DEC VR01-A Display Unit (AKA Tek RM503 oscilloscope)

Paxton Hoag innfoclassics at
Fri Feb 23 12:56:56 CST 2007

On 2/23/07, Charles H. Dickman <chd_1 at> wrote:
> I just got ahold of a Tek RM503 oscilloscope. According to some
> documents I have found DEC sold this as the VR01-A. This one is probably
> not from DEC. First, does anyone know if there were any modifications
> made to use it as a point plot scope? It looks like there was just a
> cable that connected to the Z-axis/crt grid input on the back.
> Second, this scope has differential amplifiers for both horizontal and
> vertical inputs. I can't get the amplifiers to balance and so for any
> setting more sensitive than .1v/cm I can't get the trace on the screen.
> This shouldn't be a problem for how I want to use the scope, but I would
> like to have it fully functional and calibrated.
> Digging around inside, I see that the bias voltages for the cathode
> followers are not the same and this throws the whole differential amp
> out of balance. It can be compensated for at low gains by using the
> POSITION knob. If there are any valve or Tek scope experts out there,
> they can contact me offline so I can ask some naive questions about tubes.
> -chuck

This yahoo group is your friend.

Nearly 3000 people that know a lot about old Tek scopes, including
some who probably built your 503. Hmm, that is a long time a go, at
least some who have worked on them.


Paxton Hoag
Astoria, OR

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