[R-390] HELP ! Deaf R-390A

[Roy Morgan]

On Oct 26, 2015, at 2:28 PM, Craig <hamfish at comcast.net> wrote:

> Hi Rick,
> 
> Start in the beginning. Inject, using a sig-gen, a modulated signal into the
> balanced antenna input. Follow the signal thru the receiver with a scope &
> tube extender.  

Rick,

Divide and conquer.

No tube extender needed (though they are VERY handy).

The RF deck has a number of test points, many at the grids.  Get a signal generator warmed up, study the manual till you know what frequency signals are expected at each test point, and inject that signal (use a series capacitor on the signal generator output)**.

Start at the input to the IF deck.  150 millivolts modulated 30 percent (or is it 100) should get you a standard output (half a watt audio?)  Use the line output meter because that’s convenient.

Then go backwards toward the RF stages and see where the signal quits.

**The URM-25 signal generators had an adapter with just a single series capacitor in it for this purpose.

If there is not info on the web somewhere about what signal levels are to be expected stage by stage, I’d be surprised. As a rule of thumb, each stage in RF or IF strips may have a voltage gain of 10.  Wu Li’s Pearls of Wisdom pages are an astounding compilation of info and experience.  The only trouble is that the one on the IF section is many hundreds of pages long!

Roy


Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958