[R-390] Today's Line & Local experiment

[Charles Steinmetz]

Craig wrote:

>Might add at this point, the beast arrived in this condition. R105 was a 5K
>pot when I brought it home and started restoration. So, it has been too loud
>for some time for other owners.

Changing R105 from 2.5k to 5k would not lower the volume, so it is 
unlikely that's why it was done.  But since there is evidence that 
the pots have been monkeyed with, it is worth checking to make sure 
both of them are still log (audio) taper pots, not linear.

According to your data, with an antenna connected, the Amelco is less 
than 5 dB louder than the Motorola (4.5v vs. 2.6v).  We would not 
expect a 5 dB difference to be characterized as unusually loud, or 
"blasting," or "have to turn the RF gain down even with the audio pot 
at zero."  This suggests that the problem is after the volume control 
(i.e., V602/603/604 and associated circuitry).

At this point, I'm inclined to suspect a bad decoupling capacitor, as 
suggested previously by Steve and Drew.  In particular, C603B.  C603 
is a plug-in cap, so you can easily swap in C603 from the other AF 
deck.  That's the first thing I'd check at this point.

Best regards,

Charles