"Asimov" wrote in
:

"Tim Schwartz" bravely wrote to "All" (11 May 04 12:11:00)
--- on the heady topic of " HP-400D voltmeter"

Tim, not to name a brand but I've found the s.brite green plastic
scouring pads are great for cleaning tube pins. Just push the tube
pins into the pad a few times (one at a time) and it gets cleaned of
oxide without removing too much of the gold, silver, or whatever
contact enhancing metal coating is used.


TS From: Tim Schwartz
TS Peter,

TS I'd start by cleaning all of the tube pins, as they are likely to
TS have corrosion on them from sitting all these years. Clean the
range TS selector switch too. I suggest leaving the tube pins dry
(no contact TS treatment) after cleaning. Sometimes 400 grit (more
or less) TS sandpaper is the best way to clean tube pins.

TS Regards,
TS Tim Schwartz
TS Bristol Electronics


TS "Peter E. Orban" wrote:

Hi Everyone,

I picked up an old HP-400D voltmeter on a garage sale. Having
cleaned most of the grime away from the equipment (it must have set
in a basement for years) I plugged it in. The tubes all light up and
the power supply voltage is around spec, but the meter moves always
past its maximum in every range. The second amplifier chain, after
the attenuator, is oscillating at about 1MHz, that is what the meter
is showing.
What could be the cause of the oscillation? Bad tubes?
I am also thinking about bad ground connections, as if (I have to
check this) grounds are connected to solder lugs that are riveted to
the frame. There could be some corrosion at those rivets.

Only if they were loose.



Use an eraser,the kind for removing ink. TEK used to have a tube-pin
cleaning tool made from rubber-abrasive rod like the 'bullets' used for
Dremel Moto-Tools,with a small hole in one end.You push it onto the tube
pin,and rotate the abrasive rod.

You could also have bad electrolytics in the PS or decoupling.
--
Jim Yanik
jyanik-at-kua.net