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Has any Decca Jeep owner considered using
ferrite cores for PA coils instead of altering the existing poor
quality paxolin air wound devices. The originals in spite of being wound with
litz wire are poor specimens, not even good quality at the time, when ceramic
formers and better were available and widely used in the USA.
Using the original coils the inductance when
measured in the case and out of the case varies by several Uh and therefore
difficult to resonate/align properly. For those that want to retain the
originals there is a way to overcome the problem with resonance, but I have not
seen any reference to it before.
Rewind the coils lower in frequency by a
few khz than is required and use a large copper ring in the core
of the coils for precise resonance, alternatively wind the coil higher in
frequency than required and use an appropriate ferrite core to adjust for
precision alignment.
The best approach is to discard the original
coils and rewind new coils on ferrite cores that do not alter in inductance in
or out of the metal cabinet. Each coil consists of the main winding and a
link winding. Each coil can be resonated externally with the pull
out capacitor board, to the exact frequency required, then replace without
further adjustment all three coils/capacitor boards.
Because each unit only runs at about 400 watts rf
out, 18 guage insulated wire is adequate.
If anyone is interested in the above mods I have
the exact inductance measurements for main and link winding. These values are
for the high band versions, low band versions need the capacitor boards modified
as well for 136 khz.
These Jeeps are big things, about the same size as
the Marconi Jeep, and a quarter the size of the Willis Jeep. A better solution
is to build your own micro jeep, more power and a fraction of the size as the
Decca.
Have luck de G3KEV
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