Uncle Peter wrote:

The majority of sets I collect seem to have equal sized plates in the
osc. and mixer/rf sections? I don't think the offset oscillator section
came
into vogue until the late 30s or early 40s??
===============================
All multi-band radios use equal sized tuning capacitor sections in the
local oscillator (LO) and Mixer/RF stages. Padder caps are used to
adjust the oscillator section to provide proper tracking.

Single-band sets often use a so-called "cut plate" tuning cap with a
smaller oscillator section. This eliminates the need for a padder
capacitor. But, the size of the oscillator section depends on the
relationship between the IF frequency and the tuning range.
Multi-band sets would need a different sized oscillator section for
each band. That is why the equal sized section tuning capacitor is
used in multiband sets and padder capacitors are used to reduce the
oscillator section capacity to the proper amount for each individual
band.

The top band on many low-cost, single-conversion sets (like the S-38
series) don't use a padder capacitor since the IF frequency is such a
small percentage of the signal frequency. These are the sets that
often have the LO on the low side of the signal frequency. If a
padder capacitor is used in the oscillator section, then the LO is on
the high side of the signal frequency for sure. If no padder is used,
then the LO may be on the high or low side. Unfortunately, the
alignment instructions seldom state the LO location. On the
Hallicrafters S-40, the LO is below the signal frequency on Band 4. I
determined this by experiment.

All this stuff is discussed in detail in the Radiotron Engineers
Handbook, 4th Edition, beginning on page 1002.

Best Regards,

Ed
Canyon Lake, TX