[R-390] Receiver Sensitivity

[Flowertime01 at wmconnect.com]

Roger,

Off you go to the Internet and find the R390 home page

http://www.r-390a.net/ R390 web page by Al Tirevold

http://www.r390a.com/ web page by Chuck Ripple

AL's page has the original TM's in adobe.

But you really want a copy of the Y2K manual the fellows wrote for what else 
the Y2K disaster year.


Get your favorite beverage and down load a copy of either the Y2K or the hard 
to read and follow TM 11 5820 358 35

The R390/A only tunes down to 500 Khz. So while you can dial it down under 
500Khz it is deaf. always has been likely always will be unless you do some very 
serious receiver changes. Don't ask me here. Those things are not allowed 
under the current administration and were even off limits under past 
administrations. Good Fellows do not do those kinds of things to boat anchors. But I 
digress.

The fact that you think you have 200 to 700 micro volt sensitivity across all 
the bands and any where tells you that the mechanical stuff is OK.

The hot spot at 3.8 is just a red herring to put you off the trail.

If the receiver has not had a cleaning in a while you are looking for some 
crud in a tube socket. Deoxit and some quality time are in order. Tube sockets, 
and sub chassis connector pins get treated first.

Likely the receiver was run until one or more tubes have reached the end of 
their useful life. Time to push all of them through a tube checker.

Get the TM and start with paragraph 73 gain adjust potentiometer R519. Input 
455 at 150 micro volts into J 513.  Hang any AC volt meter across the local 
line output with a 600 ohm 1/2 resistor. (2 each 1200 ohm in parallel). AC volts 
across a 600 ohm load gets converted to DB. (some math involved). Hang any DC 
volt meter across the diode load. Set the band width to .1 and rock the 
generator into the 455 crystal in the IF deck (under Z501). set the band width to 
2KHz. 

Set the gain adjust to get - 7 volts on the Diode load with the BFO off and 
the generator to CW.

With the generator on AM with about 30% modulation.

You expect about 1/2 watt on the local audio line out on the rear panel.

P = E/I = (E x E) / R 
P x R = E x E
  
.5 x 600 = E x E = 300 square root = 17 volts AC or some where around 27 DB.

Turn the generator modulation off and you expect to see a clean drop of 30 DB 
at the local  output audio level.

If a 150 micro volts will not drive the IF and audio to at least a 1/2 watt 
out put then you have an IF audio deck problem. If you cannot get - 7 volts on 
the diode load then you have an IF deck problem. If you cannot get a good 
clean 25 (30 preferred) DB difference in power on the local audio output with just 
modulation vs no modulation the IF deck and Audio deck tubes have too much 
noise and new tubes are in order. If you cannot get the signal to noise in the 
IF deck and audio deck there is nothing you can do in the RF deck to cover the 
IF audio deck problems. 

Once you get the IF deck and audio deck in order then you can start on the RF 
deck. Of course mechanical alignment come first in the RF deck.

Likely you just have a bad tube or some crud in a tube socket. The most 
common problems in the receivers these days. Your receiver has been recapped so you 
are OK on that front.

There is not any thing in an R390/A that cannot be fixed by you. The Military 
taught thousands of Fellows to fix these receivers. But like the receivers, 
most of the Fellows are getting old. There are a few holding out in Never Never 
Land with Peter but they have no RF there, thus no need for radio's.

Good luck with your receive and let us know what you find. That's how we 
Fellows learn what the problems are.

Roger L. Ruszkowski AI4NI
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