T/R switch

[jimmy]

I am setting up a Collins 75A4 and Johnson Desk KW. What should I use for the T/R switch? a dowkey or vacuum relay.Dow key I know about , the vacuum relay, I no nothing. I will need help. Thanks for looking, your comments would be appreciated.
Jimmy K5CSU
Honobia061960@hughes.net

[Pete, WA2CWA]

If both can handle the RF requirements (you didn't mention any relay model numbers), then both can work. An issue might arise if you require additional keying contacts to handle muting, lighting a sign, etc. In a pinch, even a knife switch would work.

[WQ9E]

Whatever you use has to be able to reliably handle the power from this (which can hit around 3KW PEP) at 100% modulation in the high power AM position  AND it must engage rapidly on make and provide delay on PTT release to avoid flashover.  The Desk KW manual covers this issue.

I use a 24 volt DC vacuum relay, it is powered by a transformer/rectifier/filter from the 120V AC supplied on transmit and the filter capacitor discharging through the relay provides the required slight delay on PTT release.

Make sure you lubricate the bearings in all 4 Desk KW fans and clean the dust out, particularly from the grid compartment fan screen in the RF deck.  These fans tend to expire from old age but proper cleaning and lubrication will keep them going as long as possible.  One of the pedestal fans in mine went up in smoke several years ago and I replaced both with external fans saving the second pedestal fan motor to use in the RF deck where size constraints preclude easy substitution.  The new external fans (Rotron Patriot) move more air, are much quieter, and allow the easy installation of a filter on the lower intake fan to reduce dust buildup on the RF deck intake.