[R-390] New Project (Progress)

[Jim M.]

Some random thoughts:
If the mechanical alignment is not sync-ed to the PTO, your sensitivity will 
suffer some.  The preselector circuits are very selective and if not synced 
to the PTO, it will suffer.  Just for comparison I usually get between 30 dB 
and 50 dB carrier level on the calibrate signal on the mid bands, even 
higher on the broadcast band.  So get the mechanical side lined up with the 
PTO before trying to fix anything else.

On SW bands the big stations (7 Mhz range at night) should be booming in 
with midscale to 3/4 scale carrier levels on a good antenna.

Be sure all the slugs are moving up and down without sticking too. 
Sometimes the slugs stick in the coil and a rack will not move as it should. 
The slug racks should each have two springs to keep them seated.  Press down 
on the racks gently as you tune to see if they seat better - if so then a 
slug is probably sticking - there's a way to fix that too - later.

The plug in crystal oven does heat up on my radio even with the switch 
turned off.  That is normal.  The oven switch only turns on the PTO and Xtal 
Osc chassis oven.

I have aligned a 390a pretty well with just the built in calibrator and the 
carrier level meter to work with.  It's not perfect but it works.  The Y2K 
manual has an alignment procedure using an external signal source but it can 
be done with just the calibrator signal.  But first be sure the mechanical 
parts are working together with the PTO.  And since you had one loose 
coupler, check the other couplers that you can get to - if a coupler 
somewhere in the other gear trains has loosened, then the problem may become 
more difficult - lets hope not.

An interesting experiment is to tune to a strong signal, then watch the 
carrier level meter as you slightly rock the MC change knob back and forth. 
If the meter wants to start peaking either side of the detent, you are out 
of mechanical alignment.  You can also pull up gently on the slug racks and 
watch the carrier level.  If it wants to peak anywhere other than at rest, 
then the mechanicals are off.  Get them synced with the PTO - an easy way as 
I said before is to loosen the PTO clamp, tune it to a known station or 
calibrate signal, hold it there and then turn the KC knob for maximum meter 
reading - with the PTO held still, what that does is peak the mechanics to 
the signal.  This will be a start only, from there a realignment may be 
needed (as described in the Y2K manual).

Other things could be happening - such as bad oscillator crystals, but that 
comes later.  Good luck.




----- Original Message ----- 
From: "Carole White-Connor" <carolew at bellatlantic.net>
Cc: <r-390 at mailman.qth.net>
Sent: Thursday, February 22, 2007 10:33 PM
Subject: [R-390] New Project (Progress)


>
> Well, we're getting somewhere:
>
> 1. The PTO problem was a loose coupler. I loosened a clamp, fit the ridges 
> and
> indentations, tightened it up, and it works. It's 25 khz off but I'll fix 
> that
> later. You folks pointed me in the right direction there. Thank you.
>
> 2. I have reception on all bands. However, there is a lot of hiss/static 
> and
> sensitivity is not where it should be. This may be a long-standing problem 
> with
> this radio. I see that the IF gain is set at max. If I back it off a bit, 
> I lose
> a lot of sensitivity. Any ideas? Reception is consistent on the bands 
> above and
> below 8 mhz. The noise limiter works well to remove a fair amount of the
> hiss/static.
>
> 3. I tested the tubes and replaced 4-5 that were weak or had shorted 
> elements. I
> noted minor improvement.
>
> 4. Reception on the 0-1 mhz band is really lousy. Strong BCB stations come 
> in
> weakly. This is the only band that is this bad. (The 2-3 mhz band may be 
> bad,
> too, but I haven't played with that band too much).
>
> 5. The crystal oven heats up even though the switch on the back is off. I
> disconnected a lead from this switch to disable it, but the oven still 
> heats. Is
> this a problem? Is there an easy way to disable it?
>
> 6. On a strong local AM station, the audio is strong and clear. On the 
> strong SW
> stations I receive, the audio is good, too.
>
> I'm just wondering where I should go and what I should do next. Again, my 
> test
> equipment is limited to a VTVM, signal generator and tube tester. So far, 
> I'm
> having fun with this set and am learning a lot. The Y2K manual is a 
> amazing. I
> wish I had something comparable for every set I work on. Any ideas or
> suggestions would be gratefully appreciated!!
>
>
> Joe Connor
>
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