[R-390] R390 Audio

[Bob Camp]

Hi

Most of the classic audio from the good old days ran push pull output 
devices. Since the 390 has a single ended output transformer you can't 
implement this kind of output circuit without surgery. The R390 power 
supply also limits you when you want to put a pair of 6L6's in for 
output drive. One other very simple option is to pull the audio off of 
the diode load. Running it into a decent external amp works better than 
just about anything you can fit inside the radio.

None of that is to say that you don't want to do mods to the audio 
deck. Audio is certainly an area where the radios can be improved. The 
only thing to consider is weather you want to go one way or another.

Here's the suggestion - If you are going to do a "chop and cut" type 
mod on the audio deck anyway then think a little about all the things 
you might want to do. Putting in a buffered wide band output from the 
diode load probably can be done with half a dual triode. Doing it while 
you are laying out the work to be done should be a lot easier than 
doing it after the fact.

The net result would be a radio with three audio outputs - not a bad 
feature. You might also pick the buffered audio off after the gain pot. 
This also would be a nice feature.

	Take Care

		Bob Camp
		KB8TQ