Re: Off Topic: Wanted Spectracom 8212 Chart Recorder Manual


Hi Ed,

Yes, if you connect all three windings together you do get about 67VAC (25VAC + 25VAC + 17VAC) but that is not 110VAC by any stretch. You have an intriguing idea if the plugin did actually plug into two backplane connectors. But it only plugs into one backplane connector on the rear.

But you got me thinking it must have a transformer in it to boost the (25VAC + 25VAC) to 110VAC even though the chart recorder takes up most of the double wide space, so I looked carefully and there is a very flat form factor transformer on one side. You have to remove the side cover to find it. So that is how they must be doing it. I bet they use the +/-33VDC or the +11VDC windings to power the rest of the unit

Dennis Tillman W7PF

Dennis Tillman W7PF

-----Original Message-----
From: [] On Behalf Of Ed
Breya via Groups.Io
Sent: Sunday, June 10, 2018 6:42 PM
Subject: Re: [TekScopes] Off Topic: Wanted Spectracom 8212 Chart
Recorder Manual

Dennis, remember the TM500 has AC power available inside by virtue of
the floating LV AC windings - two per slot, so two slots could give
four windings at 24V-30V (I forget the specs) each that could add up
to around 110-120V (especially if that's the only load) - probably
close enough. Or, a single winding through a small step-up transformer
could do it to. I presume the chart paper drive is one of those old-
school synchronous clock motors with built-in gearbox to get whatever
speed is needed. Those only take about 3W, as I recall.


Dennis Tillman W7PF
TekScopes Moderator

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