[R-390] R-390A Design Improvements

[rbethman]

Tisha,

This is my philosophy in a nutshell!

You're starting with what WAS the Rolls Royce of its time.  A LOT of 
careful thought was put into the design of the cost reduction version of 
the R-390.

Yes, it meant that "some" areas no longer equaled the original.  
However, the design team worked closely with the Signal Corps to come up 
with an "acceptable" replacement.

We make "some" small changes in the periphery, but nothing really 
substantial.  The biggest reason is that the core elements are out of 
our league or re-engineering abilities.  These old girls are 
electro-mechanical marvels!  I would NEVER attempt to tamper with the 
gearing and cam actions that are the heart of them.

I have one audio deck that the previous owner replaced the audio 
transformer with one that puts out an 8 ohm audio signal to the rear 
terminal strip.  Good on him!  I knew him well.  He was a satellite 
communications engineer by profession.  Ham radio was his love of life.  
He passed away in 2002 quietly, in his ham shack.

I'm sure he was happy!  I miss visiting with him in his enclave!  He's 
the one that introduced me to the resistor in lieu of the ballast tube.

Bob - N0DGN

On 2/22/2011 12:38 PM, Tisha Hayes wrote:
> I don't think any one of us can challenge the collective wisdom of the
> entire Collins design team.
>
> There are areas in the receiver where maybe a little bit more attention
> could have been paid by some of the individual designers. Some include;
>
> AGC action and the "moment of silence"
> Audio response (fine for military standards but maybe a bit poor for some of
> us)
> Overdoing the entire "cost reduction" scheme
> Narrowing down the front end to improve the IP3
>
> If you want to put in a different AGC switch, new capacitor and rewire a bit
> you can come up with better AGC action (the way it should have been done).
>
> By changing some caps you can reduce THD (total harmonic distortion) and
> restore some frequency response to the audio.
>
> If you want to put a relay and tube at the mysterious blank plate on the
> audio deck, make a slight mod to one front panel switch stop you can restore
> squelch functionality like the original R-390 had.
>
> If you want to narrow down the IF stagger tuning and maybe add a roofing
> filter the radio may work a bit better on closely spaced signals.
>
> We are not talking about major reworks like replacing all of the tubes with
> transistors or rewinding coils in the RF stage.
>
> Progress forward may be in little steps, sometimes smaller than what many
> may appreciate.