[R-390] growly BFO

[Flowertime01 at wmconnect.com]

Larry,

The BFO, PTO can has a grounding clip on the shaft like the VLF. Either of 
both can give you problems if they get dirty.

If the 12BA6 has been in place for a while and just started to hum I would 
suspect the tube has flaked some crud from filament heater to cathode. The 
crud being high resistance and not well connected could be more of a 
capacitance coupling than a resistive coupling.

Ground lug problems are likely in the IF deck in general these days, 50 
years with no maintenance of bonds on those lugs is not bad performance.

The 12BA6's are not mil spec but only commercial grade. Your results may 
very from tube to tube and manufacture.

But I suspect a bad tube or a corroded ground point in the BFO circuit.

Roger AI4NI