[R-390] Test Equipment Question

[Miles B. Anderson, K2CBY]

If you're cutting down to the essentials I really 
don't think you need anything more than you've got.

If you need an audio generator you can take 
400 Hz and 1kHz from the URM-25.

An RF probe for the VTVM is helpful but you've got 
to be careful that the input capacitance is small 
enough so that you don't overload the citcuit and kill 
off the signal you are trying to measure.

I have several scopes in the shop but frankly I've 
never needed to use one to service an R-390A, though 
it would be handy to check whether the crystal 
oscillators are running. (I've also used a scope with 
a vertical amplifier output to act as a preamplifier 
for my frequency counter.) 

Perhaps the best oscillator check in the absence of 
a scope is to listen on the oscillator frequency 
(or multiple) with another receiver. You can also 
use the VTVM to check the dc grid voltage 
to determine whether an oscillator is running. 

The only other service tool that I have found 
really useful is an EICO Model 950 R-C bridge 
to measure capacitor values & leakage, but you 
can live without it -- especially if you intend 
to re-cap the R-390A.


Miles B. Anderson, K2CBY
16 Round Pond Ln.
Sag Harbor, NY 11963
Tel.: (631) 725-4400
Fax.: (631) 725-2223
e-mail k2cby at optonline.net