Just picked up this 1930 Graybar 770 Console radio. A beautiful original survivor. I had never heard of a Graybar radio before- only Graybar commercial and industrial electrical equipment. Not surprisingly, I could not find any data relevant to a Graybar 770, but after some research I found that it was basically a rebadged Radiola 82!
Customer decided to have the electronics repaired after enjoying it muted in their home for many years. These radios are extremely primitive by today’s standards, but highly sophisticated in their own unique way– in any time period.
Something that’s very interesting about these early radio chassis is the way in which the manufacturers used to create ‘capacitor blocks’ by wrapping several paper capacitor sections together and stuffing them all into a single can. During this period, electrolytic capacitors were also very large compared to what they would be in the following 10 years, and so where you would see electrolytic capacitors in a radio from the late 1930s-on were, during this period, instead all wrapped paper and wax; seldom more than 2-3uF per section. Below I’m showing how I manage to rebuild these old paper capacitor blocks with modern equivalent components.
Capacitor block is separated- on this model there were metallic ‘fingers’ bent over to hold the two halves of the steel casing together. After bending them out of the way, the two halves slid apart.
Each of the capacitor sections has a steel band exiting one side which are each soldered to an individual wire terminal. I sever the band to isolate the paper capacitor from the terminal, and leave the original paper block in place. As you will see, the modern replacements for each of the sections are going to be small enough to fit on this end.
Links to capacitor completely severed.
Here is a shot of the schematic print for this radio showing the values of the different sections and to which terminal they are wired, and another shot showing the new capacitors wired per the diagram.
Capacitor block assembled! I like to leave as much of a radio intact as possible. If this radio is re-restored 80 years from now, someone during that time period will be able to see how filter capacitors were constructed 160 years ago, which is something that would be missed if it was removed and discarded. I don’t usually take this kind of care on many of the pieces that come through the shop, as much of what I restore is/was mass produced. I think of this as a ‘first of its kind’ and worthy of preserving the smaller points such as these as examples of the way engineering used to be done.
Another capacitor block, with what the schematic indicates as a 745pF and a .025uF (25nF) section.
As you can see, both sections have drifted from age… and are probably leaky. This meter doesn’t check capacitors for leakage under load, but it does give an extremely accurate reading of it’s effective capacity. We show about 560pF on the one (more critical) section, and .03uF (30nF) on the other. Definitely a problem on both sides.
Cleaned up the dusty chassis and touched up the alignment on the radio, which was surprisingly spot on! Plays beautifully.