I want to build for Nostalgic purposes a mostly Tube Communications reciever or transciever for 80 and 40m with readily available parts, coils that can be duplicated, no Denco coils!...
I should have 455K/C cans...
Crystal filter is a must...
This might make a difficult combination, unless you have a
good source for the WWII crystals in the 455 kHz range.
It is much easier to build acceptable crystal filters using standard
off-the-shelf frequencies like 4.433 MHz, 6 MHz or 8 MHz, so
unless you are planning a double conversion design, combining
these two features will make things much more difficult.
(Although the double conversion isn't a bad approach in this
case, especially if you keep amplification at the first IF to
a minimum.)
There are ceramic resonators for 455 kHz that can be used
in shunt to make filters - a design using 500 kHz resonators
appeared in
Technical Topics, and that might be used
with your 455 kHz transformers, although the load impedances
might not be ideal.
A number of solid-state designs used 10.7 MHz IF transformers
with additional shunt capacitance to tune them to lower
frequencies, sometimes down to 80m. If your junkbox includes
some old FM broadcast receivers, this approach might work.
If you choose an IF in the 5 - 6 MHz range, then a single VFO
around 2 MHz would only need a small change in frequency
(or possibly none at all) to cover both 40m and 80m, assuming
you don't mind the tuning working "backwards" on one band.
Lower frequencies are often easier for designing narrow CW filters,
while wider filters for SSB may be easier in the 8 - 10 MHz range.
Remember, while audio filters are commonly implemented using
op-amp IC chips, there are designs using tubes as well, as well
as passive designs (some using the old 88 mH toroids).
Coils for tuned circuits can be wound toroid cores (if that doesn't
spoil the desired aesthetics, of course), which are relatively easy
to adjust for the number of turns on various links. The coils
themselves won't be easily variable, but they can be tuned with
trimmer capacitors if you don't have slug-tuned coil forms
available. (You can always hide such modern items inside the
cases from junked transformers.)
In the end, the decision will probably be based on what parts
you have on hand or can get easily, what features you want, and
the desired aesthetic. For covering both the CW and SSB
portions of the bands (especially the Region 2 80m band from
3.5 to 4 MHz), tuning rate becomes more critical, especially for
SSB, or CW with a narrow filter. That might require separate
bandset and bandspread controls, multiple VFO tuning ranges,
or cascaded vernier drives.
While AGC is nice, I spent my novice years riding the RF gain
control (the BFO signal leaked into the AGC circuit), which
simplifies things.
Do pay particular attention to the various mixer products when
choosing your IFs. I have a bunch of 10.7 MHz crystal filters
that seemed like they would be great for building SSB radios,
but on 40m the second harmonic of the oscillator is in the
desired output range, so filtering becomes a nightmare. (And
operating on 21.4 MHz is a real challenge!)