[R-390] My R-392 Starts Singing

[Dan Merz]

Hazama,  as best I remember,  my 392 worked right away like yours after I
put the power to it.  I then checked all the tubes on a tube tester and
replaced a few weak ones,  as I recall 26A6's.  I never had to do anything
else to the radio.  It's worked ok since,  now about 13 years later.  I
don't use it very often since I obtained a 390a and then a 390.  The 390
gets the nod nowadays.  When I do turn on the 392,  it never disappoints me.
The guy that talked me into buying it told me it would go forever with
little service because of the low plate voltages, and he advocated about 24
volts.  I have read that low voltage is a disadvantage,  and is made up for
in the design with more tubes in the i.f. lineup and moreover that 26A6's
and 26A7 suffer loss of gain,  or tend to be unpredictable in gain,
compared to tubes with higher plate voltages.  It sounds like your radio is
doing well for no tube checks yet.  I run mine at about 23 volts.  I suspect
it would operate better at somewhat higher voltage but I followed the advice
of a veteran military collector and built the unregulated supply that he
recommended with so much capacitance that I have to bring it up to power
gradually to avoid blowing the appropriate line fuse to the power supply.  I
finally added a delay relay so I didn't forget,  or have to use a variac.
It has the biggest cap I've ever used in a power supply,  54000 mfd, 30
volts, mostly chosen because it was there at the swapmeet for $1 and it gets
the voltage up with the transformer we found.  It's mate still is unused in
my storage cabinet.  I just went down and tried my 392 on 80 meters at 23
volts and 26 volts using a variac to see if I could tell a difference...yes
more gain at 26 volts (about 1/8 turn on the rf gain control) but band noise
was high enough and I had enough reserve in rf gain setting that it didn't
help on the particular station I was listening to.  The 390 was on in the
background and was much less noisy on the same station. I've got a Lambda
LMD24 supply that I found recently and I think it can be tweaked to up to 25
volts which might be a good replacement for my homebuilt supply to get a
little more gain, and maybe I should check my tubes again.  I think I have a
few spares to exchange in the set. Regards,      Dan 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Osamu Hazawa
Sent: Thursday, January 05, 2006 4:53 AM
To: R-390 at mailman.qth.net
Subject: [R-390] My R-392 Starts Singing

Hello All,

After a long period of time (more than a half year), I made a set of power
connector (made with a couple of But Splices) for my R-392 and  I set the
voltage at a little bit higher than 26V.

I was so excited when I turned on the radio.
At first, nothing was heard....
But I found RF Gain knob was turned all the way to CCW and rotary switches
for Megacycle have bad electrical contacts.

Yes, it started singing on BC bands!
But unfortunately, ANT Trimmer doesn't do the justice on all bands and CAL
tone was not heard on higher bands.

What do you out there think should I do first?
Open up the case first?

Any idea would be appreciated.

Osamu Hazawa
 http://www4.ocn.ne.jp/~pomerol/MyPage/menu0.html

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