[R-390] Voltage charts and socket extenders.

[David Wise]

Sorry for the subject change, but I can't
find the original email.

Roger Ruszkowski (sp?) recently posted an opinion
that voltage readings were (a) taken with the
tube out of the socket and (b) with a TS-505:

> From: Roger L Ruszkowski [mailto:rlruszkowski@raytheon.com]
>
> A. we did not advocate tube extenders.
> B. there were numbers in the TM.
> C. we had a TS505 meter.
>
> I think the meter was to measure the pins with
> no tube in the socket.

I don't know the TS-505.  Is it a VOM or a VTVM?

In the manual, paragraph 5.4.5.2 says:

"To avoid removing a subchasis when voltage is
to be measured...at a tube-socket pin that does not
have a test point, remove the tube and [emphasis mine]
*use a tube adapter with test points*."

Although Table 1-11 "Test Equipment Required"
mentions the AN/PSM-4 multimeter, I'm convinced
it was only used to measure resistance, and that
all voltages were supposed to be measured with the
USM-116 or ME-6D/U Electronic Multimeter, which I
presume is a 10Meg device.  I don't know the
AN/PSM-4's sensitivity, so I calculated circuit
loading in the high-impedance limiter and audio
circuits, for 1k/V, 10k/V, and 20k/V VOMs.  They
all yield expected readings that are somewhat
below to far below the chart, while a 10M load
always comes close.  Also, there are places where
a no-tube reading can be proven to differ drastically
from the chart. An example is the limiter cathodes
with the limiter turned off.  They are around
80V with the tube but 0V without.

Always use a VTVM to measure voltage at
high-impedance points, and read voltages
with the tube in place.

73,
Dave Wise