Tube experts! - I T WORKS!

From: Merle K. Peirce <>
Date: Sun Dec 5 22:12:48 1999

One vistor mentioned they just scrapped two old Sperry Univacs becsue
they didn't know anyone who would want them....

On Sun, 5 Dec 1999, Christian Fandt wrote:

> Upon the date 02:16 PM 12/5/99 -0500, John B said something like:
> >
> >
> >
> >-----Original Message-----
> >From: Allison J Parent <>
> -- snip --
> >>???? Why? The scope is an enclosed system that would be hard pressed to
> >>emit high voltages back into the system it's hooked to. It's not like the
> >>HP9100 in that respect. For the RM503 to do that the HV lead would have to
> >>fall on one of the input lines! As I remember the series 8 Display scopes
> >>were driven off a pair of D/As and some single bit output to blank the
> >>beam. If you have something different I'd like to hear about that.
> I agree with Allison. Without knowing exactly the mods done by DEC that you
> mention below, I'm still assuming the output of the D/As is connected right
> into the SO-239 style front panel input connectors. In that case, the input
> circuitry is isolated from any HV. The inputs go directly to the vertical
> and horizontal amplifier tube grids (the 6DJ8's) after passing thru their
> respective attenuator switch assemblies.
> >
> >Three D/As. 1 12 bit for x, 1 12 bit for y, and 1 3 bit for intensity. When
> >the transformer went in this RM503 it raised the regular voltages throughout
> >the scope to 500+ volts... in some places over 1000. That was present right
> Ouch. I hope bypass capacitors and some coupling caps haven't had their
> dielectric damaged. Most of the ceramic caps and poly caps have ratings of
> 500 and 600 volts DC respectively and 1KV is pushing or exceeding their
> surge voltage rating.
> >through to the input. I am protecting the D/A converters as I don't need the
> >PDPs taking major beatings in the future. All the supplies inside the scope
> >(-100,100,250,85,-3000 were going nuts). The other RM503 I have has the same
> >problem. I am going to put an isolation transformer on every RM503,RM560
> >scope I get to solve the problem ahead of time.
> The other one has same problem? Interesting coincidence or possibly a
> common failure mode of this scope. I *was* going to put a benchtop style
> 503 on my 'hunt for' list as it looks to be an excellent X-Y scope for my
> bench but I'll do some further thinking on that I guess.
> >
> >The 8 Display controllers have the intensity option :-) (for spacewars of
> >course). The AX08 (XR option) and the 34D (standard) had a 3 bit intensity
> >D/A output for the scope. The RM503s were modified by DEC for intensity
> >control.
> That manual you said you have, is it from DEC or Tek? I'm curious about the
> mods. If you have a vanilla Tek manual like I have you can see that there
> are a pair of binding posts on the back of the unit which may be labeled
> "CRT GRID" and "GND." The GRID connection goes directly to the CRT grid
> through a 0.001 mfd capacitor.
> Now if DEC has done some fancy stuff to the 'scope by intrusively
> interfacing the PDP8 display controller directly to the deflection
> amplifier circuits in some manner then yes, I'd be leery of potential
> damage to the PDP circuits. Same for the intensity modulation (aka Z-axis
> modulation) circuit.
> Regards, Chris
> -- --
> Christian Fandt, Electronic/Electrical Historian
> Jamestown, NY USA
> Member of Antique Wireless Association
> URL:

M. K. Peirce
Rhode Island Computer Museum, Inc.
215 Shady Lea Road,
North Kingstown, RI 02852

"Casta est qui nemo rogavit."
              - Ovid
Received on Sun Dec 05 1999 - 22:12:48 GMT

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:31:54 BST