[Collins] R-388 Y112

[Gerald]

On Sat, 2005-12-31 at 13:32 -0600, Stanley Adams wrote:
> Have not heard any responses yet.   I wonder if anyone has a spare xtal
> filter or has ever used another means of shaping the if band pass in place
> of 
> Y112 for the 51J series (R-388) radio.
> 
> Happy New to all on the list and may God bless us and our country 
> for this coming year.
> 
> Stan Adams
> W4SBA
> 
> 
> Al Parker and myself were mulling over the options that are there when the
> main xtal filter (Y112) is nolo-worko.
> 
> Short of finding another 500kc 8 kc filter what is a fellow to do?
> KIWA option is out of the picture.  Does anyone know or suggest a cheaper
> avenue?  Murata Ceramic filters only work up to a CF of 456, so I do not
> think that this will be of any help.
> 
> Where are all the experts here?
> 
> Merry Christmas and Happy Holidays to everyone.
> 
> 
> Stanley Adams
> Memphis
> 
When Y112 doesn't work, its just like the selectivity 0 position. It has
no effect and the IF transformers set the AM bandwidth of the receiver.
Y112 does NOT set the receiver bandwidth. Its NOT replaceable by a
"filter" its a single crystal that has a sharp series resonance and a
relatively sharp parallel resonance. The phasing capacitor of the
crystal filter circuit balances out of phase voltage with that passing
through the crystal to create a sharper notch and peak, suitable mostly
for CW, not SSB, that can be moved a little in frequency. The spacing
and the bandwidths of both notch and peak are affected by the
resistances switched into the circuit in the various crystal filter
switch position, but if you are looking for a mechanical or ceramic
filter shaped response from Y112 you are NEVER going to get it. It don't
work that way.

This is not a "modern" receiver circuit where the IF stages after the
filter are there only to give gain and the filter sets the receiver
selectivity. In this receiver the IF transformers, ALL of them set the
receiver selectivity. It has its good and its bad points and it does
work and the concept has worked since the day Armstrong invented the
superheterodyne receiver.

This single crystal filter has been known in "single signal" receivers
since the early 1940s as far as I can document in my library and I think
was introduced by National in the HRO receiver in the mid 1930s.

Its NOT a bandpass filter and it doesn't set the receiver pass band.

You could contact one of the crystal makers in previous posts, though
I'd suggest International Crystal Manufacturing and give them Collins
part number for Y112. They can make one, probably have the
specifications, but they will charge at least $20, maybe $40 for the
crystal. Before doing that, look in a WW2 vintage ARRL Handbook for the
description of how that filter works and be sure its not working.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer