[ARC5] SCR-183 Transmitter: Essential Knowledge and Tips for Revival, Part One

Tue Nov 16 10:25:31 EST 2021

 Dave,
After I looked at the SCR-183 TM, I had even more questions! Such as the 10 and 45 tubes have 2.5V filaments in series , that's good for a 5V input.The TM says the radios take 14 to 24V input. Where's the filament ballast? Is it in the control box?
That being one question, the other about inter stage cathode feedback concerns was addressed with your post.
The next thing is the bias "seen" by the new tubes is very different than the originals. I have no idea how they designed circuits with the old direct heated VT's, so I'm going to make an ASSumption.  If the filament voltage is 2.5, the average voltage there is 1.25V . This would be essentially the same as a negative 1.25V at the grid. Perhaps the top of chain will see 5v-1.25v and the bottom will see 1.25V

Now the new tubes have a 12V input with a cathode connected to the filament which will experience 6V or  the full 12v (-12v at grid) and the bottom could see either 6v or 0v depending on which side of the filament the cathode connection is made.
How much affect ( if any) did this have on the circuit?

    On Tuesday, November 16, 2021, 02:29:00 AM EST, David Stinson <arc5 at ix.netcom.com> wrote:  

I've been working and experimenting with SCR-183/283 
 for a long time.  It's the "Rodney Dangerfield" radio-
 "it don't get no respect."  That's an injustice, because it's
 a very important set with a long and distinguished service
 career, spanning 1931 until the end of WWII in U.S. Military
 use and years longer outside the U.S. and in the Civil Aviation.
 I check-into local AM nets with good reports.

 SCR-183 sets made by Western Electric in their Kerney, NJ
 plant flew in Jimmy Doolittle's 1942 12-Volt B-25 
 Bombers in their famous "Bombs Over Tokyo" raid.
 The transmitter is simple and, if one pays attention to these
 pointers and tips, easy to revive and operate.

 If you supply well-regulated B+ the Master Oscillator is
 very stable and reliable, even on 40 meters.
 I have a BC-230 transmitter which was (slightly and successfully)
 modified for crystal control on a 3 MC frequency.
 The simple, reversible change works for 40 and 30 meters. 
 Attached is an .mp3 of BC-230, crystal controlled on 10.110 KC
 (5055 crystal, double in the PA.)

 Been trying to write a concise-but-through
 manuscript for a gentleman for months but keep not 
 getting it done, because excuses. including the lose of
 a thick notebook of hand-written notes, charts and experiment
 results.  Makes me sick to my stomach every time I turn
 the place over again looking for that book.  Fortunately,
 I do have copies of illustrations I saved as files and
 posts full of info, some of which was obsoleted/superseded/corrected
 in that notebook.   It's got to be here... somewhere...

 This thread has inspired me to try try try to FOCUS and
 create something useful both here and for him on -183.  
 So decided to break the job up into smaller bites for here
 and flesh it out later for there.  Staying on-task has gotten
 very hard, but not impossible.  So enough whining.  
  "Your work and patience will be rewarded." 

 There are a series of issues to investigate/work when
 reviving a BC-230/430.  We'll write a post for each
 and work through them one-at-a-time.  Some of them,
 I'll need to put the rig back on the bench and redo
 to work I did long ago, because the charted results
 and "current" recommendations are in that blasted
 book.  Those charts are probably joining all the other
 data in there, stuck in some dark corner where I
 probably put it myself, laughing at the old doofuss
 every time I look right at it and don't see it.

 1.  Inspection and Base Condition.
      Determining basic condition, missing bits,
     lubrication, fixing low-Z grounds, De-Ox-it
      where needed, testing the
     mod transformer, replacing leaky caps etc.
      The base-line stuff we do when starting
      any boatanchor revival.

 2.  Deciding what tubes we'll use, how to 
      mount them for use.  CW only or CW/AM?
      Filament issues. Intro to Biasing issues.

 3.  B+ Power supply needs and issues.
      Regulation required for smooth operation.
      Relay (or relay-ish) keying as-designed, 
      recommendations.

 4.  Transmitter plug-in coil:  Common issue
      with the Neutralization coil and how to 
      fix it.  Pre-setting your coil tuning taps
      and cap.  External matching cap requirement.

 5.  Making a Neutralizing tool. Neutralizing.
      Measuring PA current.  Tuning-up.  
      "First Light"  and first QSO.

 We'll tackle other gremlins as they dare 
 bother us.  It will be fun.

GL OM ES 73 DE Dave AB5S                                                   

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