CVRS Member

I spent a really long time studying the schematic to try to understand why the heater voltage is spiking and killing the panel light and 35W4. I found a Description and rating of a 35W4 (below) and don’t understand how the line voltage is transformed into 35 volts for the heater circuit. I don’t see a transformer in the circuit so is it resisters? All test O.K. or are replaced. I can only assume I’m not understanding something fundamental about this circuit as my instinct is to put a meter on pins 3 and 4 of the 35W4 and take a reading. I have looked at the base of all the tube pin sockets and in general for wiring that may have been disturbed when I worked on it. I could find nothing wrong. I have read “The fundamentals of radio”, but how much I retained in my 63 year old brain is questionable.


Also found this

“As a cost reduction measure, especially in high-volume consumer receivers, all the tube heaters could be connected in series across the AC supply using heaters requiring the same current and with a similar warm-up time. In one such design, a tap on the tube heater string supplied the 6 volts needed for the dial light. By deriving the high voltage from a half-wave rectifier directly connected to the AC mains, the heavy and costly power transformer was eliminated. This also allowed such receivers to operate on direct current, a so-called AC/DC receiver design. Many different US consumer AM radio manufacturers of the era used a virtually identical circuit, given the nickname All American Five.”

Lastly, to make testing the circuit easier, I thought about busting open one of the burnt out 34W4’s and converting it into a tool to test the circuit by soldering on test wires to the pin base of the tube in order to check the circuit easier with a meter and insuring the pin socket doesn’t get damaged from probing. I can’t always get underneath every tube to test it there. I made one , here’s a pic…