[ARC5] The value of MO and PA tank components.

Wed Mar 23 20:24:01 EDT 2016

  Hi John,
  I have a "junk" '457.  Missing cover etc.  A real mess, but in a
  condition that can be put on air.  (but not safe w/out a cover!)

  I  am considering sifting the 4-5.3 MHz coverage "down" to the 80m
  band.  
  (Here, in Australia, this is from 3500 to 3700kHz)
  I have access to a lathe, and I can make a new calibrated dial.  
  I already have the aluminium plate, and (like most 'hams') I have a
  frequency counter to calibrate the dial.
  (Certainly easier to use than the gear available in the Bontoon labs.)

  Some time ago I made a nice "outer" box for some receivers
  (plywood/varnish) and the result "looks" late 30's or early 40's.
  The set slips into the box, and is well protected from dust etc.
  Putting the '457 in a box like this would solve the problem of exposed
  high voltages (on the PA plates), and present a "period" case.

  Now, with that background I can answer your question:  How much
  precision do I need?
  Answer:  Enough precision to allow me to calculate what will happen if
  I "pad" the existing components to bring the coverage down to (say)
  3400 to 3800 - or whatever is possible / turns up in the calculation. 
  In particular, can I 
  (1) retain the 'tracking' between the MO and PA stages.  (The answer
  is found in simple maths if the tank coil values are known)
  (2) retain a reasonable loaded "Q" for the PA.  (Increasing "C" will
  decrease "Q" and increase the harmonic content to the aerial.)

  I don't think the calculation needed to answer these questions is
  difficult. 

  I would like the finished project to present well - i.e. look
  professional and avoid the appearance of a "hacked" piece of gear.

  At the same time any-one with a knowledge of these sets would
  immediately say,  "not original".  
  I don't care!  This will be  a post-WWII "ham" modification,
  professional done.

  I take the view that the post-war use of these sets in amateur/ham
  service is as much a part of history as their role in the war -
  provided the finished article doesn't look like something good that
  was later 'bastardized' by a mad-man with a hacksaw and drill.

  That's the reason behind my search for info about T53 and T54.  In the
  end I may get the answer to my question by calculation (I already know
  some values, or I can measure them).  Alternately, I can 'cut & try'. 
   A working set has 10x the value of a perfect set 'on the shelf'

   73 to you de Les Smith, and thanks for answering!
   vk2bcu at operamail.com

On Thu, Mar 24, 2016, at 06:01, john rose wrote:
> How much precision do you need? The condensers have been measured and
> reported about a half zillion times, mostly on eBay.  Someone going to
> estate sales or flea markets looking for old electronics "stuff" will
> find one of these and list it as 'old variable cap' or some such.
> Nominally the reported value is about 35 mikeymikes to about 150
> mickeymikes. Check out this example.
> eBay item number:252316803695
> This value is what was reported in 'the literature of the day', ie
> conversion manuals.
> 
> I don't recall anyone listing the coils and transformers values and that
> is where the 'fun stuff' starts. C63, tuning, is in parrallel with C60,
> padder, and C68, fixed 3 mikeymikes temperature compensation. The Army
> manual lists 4 (count 'em) different rotor/stator angles, one for each of
> the transmitters, from 77 1/4 degrees (yeah, right!) to 95 1/2 degrees.
> That implies there is 'a heap of mathamagic' in trial and error
> calculations. Good luck. I am thinking I might take time out to
> physically measure the coils and see what my ARRL slide rule tells me.
> ________________________________________
> From: ARC5 <arc5-bounces at mailman.qth.net> on behalf of Leslie Smith
> <vk2bcu at operamail.com>
> Sent: Wednesday, March 23, 2016 2:57 AM
> To: ARC-5 List
> Subject: [ARC5] The value of MO and PA tank components.
> 
> To all:
> 
> I wish to learn the values of the oscillator and PA tank components in
> the ATA, SCR and ARC-5 transmitters.
> 
> These are, for the oscillator:  T53, C60, C63 (M.O. turning) and C68.
> 
> For the PA Tank circuit: T54A & B, C65 (PA tuning), C66 and C67.
> 
> The manual gives the following information for T54:
> 
>     Frequency          Dwg #  (from WECO)
>      3 to 4 MHz        7347
>      4 to 5.3             7248
>      5.3 to 7             7249
>      7.0 to 9             7250
> 
> Information is given in Table #20, page 126 in hard copy. (or page #141
> in PFD numbers) about these items, but not the value (uH, pF).  I
> presume this is because different values are used for the different
> frequency range in each type of transmitter.
> 
> I searched the tech manuals to my best ability.  My point here is that
> I'm writing AFTER making a diligent search, rather than trying to avoid
> this work.
> 
> If anyone on the list can advise where I might find component values for
> the tank components I'll be grateful.
> 
> Thank you,
> 
> Les
> 
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