The BC-453 was used to sharpen IF selectivity on superheterodyne
receivers by tuning around the passband of the ~455 "kc" IF frequencies.
It was known as a "Q-Fiver," and added a second conversion stage down
to the 85 kc IF of the command set. Why not play with regeneration at
the BC-453 IF level, if you think you need it? (The regeneration scheme
works--I used it on several old receivers, and a WW II tank transceiver.)

If you are worried about Images with your mixer scheme, you may want to
look into some RF selection/amplification before the mixer. Back in the
Fifties and Sixties, one-tube PreSelector projects were popular,
(several good receivers, such as the Drake 2B, had them built in). The
extra tuned circuit should reduce your image.

--W9NPI

Antonio Vernucci wrote:
I would like to build an old-style receiver using a BC-453 stuck at
500-kHz as IF chain. A possibility would be to put a pentode in front of
the BC-453 mixing the incoming RF signal with the signal generated by a
variable local oscillator (VFO). To improve selectivity, one could adopt
a regenerative arrangement whereby part of the pentode plate signal is
fed back into the grid (by inductive coupling), and the cathode resistor
is then adjusted just before the tube starts oscillating. In other
words, a kind of Q-multiplying converter (I think this is called
"Q-dyne" receiver). What I am not fully sure about is if the increased
selectivity I so obtain turns into a higher rejection of the image
frequency, or just into a narrowing of the received bandwidth (which is
already narrowed down by the tight BC-453 85-kHz IF transformers). My
feeling is that said regenerative scheme would offer no advantage in
terms of image rejection, but I would value very much your opinion on
that subject.

73

Tony I0JX