[R-390] RF Gain control

[dog]

Thanks Roger, I sort of expected that about the RF pot, having taken it 
apart and carefully inspected them. Just wanted to check. Yeah, I sort 
of know they were mostly just sitting there listening to RTTY where I 
saw them. I never got to a Morse intercept station, so I don't know how 
the CW guys used them. They probably rode the gain pot in MGC? Maybe not 
being on a typewriter.

I've done the S/N test with 30% AM modulation and both seem to be below 
1uV, even to the balanced input. Don't really have any way to measure 
NF, but I can do MDS, I have a good calibrated generator. They both seem 
sensitive enough. I'll try to do an audio distortion test too, my 
service monitor has that function.

I've been taking the audio from the diode load to an external SS AF amp, 
so I haven't messed with the audio sections yet, but the line level 
meter works fine and I replaced a lot of audio caps and other stuff so 
they hopefully are good. I was listening to an Argentinian AM station 
today and the AGC seems to be working fine. AGC voltage runs around -9V 
with a strong station. AF sections will be right behind why the 14MHz 
band is not working, crystal no doubt. Luckily I've got 2 390A's so I 
can swap things around. Yeah, cell phone, ha. They actually sound lots 
better than my TS2000, but it's not even got 5K BW in AM. More like 4.5, 
heavy roll off above 3K.

The 2K mechanical filter I repaired for one of the IF's developed a 
short to ground in the input side so I need to pull it apart and see if 
I can fix it. It's got 50Ω on one side and gnd on the other so the coil 
is still good. I replaced the original innards with am FA type plastic 
filter, but it met spec when I sealed it. I've already got the filter 
out, just need to get set up to pull it apart.

One radio had SS replacements in the PS (and crushed sockets), so I got 
new tube sockets and re-did all the wiring and someone sent me some 
rectifier tubes quite a while ago but I haven't tested it yet. It worked 
with the SS, I just don't like the high B+ and the instant surge from 
the SS mod. I tried the thermister or whatever it was and it put out way 
too much heat for my liking, and still too much B+.

Dave N3DT