[HBR] HBR with switched coils

[Walt Hutchens]

John said:

> Hi,Has anyone got any experience of using a wavechange switch or
> reed relays in place of plug in coils?I was going to use reed relays, any advice?

The central concept of the W6TC receivers is using LARGE coils
designed for high Q in a manner that gives leads short enough for good
stability.  In the 1950-60 time frame that could only be done using
plug in coils.

With just one coil set in the receiver at a time those coils could be
located close to everything. That's the key to the ability of these
receivers to outperform virtually everything else in the ham market at
the time.

Shrinking the coils to keep short leads when using a bandswitch cut
the Q by maybe a factor of four; keeping the big coils when using a
bandswitch meant long leads -- stray couplings and VHF oscillation
problems. You can test almost any commercial receiver of the period
and see how 'small coils' worked out.

Now there are other ways to go. Replacing the big solenoid coils with
medium-size toroids (RF and mixer stages) and smaller coil forms for
the oscillator will work fine and would allow your choice of
bandswitch techniques. It's still not a trivial exercise -- you have
to find room for the trimmers, oscillator stability will be tough with
poorer cooling of the oscillator coils, and optimizing the layout is a
chore -- but it IS doable.

I don't know that there's any particular reason to prefer one kind of
switching over another. Reed relays certainly give you layout
flexibility.

Walt
KJ4KV