"starman" wrote in message
...


The most common tube type AM radios (5-tubes) used a two gang tuning
cap' for the front-end tuning and oscillator but I think there were some
cheap models with no front-end RF amp' or preselection tuning. The
antenna was connected to the mixer which had some gain to off set the
lack of an RF amp' stage.



Armstrong's first superhets didn't have a tuned RF stage, but those radios
were designed to operate at frequencies too high for the TRFs of the WW1
era. Something like 3 mc, if I recall. There wasn't any interfering
signals at the image frequency.`

I'm not aware of any commercially available AM superhets without preslection
and such radios would have a big problem with images 910 kc above the
intended frequency. The images would include other stations in the
broadcast band, the old Loran buzzsaw, hams on 160 meters, etc. Few AM band
only radios had RF stages, and most of those were simple RC coupled stages
for extra gain, but not selectivity. But, as far as I know, they all had a
tuned loop antenna or antenna coil.

Frank Dresser