Looking through my junkbox I found a roller coil and several larger
variable capacitors that I had put away some years ago with the idea of
building a 'transmatch'. I have one 250pf and two 500pf variables,
probably in the 300 watt category (which would be fine for me). In
looking over QST articles I see three different possible configurations:
1: the Ultimate Transmatch from 1970
2: the SPC transmatch from the late 1970's
3: the "T" network

From what I've read, the old Ultimate circuit had a good wide range and
low loss. It's bad point was that it could act as a high pass network
instead of a band pass network in some settings. This means it would
have very little harmonic suppression. The SPC circuit would always act
as a bandpass network, but in some settings it's loss was high. As a
result both of these have fallen out of favor these days. The "T"
network is what most current antenna tuners are using. Yet the "T"
network has two problems: 1: there are many combinations of settings
that will yield a good match but many combinations result in high
currents or high voltages across the components resulting in arc over or
smoke. 2: The "CLC" "T" network always acts as a high pass network so
has little harmonic suppression. (The "LCL" "T" network would act as a
low pass network, but would require TWO variable inductors and cost
quite a bit more).

The reason why the "T" network is acceptable today is that most modern
transmitters have enough harmonic suppression that the antenna tuner
does not need to add any more. With this in mind, it would also appear
that the older Ultimate Transmatch circuit would be acceptable today.
It does not have the high loss of the SPC or the 'cranky' behavior of
the "T" network.

I think that I can use the two 500pf variables (Johnson 500E20) as the
dual section part of the circuit by ganging them with insulated
couplings and mounting the capacitors with ceramic standoffs. They are
twice as large as what the original circuit called for though. The 250pf
(Johnson 250E45) variable will serve as the series capacitor. It also
needs to be mounted on ceramic standoffs. The roller coil has one end
with wide spacing.
I also have two national 'velvet vernier' dials for the caps and a turns
counter dial for the coil.

Has anybody out there experimented with these circuits, what results did
you get?