[Comment and question on NC-100 toward the end]

John Byrns wrote:

...if you are referring to a channelized TRF approach to receive all
117 or so MW channels, then I would think you wouldn't need to go to
the bench at all to realize it isn't practical. A smaller number of
channels, say half a dozen or so might be practical.

I think 15 or so channel slots will be fairly easy to implement, and
nearly all metropolitan areas I know of probably don't have more
than 15 stations of sufficient power and fidelity to make it worth
tuning any more (or the end-user will not want to listen to
conservative talk radio, but will listen to ordinary news, sports,
oldies, and progressive radio stations, etc.)

Again, the idea of the channel TRF approach is to be able to really
fine tune the bandpass filters for each channel. Several here say it
simply won't work, and I scratch my head on this one since the
simplest is to take an existing working TRF circuit using a variable
capacitor to tune the radio, remove the tuning capacitor, and replace
each gang with a fixed capacitor of the right value (probably with a
trimmer capacitor to fine tune the center frequency) -- it is now a
single channel receiver, and should work identical to the original
circuitry, but now it won't tune.

Now, can't one now extend this, and alter that part of the circuity,
adding LC components with the right value in the right ways to improve
the bandpass shape and proper electronic interfacing with the
properties of the RF section for that particular frequency? Obviously
the problem is figuring it all out, but one now has a lot of degrees
of freedom to work with -- no need to compromise any more as is needed
whenever one tries to continuously tune the circuit. I assume if one
can optimize it this way for one frequency (say the midpoint of the AM
band, around 950 khz), then one can then optimize it for each channel
in the 500 to 1800 khz range by simultaneously changing the values of
all the LC components as needed.

Of course, the question is how much is gained in performance taking
this approach. If several here believe it will make little difference
in real-world performance, then it makes no sense to even consider
the channel TRF approach, at least for high-fidelity purposes.

*****

Now moving to classic super-hets, the mention by John Byrns of the
National NC-100.

I think the best approach for the all out audiophile would be the
one suggested by Randy, or was it Sherry? Gutting out a National
NC-100, and rebuilding the band selection assembly with 5 sets of 3
optimized band pass filters to segment the MW band into 5 parts.

I recall last year a few people mention the NC-100. Is this radio
reputed to have excellent audio fidelity (I suppose when the variable
bandpass control is set wide) in addition to excellent selectivity and
sensitivity? And can the circuitry be modernized (e.g., modern tubes),
etc.? The idea of making it a 5 band AM radio is certainly
interesting.

Jon Noring