[GreenKeys] RTTY receiver noise immunity?

[Duncan Brown]

On 22-Apr-21 12:59, Roy Morgan wrote:
> Greenkeyers (and R-390A nuts),
>
> The R-390A had a squelch modification, presumably supplied as original in some units.  It was installed in the spaces provided for it on the If module, I think.  The major parts needed were one tube, and a low-current relay, and possibly a different mode switch for the front panel. (It may be that the normal mode switch has the needed contact but is normally held out of operation by the stop plate.). Maybe there was an added squelch level control added to the front panel, but my memory is faint on that point.
>
> Very likely there is a modification document that tells about this.
>
> The relay needed has a coil of about 10,000 ohms resistance and is operated by the roughly 10 milliamp plate circuit of the associated 12AU7 (?) tube.  Such relays can be bought currently for $100 or more, thought they likely are not the sealed military grade as the originals were.  My security contractor seriously advises me to neither confirm nor deny that I have any such relays.
>
The R-392 (little brother of the R-390) had a squelch control. I thought 
the R-390 did also, but looking at the front panel of one, I don't see 
it.  Maybe I saw one (~50 years ago) with Roy's mod somewhere.

Have fun,

Duncan
K2OEQ