Most tube radio repairs at Rain City Audio are full overhauls, but occasionally there’s something that’s just in for minor maintenance, like this Admiral AM 488 from 1937. This radio was fully restored in exacting detail both electrically and cosmetically by a gentleman several years ago who has since retired. This radio served faithfully in its new home in Spokane, WA for many years but a few problems recently came up which prompted its trip across the pass and into Seattle for some work.
This radio came with two problems: first was that the volume was very loud and the control no longer responded; second was that the tuning belt had snapped and could no longer adjust the station.
The volume control issues was very easy to sort out: the pot’s lock nut was loose, allowing the control itself to rotate; this motion ultimately caused the low side of the volume control to break free, causing it to no longer work as a voltage divider and making the volume grow much louder. Simply re-soldering that connection and tightening it down was all it took to fix. Then, it was on to a more challenging problem, the belt.
Dial strings are more common than belts and are, in my opinion, a bit more challenging to replace. Not physically speaking, but because they weren’t really made with the understanding that belts break in mind, and thus you’re left to figure out how to wrangle the mechanism to get a closed belt around all the necessary pulleys. A string, in contrast, is usually threaded and joined as the last step. In this case, the first task was to remove the retaining ring and celluloid dial scale, exposing the bulbs (one of which was burnt out, and was replaced) and the gearing. This radio especially was challenging because it uses a two-speed, two-hand reduction gear system for the dial scale.
Removing one screw let the top pulley loose, allowing you to remove the gear and thread the belt in from the top.
Next was the lower half. The belt wraps around two guides, then to the lower string pulley. By loosening the lock-nuts and pushing the shaft inward, a gap opened up between the front plate allowing the belt to be slipped over the lower pulley.
Now, just to re-install the scale and pointers, then re-align the dial with the tuning capacitor.
This radio had developed some hum, too. I replaced the electrolytic capacitors in the power supply for good measure, which significantly improved the hum and improved the richness of the tone as well.
That’s it for this radio! After a trip back across the mountains to Spokane, its owner reported it was as good as new.
Nice job! My Grunow 833 console also uses a drive belt. I bought a drive belt kit from Radio Daze that came with superglue. I was able to make a drive belt without taking the dial assembly apart.