February 23, 2013 at 1:52 pm #3879Ed KrausharCVRS Member
I was given this B power supply when I purchased two 1020’s radios this month. It is made by King Electric Manufacturing Company in Buffalo New York. It will go well with my King radios.
I opened it up with the intention of restoring it and found that it had already been “restored”. In its past someone had partly rewired it and sealed the wires and all connections with some type of liquid rubber. Very stretchy and very hard to remove. The problem was that they did all that work and did not change the filter capacitors. This ment using a sharp utility knife to remove the rubber and wiring to get into the can containing the filter block. There are four cans, one is the power transformer, two are chokes and the fourth is the capacitor block.
I had this typical schematic from an early version of the NRI Radio-Trician Service Manual to work with.
My unit has identical wiring except for the cap values. My cap block inside the can had values marked on the block and were 2, 4, 6, 1 & 1 mfd going across the schematic. I made up a block with 2.2, 4.7, 22, 1 & 1. I used a large final filter cap to reduce hum.
The next problem was the BH rectifier tube. It was missing and I did not have a good one. To get this going I made up an adapter to use a 0Z4 gas rectifier. The adapter was an octal tube socket in an empty 4 pin tube base. Connections were octal socket 5 to tube base 1, 3 to 4 and 8 to 2. When you substitute these tubes understand that the BH drops 90 volts and the 0Z4 only 24 volts. This will give you higher output voltages.
The King supply has rheostats to adjust the detector and amp voltages but nothing for the power tube voltage. When tested I was getting a power B+ of 330 volts DC with the other voltages correspondingly high. Even with a BH tube it would be too high. Reducing the input AC is not a good option as the gas rectifiers need a high voltage to start up. I played with voltage dividers a bit but I was getting pretty hot resistors and still a fairly high output voltage when no load was connected then dropping down when loaded depending on the load. Ideally I wanted somewhere over 130 volts DC going into the supply control panel so that radios with various tube numbers could be used.
In this case I decided to stray from my preference of no major changes and used the extra space in the back of the supply case to install a series resistor and a 0D3 cold cathode voltage regulator tube. This tube regulates the power B+ to 150 volts and allowing the rheostats to adjust the detector and amp B voltages as required by the radio.
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