My current main project, refurbishing my Stromberg-Carlson 520-PG radio (which has been a fair amount of fun so far) is nearing completion. I’ve just completed an IF alignment, which greatly improved the sound quality and volume and general performance.
Radios contained tuned circuits, and like any tuned circuit it can drift over time and become un-tuned. Poorly aligned tuned circuits will result in all kinds of problems – stations showing up at the wrong place on the dial, low volume, distortion, and poor reception. Superhetrodyne receivers, the modern type made popular in the early 1930s and still in use today, convert the incoming radio signals from their radio frequency (RF) level, down to an intermediate frequency (IF). By injecting a signal at the same frequency as the IF and adjusting the fine tuning on the IF transformers, you can measure the changes in output using a meter or even by ear – the volume change is very obvious.
The radio is ready to reinstall:
The last steps are to clean up the cabinet a bit, and repair the grill cloth. I’ve purchased a new grill cloth from Grill Cloth Headquarters (linked on the right sidebar of my blog) and have finally dismantled the mounting board. I’ll be using Howard Restor-a-Finish, #0000 steel wool on scratches, rings and marks and a regular finish application pad for the flat surfaces. This particular cabinet is in excellent shape for its age, and the finish needs just a little touch-up to look great again.
If I’m lucky, I’ll be able to send this beautiful piece of history to its new home in only a few more days.
In this photo, the shortwave loop antenna for distance reception, the cabinet with speaker board removed, the original Webster-Chicago 78 rpm drop changer, and the speaker board. The record changer is still functional, in fact – the motor started up and the mechanism clicked when I turned it on, and pressing the action button made the tone arm lift up, move over and set itself down. Quite a surprise!