The other tubes are all 150 ma replacements for common tubes - 6T7 instead of 6Q7, 6S7 instead of 6K7,
and 6D8 instead of 6A8.
I'm not sure about the dial lights. The 5654 schematic shows two dial lights and a 13 ohm resistor
in series across the 6 volts. They show the light bulbs as 2.9 volts 170 ma. The Sylvania tube manual
shows type 292A with this rating. Don't think I'll find any at Radio Shack.
The radio has 47's in the sockets. I don't think they'll light very bright with less than 3
volts across their filament.
I guess I could rewire them in parallel. But I'm a little worried about current drain. The radio
has a 6X5, 6Q7, and a 6J8, all normal current drain. With the correct tubes and dial lights, the
current drain would be 1.22 amps. With the tubes presently in the radio, the current drain will be 1.95 amps.
I'm not sure how much reserve capacity the power transformer has. I think I'll feel better with
the correct tubes. They're not expensive - I guess there isn't a big demand for them.
Once the wires are disconnected, the power supply box comes out easily. I took the bottom cover off
and realized I'd underestimated the number of capacitors inside. There are nine. A couple are going
to be hard to get at, but it doesn't make any sense not doing them all - as much trouble as it is to
get at them.
Several of the capacitors are for the vibrator supply. I probably could leave them out, but as long as
I'm goingthis far, I might as well do them all.
There's another funny feature about the radio. On the rear of the chassis, there's an outlet jack that looks
like you should be able to plug in a line cord plug. My first thought was the 3-way portables of the 50's,
where you plugged in the line cord into a receptacle on the chassis when you were running off of
I was wrong. Looking at the schematic, it shows the outlet connecting to the 6 volt line, and it's
labeled "Lamp". Probably, Zenith sold an accessory lamp that could be plugged into the back of the
radio when it was running off a 6-volt battery.
The power supply box is back on the chassis, but i haven't connected the wires yet. There are still
a bunch of capacitors in the main chassis.
The chassis support scheme also came from Bruce. I used 1X3's for the vertical supports and 1X2's
for the horizontal braces. Cost of materials is very low, and it's amazingly effective. It's really nice
to work on a chassis and have it stay steady.
Visible on the back panel of the chassis are the low power drain switch and the socket for the lamp.
The knob selects between 6 volts and 110 volts.