I'm starting a re-cap on this Philco 39-116. First I tested all the tubes. The #80 rectifier is dead. Filaments are open. Then I noticed that two (2) SK3081 diodes are installed with the cathodes soldered to pin 4 of the 80 and the anodes, one soldered to pin 2 and the other soldered to pin 3 of the 80. Is this an attempt to bypass the 80 rectifier?
Pepperoni
Verify that the B+ voltage is within specified limits as the diode voltage drop will be less than through the tube rectifier.
If it's higher, you'll need to calculate and install a dropping resistor.
Thanks guys! I'm just going to put the circuit back into it's original configuration and install a new 80 rectifier. Do away with these diodes.
Thanks,
Pepperoni
The first cap of the rectifier is usually chosen to set a certain B+ voltage. The higher the capacitance, the higher the voltage will be. But this is only due to the high output resistance of rectifier tubes. Semiconductor diodes have very low resistance, so your voltage might go up quite a bit. Hence what Olskuul said about the resistor. Which could be chosen close to that tube's resistance.
Of course I'm having to build a battery supply for the mystery box. I found this info once and now I can't find it again. What pins on this 4 prong male plug in the Mystery Control do the battery leads (+ and - 3 volts, + and - 45 volts) hook up to? I was able to figure out that the "Red" wire is for the plate of the 30 and the green wire is for one leg of the filament. Lost on the other two. Yellow wire and black wire. This 4 prong male plug is the one that plugs directly into the old battery pack.
Pepperoni