[R-390] Help getting unstuck!

[Craig C. Heaton]

Hello Roger,

Taking a real close look at the top slug, cleaning the top, it does have a
crack. So its not going to move as one piece. Cecil's idea of a root canal
might be the best option if the receiver will not come up to specs. I'll use
this as an excuse to put out a general call for parts n' pieces! If someone
has a spare slug, T501, or a IF sub-chassis please drop me a line. The
Motorola will never be a museum piece, but it would be nice if everything
would work as designed.

In the coming days, I plan to go through the entire receiver and at some
point will be able to try the signal to noise test. Took the IF sub-chassis
out last night and looked at what it would take to replace T501, lots of
work. Root canal would save time vs the soldering iron to replace the entire
transformer.

Tnx,
    Craig

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of
Flowertime01 at wmconnect.com
Sent: Friday, April 01, 2005 8:38 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Help getting unstuck!



Can't seem to get the top slug in T501 to move.

Craig,

Sounds like a chance to stop and test.

Run the 455 into the IF deck and do a signal to noise test. If you can get a
28 to 1 signal to noise the coil is close enough and effort to adjust the
stuck slug will exceed return on investment. If its close just leave it
alone. If
its not close then maybe you will be loosing some fidelity in the 16K band
width.

Use the Adjustment of Gain Adj Potentiometer. Paragraph 73 in TM
11-5820-358-35. you want to run 150 uv of 455 into the IF deck. set the gain
adjust for -7
volts on the diode load. With 30 percent modulation you should get about .5
watt of audio across the 600 ohm output. We metered the headphone output
with a
test lead that ended in a phone plug. You can meter dB with most analog AC
volt meters and the instruction book (page of paper) for the meter.

Turn the signal generator modulation off. Now you have just a 455 carrier
signal. The audio output should have dropped 30 dB and there should still
be -7
volts on the diode load.

If you cannot get 30 dB signal to noise here, start swapping tubes around
and
trying to do some alignment. Trouble is there is no easy way to determine if
your IF deck was stager tuned or aligned at 455.

So try to perform the stager alignment procedure as detailed in the TM
first.
If you are loosing gain, go for the straight alignment.

Just leave the stuck slug for the very end. Get all the other bugs out of
the
way first. Get good tubes in and do the best alignment you can get other
wise.

If you get up to about 28 to 1 just leave that stuck slug alone.
Only after you get every thing else as best you can and you know by
measurement that the IF deck is not up to minimum then get worried about
that slug.

Get the cover off the can so you can see what's moving.
The hot air hair dryer is the least offensive way in.
Most of the time it will melt down some of the wax.
Heat and soften the gunk.

You can get an IF deck from Fair Radio less crystal filters and tubes, and
BFO and ballast tube. It will have a T501. The IF cans (T501, T502, T503)
are
all the same.

Push comes to shove and you conduct a destructive test, ask here on the
reflector, someone likely has the part stuck on some of there collected
spare parts
and would make you an offer your not likely to refuse.

Good luck and be gentle.

Roger KC6TRU





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