[R-390] Gain drift

[dog]

Today I took out the RF section. Used some alcohol to clean the switches 
with an acid brush bristles cut short, there was some grease on the 
wipers I cleaned off. Checked the operation of each contact, seems 
normal, spring action seems good nothing is messed up. Used alcohol to 
take the wiper around the whole circle both switches to try to clean the 
contacts. The alignment seems OK, but there is an amount of backlash in 
the wiper, it centers the wiper better turning one way opposed to the 
other way, exactly like the other one I have. Pulled all the xtals and 
hit the contacts with a copper brush, new de-ox on the xtals and a bit 
on the switch wipers and a few places around the contacts, not much. 
Pulled and inspected every solder joint in the osc section, contemplated 
replacing the 5000pf bypasses but didn't. Solder joints all seem good. 
Back together, there seems to be somewhat less noise, but still the 
drifting gain on startup. Cooled it off for a while and pulled the input 
RF amp. Turned it back on and didn't see the gain drift issue but much 
less ACV on the diode load. I'll try it once more without the RF amp. 
And then maybe another RF amp tube.

I notice that with no inputs on the ant inputs, the RX is very sensitive 
to movement around the input ports. Like there's a lot of common mode 
currents making noise in the input. If I put a load on the balanced port 
it's much quieter. Of course if I sock a 50uV signal into the balanced 
input I get Carrier reading with AGC.

Did I read somewhere that if I use the balanced port I should short the 
unbalanced ports to gnd?

Do all these RXs make noise when changing the bands? I almost always get 
a big crackle when I change bands. But now as I rock the bandswitch on a 
particular band there's lots less to no noise. The 27M and the other one 
that seemed noisy before seem more like the rest now, stable. No issues 
tuning the output caps unlike yesterday.

Almost lost the Oldham coupler spring putting it back together today.