[R-390] RF Module Adjustable Slug Seperated from Adjusting Screw

[Drew P.]

Paul wrote:

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"This particular R390 appears to be a low mileage Collins original, still has its original green gear!. It had a short on the audio pre-amp plate circuit. To get it going, I swapped the audio module and the set started working. Needed a ballast tube (I'll replace with 12BA6's for PTO/BFO and short the ballast tube socket) and had 3 weak tubes also. Has anyone tried keeping the 6BA6 PTO/BFO tubes intact and used a diode to replace the ballast tube ?"

The radio will work with just a diode to replace the ballast tube, but the voltage to the PTO and BFO tube heaters will be too high - about 9 volts RMS on each of the two heaters. If you place a 20 ohm resistor in series with the diode, then all will be copacetic in Heatersville.

Drew