Re: {Collins} Difference between 75S-1 and 75S-3

Hmmmmmmmmmm - Functional difference..  On the most basic level - NONE!  They
are both receivers.  :-)

On a performance level - DAY & NIGHT.  The 75S-3 is so much better a
performer that you will not ever go back to the S-1.  Do not misunderstand,
the 75S-1 is a good (not great - but good) receiver - but the 75S-3 is so
much better.

On a more detailed level,
75S-1 w/ 10 tubes (stripping away the Xtal Cal, the injection and PTO Osc
and the PTO Cath follower leaves):
      RF Amp, 2 Mixers cascaded, 2 IF amps w/ Mech Fil. And either Product
or AM Detect/AGC rectifier combo and then one audio Amp.
      Thus, the basic receiver is 1 RF Amp, 2 Mixers, 2 IF amps w/ Mech Fil.
Loss and the detector and Audio amp
      Performance results from 7 stages, 3 of which have gains less than 1
-and then mechanical filter losses. 

      The 75S-1 has no notch filter, no variable BFO

75S-3 w/12 tubes
     The same stripping away with the 745S-3 gives another stage of IF gain
(now essentially 3) combined with notch filter and separate AGC rectifier
and two stages of Audio gain. The technical result is better gain
distribution, selectivity,  audio out and AGC performance

The results are dramatic.  It is often stated that the 75S-3 is the best of
the S-Line receivers and I agree. 
It has the variable VFO/Fixed BFO feature, Notch Filter (Aka Q-Multiplier)
and selectable AGC time constant (not found on the S-1).

While the 75S-3B/C is more "sophisticated with plug-in filters, it is with
the sacrifice of skirt selectivity.  In addition, the entire Gain
Distribution and AGC performance is somewhat less than the 75S-3 in my

I have attached the Sherwood Engineering Receiver Comparison Data (Highly
respected) for the S-3 and S-3B/C and while the filter rejection and dynamic
range may look better for the 3B/C, I can tell you that in use, the 3 will
win your heart hands down.

Make sure when you look for an S-3 that it has the CW mechanical filter.  It
was an option in the S-3.

I apologize to the list as I know that the file will not go through, but the
data is readily available at:

Have fun in your hunt!

Bill Carns, N7OTQ (Trustee K0CXX)
Past President, Collins Collectors Association
Founding Board, Collins Radio Heritage Group
Editor, Signal Magazine (Retired)
Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)

-----Original Message-----
From: Collins [] On
Behalf Of Brian Gieryk via Collins
Sent: Saturday, October 28, 2017 10:58 AM
To: collins@xxxxxxxxxxxxx
Subject: {Collins} Difference between 75S-1 and 75S-3

Apologies in advance, as I am new to the world of S line equipment (but not
radio in general, nor HF-80 equipment).

What is the functional difference between a 75S-1 and the 75S-3?

Thank you!


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