Zenith 8H034 Tube Radio

A while back I picked up an old 1940s Zenith radio.  It uses vacuum tubes unlike radios today.  Of course when I found mine it didn’t work and was well worn.  Here’s a pic of it when I bought it.  The wood veneer had been damaged in multiple places and it appeared that the edge had suffered a little water damage.  The wooden “feet” that are supposed to stick out at the bottom had both been broken.  One of the knobs was missing and the other damaged.  The translucent yellow wheels rotate separately from the black knobs.  The knob’s function on the left is on/off and volume.  The wheel on the left adjusts the tone of the radio which seems to just increase the treble slightly.  On the other side, the knob adjusts the tuning frequency and the wheel adjusts the band.

Here’s a close up of the right hand corner.  This radio has three bands: Std Broadcast (AM), FM 100 (today’s FM band), and an older FM band extending from 42-49 Mhz which is no longer in use.  Also in this picture are replacement “feet” I made for the radio out of some red oak.

Here’s a picture of the back showing the hookups for external antennas.  The power cord comes out of the hole on the lower left but had been cut off by someone.  That’s not a bad thing though because the old cords apparently had a good amount of resistance in them resulting in them heating up.  When the coating broke down and the heated up…it could be bad.

The back can be removed after taking out four screws.  After removing four more screws from the bottom the chassis can be removed from the housing.  The top of the chassis is pretty clean.

Here’s a better view of the tubes.  Note that the silver metal can at the far right isn’t a tube.  It contains some capacitors for cleaning up the converted DC electricity.  More on that in a bit.

Underneath the chassis is a little messy though.  Here’s a couple of pictures.  The plastic rectangles and multicolored plastic cylinders are resistors.  They hold up well over time.  The paper cylinders are capacitors and, over time, they tend to dry out and die.  They’re the main source of problems on old radios.  Obviously, there are other bits and pieces but those are the main two.

If you’re lucky, and I was, you can find a schematic available for free online.  Once you have it you can go through and identify everything.  I took a picture of the bottom, printed it out, and labeled it to make replacing things easier.

There’s a good chance all of the capacitors are dead or will be soon once you try to run the radio again.  So, it is best just to replace them all.  One at a time I removed and replaced the old paper capacitors with new “orange drop” capacitors.  If you look around online you can find them from multiple sources for pretty cheap.

Here’s the view after I’d replaced most of the capacitors.  The big one in the middle isn’t hooked up so I left it in there.  I left a few paper ones in there because I didn’t have the right size replacements.  I did remove and test them though.  If you look in the lower right hand corner you’ll see some black cylindrical capacitors.  These are electrolytic capacitors that clean up the converted DC electricity for the radio.  The capacitors that they replace are all crammed into the metal can I noted above.

Here’s a closer view of them.  I’ve taped over the ends to make sure they don’t contact anything.

The top remains pretty much untouched.  I replaced some wire whose coating was coming off.

To repair the case I mixed up a blend of stains to closely match the original color.  Next, I lightly sanded the entire surface except for the areas around the knobs with the script.  I had no way to replace them that would match the original.

Here’s the radio put back together.  I looked around for some replacement knobs but didn’t find any I liked.  One of these days I plan to turn a couple now that I have a lathe.

So, does it work?  Check out the video below.

Update:

I thought I’d add a few more pictures.  Here’s a view of the top of the cabinet showing some of the damage before restoration.

Here’s a view of the inside of the cabinet.  The white pad is asbestos and helps to keep the heat away from the cabinet.  I’d read that you could seal the asbestos up using a clear coat spray paint to make it safer.  I haven’t messed with it other than that. If you do find an old radio be aware that it may contain surprises.

The finned object in the metal housing is the air spaced variable capacitor.  When you turn the dial to tune the radio, some of the plates move while others stay stationary.  This varies the frequency of the signal the radio picks up.

Unlike modern speakers with permanent magnets, my Zenith makes use of an electromagnetic speaker.  This type of speaker creates a magnetic field with electricity for the speaker’s voice coil to interact with.  This means that you cannot simply swap a new speaker in for an old one without some work.

If you are interested in restoring an old radio there a numerous sites online that provide information and a couple of forums such as antiqueradios.com.  One book I found very useful on antique radio workings and repair is “Old Time Radios!  Restoration and Repair” by Joseph J. Carr.  If you have a desire to restore an old radio, give it a try!  Just take you time, do your research, and be mindful of electricity.