1. Must all the tubes be in socket to check DC. voltages from
bottom?? Some tubes are deeply burried in chasis and impossible to
measure from bottom. By removing tube and checking pin from top of
chasis - it would be possible to measure volts. Is this OK ?

2. I have no VTVM. Can a modern Fluke voltmeter be used ?

Thanks

James

On Thu, 17 Jun 2004 02:39:33 GMT, James wrote:

|1. Must all the tubes be in socket to check DC. voltages from
|bottom?? Some tubes are deeply burried in chasis and impossible to
|measure from bottom. By removing tube and checking pin from top of
|chasis - it would be possible to measure volts. Is this OK ?

Depends. If there is any resistance between the power supply and the
tube element(s) and the element draws current then the reading(s) will
be in error. For example a control grid in a class A stage will not
draw current and the voltage reading will be accurate. A screen grid
may or may not draw appreciable current thus the reading might be in
error.
|
|2. I have no VTVM. Can a modern Fluke voltmeter be used ?

Yes.

Wes N7WS

On Thu, 17 Jun 2004 02:39:33 GMT, James wrote:

1. Must all the tubes be in socket to check DC. voltages from
bottom?? Some tubes are deeply burried in chasis and impossible to
measure from bottom. By removing tube and checking pin from top of
chasis - it would be possible to measure volts. Is this OK ?

Some voltages will be absent or greatly changed with the tube
out-of-socket. To measure tube voltages from above the chassis with
the tube in place use tube socket test adaptors. I haven't seen any of
these for sale at a supplier or in a catalog in years, but they show
up on eBay and at antique radio meets and hamfests. Most of mine are
Pomona which I bought new many years ago. I like the Pomona adaptors
because you can easily connect mini-clips to their terminals.

Dale H. Cook, Chief Engineer, WWWR Roanoke VA, WCQV Moneta VA, WKBA
WZZI Vinton VA, WKPA WLNI WZZU Lynchburg VA, WMNA/WMNA-FM Gretna VA
http://members.cox.net/dalehcook/starcity.shtml

James wrote:
1. Must all the tubes be in socket to check DC. voltages from
bottom?? Some tubes are deeply burried in chasis and impossible to
measure from bottom. By removing tube and checking pin from top of
chasis - it would be possible to measure volts. Is this OK ?

No. Not at all. You can buy tube extenders that will allow you to measure
this stuff from the top of the chassis, though.

2. I have no VTVM. Can a modern Fluke voltmeter be used ?

Yes, if it has a high enough ohms-per-volt rating.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I'd like to add a caveat. Some older equipment, especially MIL gear may
well have been documented using either a 1000 or 20,000 Ohms/volt meter
such as the ME-9, PSM-6, et al. The book should say which kind of meter
should be used. If a VTVM is specified, of course the Fluke will do
very well.

1. Must all the tubes be in socket to check DC. voltages from
bottom?? Some tubes are deeply burried in chasis and impossible to
measure from bottom. By removing tube and checking pin from top of
chasis - it would be possible to measure volts. Is this OK ?

2. I have no VTVM. Can a modern Fluke voltmeter be used ?

Thanks

James

Tubes must be in for the correct voltages. Yes you can use the modern
meters for DC, but if you're measuring a radio the RF could cause
bogus readings and present a hazard. Do not rely on any digital meter
to give correct answers in a powered-on tube based boat anchor. You
can get nice meters (20kOhms/volt) for $10 from C&H or FairRadio. It
will be a lot safer.

Use the Fluke meter for static measurements and precision measurements.

Watch for tube test sockets at ham fairs. Or make your own. These
have pins that allow you to measure voltages with the tube plugged
in.
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA