[R-390] My R-392 Starts Singing
Barry Hauser
barry at hausernet.com
Fri Jan 6 01:26:41 EST 2006
Dan, Hazama
IMHO the R-392 is probably one of the most neglected receivers in terms of
use and maintenance. This, I offer, is due to the fact that (a) they're
small, (b) require a DC supply (c) usually operational on delivery or after
a bit of tube replacing, (d) are usually unhacked so don't require
un-hacking, (e) have sealed cases so no corrosion, weathering, dust inside,
and a couple of reasons I'm probably forgetting. Well, one indication is
that many of us have them, but they rarely turn up in threads on this
reflector -- almost as if they're a member of the family who should not be
discussed in mixed company ;-).
I have several. All work. One day I bothered to do a full -- or mostly
full -- alignment on one of them. Quite a difference. Decent performance
became very good/excellent performance. So do take the time to go through a
full alignment. Chances are, the mechanical alignment is good, but the
coils etc could benefit from a touchup.
When tuned up with good tubes, performance is very close to an R-390/R-390A.
There's something on Josh Rovero's web site about detailed comparisons. One
limiting factor is the choice of bandwidths vs. the big ones and the AGC
adjustment, but otherwise he found the sensitivity and selectivity to be
nearly identical.
As for voltage, nominally these are 28 volts which represents a 24 volt
vehicular power source. These normally vary between 24 and 27.6 (27.8?)
volts depending on generator/battery/engine RPM's. There are actually two
separate pins on the 9 pin connector for filament and B+. The word is that
best performance and tube longevity can be obtained by running the filaments
at 24 volts and the B+ as high as 32. Of course, that means two separate
power supplies, so a happy medium might be the 26 vdc. You could use a
beefy 24 volt supply and a lower current bench supply to provide the B+ I
guess.
Due to the relative smallness, but sturdyness, R-392's have a tendency to
wind up under the bench or in a closet with stuff piled on them, so often
have to be dug out before use. The big gray ones can't hide in small spaces
that well.
Suggest you check out Josh's R-392 web pages if you haven't found them
already at http://www.roveroresearch.com/r392/r392.html
OK, remembered another possible factor. To get audio out of these radios,
the easiest and most authentic thing to do is use an LS-166 speaker that
already has the UG audio connector, so it's plug 'n play. However, the
LS-166 is designed to be concussion-resistent and waterproof. It has inner
and outer protective perforated baskets enveloping the speaker cone and the
suspension is very stiff. They are, in effect, acoustic suspension
enclosures (no ports) but with the opposite of the high compliance driver
that hi-fi acoustic suspension speakers typically incorporate. As a result,
the sound is fairly crummy. Sound quality can be much better if fed to a
normal speaker through a 600-8 ohm transformer. Or, you can tap into the
matching transformer inside the LS-166 and run it to another speaker or use
an amplified speaker adapted from a computer speaker package right off the
600 ohm output. One of these days I'm going to slightly modify one of my
LS-166's -- install a mini phono jack which will cut out the internal
speaker when an external one is plugged in. I just need to get a round
tuit. Square ones don't seem to work so good.
enjoy ..
Barry
> 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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