Рет қаралды 293
The R-390 tuned circuit IF has more pleasing sound than the mechanical filter IF of the R-390A. These are the steps necessary to convert a R-390 IF deck for use in the R-390A, plug and play. Plug P112 of the R-390A shall be plugged-in to the R-390 IF deck at jack J517. There is much commonality here, except for the connections mentioned herein. In general, you will be converting 25V series connections into 6.3V parallel connections for most tubes, and moving the connections of the BFO/PTO/ballast tube series to a different connection point in jack J517. The 6V filament supply shall be provided to the R-390 deck by pin 20 of P112 from the R-390A. You will be utilizing some of the new 6V supply connections more than once. Make sure you can recognize your new wires. I used black wire for the 25V supply, red wire for the 6V supplies, and green wire for new grounds. The first task is to install a B+ dropping resistor to better match the 180V B+ that the R-390 IF deck is expecting. To do this, locate inductor L503 under the IF deck. This will be found snapped into a holder right above pin 2 of J517. Disconnect one end of the coil, and install in series with it (the equivalent of) a 470 ohm 2 watt resistor. This will tame the B+. See first comment below for the rest of the procedure which was too long for this KZbin description box.