[ARC5] CQ "Command Sets" assistance needed

[Neil Barnett]

>PS: came across a series of articles on an AM site about how to use old
>high-voltage transformers as modulation transformers. Looks promising.
>Anyone done this? 

Tried it back in the late 60's with ARC-5 transmitter.  It worked,
but anything that was cheap and worked was deemed successful
in those days.

When the original center-tapped high voltage secondary is used
as a push pull modulator connection, the DC current flowing to one
modulator tube is balanced by the DC current flowing to the other,
so the flux in the core is very close to zero.  However, the ARC-5
plate current flowing through the other winding (original primary)
unbalances the transformer and tends to magnetize the core,
resulting in non-linear distorted modulation.

Real modulation transformers incorporate an air gap in the core to
minimize the DC polarizing effect, and there is an optimum length
of air gap for any particular out-of-balance polarizing current.  Few
power transformers contain an air gap (only those with very high
flux densities of 50,000 lines or more), so the odds of finding a high
voltage power transformer with the correct air gap are small to
non-existent.

A better solution to the problem of sourcing a modulation transformer
is for a group of AM enthusiasts to get together, decide on a push
pull output stage, example p.p. 807's/1625's, and obtain a quote from
a transformer company for a bulk order.  I priced such an order of 40
units from a local manufacturer a few years ago, and the price was
very reasonable.

73 de Neil ZL1ANM