There must have been a good reason
I think all 28 ASR and many (most?) versions of 28KSR and 28RO have a line relay and internal loop used to key the selector magnets. Some instead have transistor or tube SMD.
My theory is that an ASR can have things like an aux reperf and who-knows-what-else in it, so they thought it best to have a local loop supply, lest they bog-down the external supply with too many widgets in the cabinet. Whereas the KSR doesn't have other gadgets and can be driven right from the external loop. Just my thoughts on the matter.
Right now, I am using an ST-6 for a loop supply (and also for 170 shift) but mine is of the newer ilk that doesn't have a rheostat, only a fixed power resistor. I now find my loop running at about 50mA due to a lot of devices on the loop.
73 Eugene W2HX
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-----Original Message-----
From: greenkeys-bounces@mailman.qth.net <greenkeys-bounces@mailman.qth.net> On Behalf Of John W9DDD
Sent: Sunday, February 5, 2023 10:22 PM
To: harold@w6iwi.org
Cc: greenkeys@mailman.qth.net
Subject: Re: [GreenKeys] Range Finder Setting/Distortion usage?
2874WD and 2875WD show a 28 KSR without line (polar) relay. I have not yet found a diagram for an ASR without the line relay, but when I do, my ASR will also be without the relay.
John,