On Wed, 11 Jan 2006, Alan B. Pearce wrote:

>> Hehe. I just restored an old valved radio to life.
> ...
>> It is more sensitive with its 4 valves (some are
>> double) than the ICF-SW11
>
> Is it actually more sensitive, or just appears so because of lower
> selectivity?

It has very good selectivity. It uses a heptode oscillator-mixer, a 
pentode IF stage and two twin-tuned IF transformers. IF+RF gain for such 
a system can be >70dB with 30-40dB more added in the audio stage (2x 
pentodes). Image rejection is very good (the ferrite rod wound antenna 
coil has a high Q) and the air variable has specially crafted (different 
sized) moving plates for osc and rf, for perfect tracking. This radio is 
from ~1955 so it represents the sum of the lessons of the previous years 
probably. After that transistors quickly took over the market. (and all 
this happened a long time before I was born ...)

Peter
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