[Boatanchors] Lettine 240 Transmitter Plug In Coils

[LEE BAHR]

Right now I have two sources of old B&W Coils (JEL, JCL, MEL, and MCL) being 
sent to me.  I really appreciate the help being offered.  I know the plastic 
will be poor, wire corroded and bent, wrong amount of turns, links missing 
or in the wrong place, etc.  I plan to rebuild an entire set of coils from 
the above cores.  The coil bases will be the foundation for the new coils.

I see Surplus Sales of Nebraska has some decent pricing on small Air-Dux 
coil stock, so I plan to use some of it plus make my own coils where 
reasonably priced stock cannot be obtained.  I might even be able to use 
some of the coils from the cores I am about to receive.  Putting wax paper 
over a small form and then winding a new coil and then putting clear epoxy 
down in stripes seems to be the best way to go when making a SMALL coil. 
The more exotic collapsible forms would be better for large coils,  I would 
suspect.

I am confident I'll be able to produce a nice usable first class set of 
coils for my LETTINE 240 transmitter.  I plan to restore the electronics 
first and then work on the coils.

Lettine used a 50 pf C1 final tank resonating cap but B&W says you need 100 
pf for 160 meters.  I would suspect this will mean I won't be able to cover 
the entire 160 meter band with just 50 pf of variable cap.  (Not enough 
spread).  I can live with this in 2010 but I wonder why Lettine did this 
back in the early 50s when they knew 50 pf was too small for 160.  I suspect 
they figured hardly anyone would use it on 160 and 50 pf tunes more smoothly 
on other higher bands.  Bye the early 50s "link output coupling" was already 
on the way out and pi networks were on the way in.  Same with 807s.  They 
were being replaced with 6146 tubes.  When Leo Myerson of WRL came out with 
the Globe Scout 40A, it had a 6146, pi-network, and band switching.  The 
Heising modulation worked out just fine too.  The Lettine did in fact have 
true plate modulation to it's favor.  I think the Globe Scouts from the 40A 
on really must have done a number on the Lettine sales.

I've always wanted to play with a Lettine 240 and now 60 years later I can 
do so.

Lee, w0vt





Subject: Re: [Boatanchors] Lettine 240 Transmitter Plug In Coils


> Drew, et al. the major problem that so many of us experience with these
> small plug in coils, in particular,  is that the support strips or ribs,
> over time, begin to disentegrate   Perhaps, it is due to the RF energy
> reacting with the polystyrene support material - I am no chemist.  The 
> color
> of the materials actually turns from clear to slightly brownish.   From my
> experience, B&W coils are the worse for this problem.  Perhaps, someone 
> much
> more technical can explain this better than I can.
>
> David Knepper, W3CRA/W3ST
> Editor of the Collins Journal
> Secretary of the Collins Radio Association
> www.collinsra.com