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

[mac]

All,

In my experience the settling is down-frequency and takes 30 - 45 sec.  
on 40M.  Gets interesting on CW as the frequency will shift around  
according to the sending speed. It's also been my experience that the  
neutralizing adjustment is load dependent, i.e., if the initial  
adjustment made with a good dummy load (50 ohms resistive) may not  
"stick" when connected to an antenna feed line with other than a 1:1  
swr.  Advisable to go through the adjustment process described by Dave  
connected to the load one will be using on the air.

Dennis D.  W7QHO
Glendale, CA

************
On Apr 30, 2011, at 1:48 PM, David Stinson 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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