[ARC5] [Milsurplus] BC-375 on 40 Meters? You Bet!

Sat Apr 30 23:36:06 EDT 2011

Dave

I will second your enthusiasm for the BC-375. I actually run a BC-191 with
the Original power supply. Time was when running one of those would get you
a pink slip, but now pretty much anything goes, and as it should be. It is a
historical rig which looks stunning when operation, if you leave the cover
off. I run my with a BC-342. This actually makes up the SCR-193. I guess to
be totally correct I would run the BC-191 and the receiver off dynamotor.
But it is good to hear the use of this great piece. And a good tip about
using the service monitor.

Roy WIldermuth
AWA Museum

On Sat, Apr 30, 2011 at 4:48 PM, David Stinson <arc5 at ix.netcom.com> wrote:

> I love it when people tell me I can't do something,
> like:  "The BC-375 won't work on 40 meters."
> Oh yeah?
> Just had a good QSO on 7160 KC and
> will be joining the net there this weekend.
> The rig drifts down about a KC after key-up,
> then settles, but what of that?
> As a friend used to say;
> "Whaddayawant?  Egg in ya beer?"
> If a person is using an AM detector
> as The Almighty obviously intended
> for these nets, 1 KC's not a problem.
> And it sounds as good as it does on 75 meters.
>
> There are three keys to getting a 375
> to settle down on 40:
>
> First- Make sure you have good tubes.
> I had a stash of about 20 untested 211As.
> Once I got the rig going, I tested each one
> in the 375.  I now have 12 good ones
> (and two less HV fuses).
> Most had gone gassy.  Some had open fils.
> Two had no emission.  One of those got fixed
> by re-heating the fil pins with a frame iron.
> The other I tried to "rejuvenate" and it worked,
> at first.  Then I accidently popped the grid with
> B+ while the fil was "cooking" and now the tube
> has incurable grid emission.... rats!
>
> Second-
> A good ground plane under the whole rig
> and a good ground connection.
> Thank you, Mike Hanz, for waking me up to this.
> You can see my SCR-287, which is undergoing refurbishment,
> by looking-up AB5S at QRZ.com.  On each of the three shelves
> (PE-73 dynamotor and power supply out of frame on the bottom)
> and up the back of the wooden rack is a pattern of aluminum
> "duct" tape you can get at any "home despot"store.
> Each shelf has a cross-hatch of four runs which
> go from edge-to-edge and are spaced to make full contact
> with the shock mounts, dynamotor and supplies.   Where the tape
> crosses, either a portion is "bent under" to make contact or
> a small piece is folded and placed across the two runs
> to make a contact point.  Another small piece of the tape
> over the "fold" secures this down and makes a good contact.
> The shelf patterns are then tape-connected to the vertical.
> All is painted-over except for the places where the shock mounts
> and other pieces need a ground contact.  An ohmeter from the top
> of the transmitter to the bottom shelf reads a few ohms, and that's
> just fine.  The station ground hooks to the rack ground plane
> and you're good.
>
> Third:
> Careful neutralization.   This is tedious, but not as "scary" as it
> sounds.
> If you have a service monitor that can show you FM deviation,
> you're in "high cotton."   If not, you need a good receiver with
> a narrow filter (2.8 KC SSB will do) and a bucket of patience.
> Set your monitor receiver to SSB (yes... SSB).
>
> Warm-up the rig for 15-30 mins.
> Tune up the rig into a dummy load in "VOICE."
> Unscrew and remove the tuning chart.
> Under it, you'll find an adjustment wheel and a locking screw.
> Unlock the wheel with a quarter-turn on the screw.
> The wheel is your neutralizing control.  It will have a mark on
> it that matches one on the face of the tuning unit.  Unless something
> is wrong with your tuning unit, the "sweet spot" that will stop
> the FMing is going to be within a few degrees of that marked point.
> Use a "locking bar" key to put the rig in transmit; you're going to
> need
> both hands.   Let the rig settle. It should only drift down about a KC
> before settling.  If a lot more, you have a problem in the tuning
> drawer.
> Set your monitor receiver off zero-beat so you can hear the carrier at
> a few hundred cycles.  Say "FOOOOOOORE" into the mike while
> listening to the low beat note.  If you have a tone generator to use
> for modulation, so much the better.  If the rig is FMing,
> you will hear the beat note go "ragged" under your modulation.
> Raspy.  Tweak the wheel a degree or two.
> Tune the MO until you get the same
> beat note again (the neutralization control will pull the MO)
> and repeat the above.  Do this until the beat note
>  sounds more "solid" when you modulate the rig.
> Then set the receiver on AM and carefully, gently tweak,
> retuning the MO each time, until your audio sounds best.
> We're talking small movements here.
> I use the tip of a jewelers screwdriver with my hand
> resting on the tuning unit.
> The upside- once this is done, it will "stick" until you change tubes.
>
> Don't let it scare ya.... go for it.
>
> 73 Dave S.
>
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