Resistance Checking

[Scott Dorsey]

Chuck / KE4ETH > wrote:
>I have a question about checking resistance via chart in manual.
>
>A tube check good on a tubetester, but the resistance is way off from the
>chart. 5k ohms vs. 200k ohms. when the tube is pulled the pin measures about
>175k. all other pins check within 20-25k ohms on every tubes including the
>questionable tube.

What is this chart that you are using? Are you talking about measuring
resistances in-circuit with the manual for the equipment?

What is this pin?

>does this mean this tube is bad or only unusable for this application. It's
>the RF mixer in a Tempo one (the manual is packed, we had some floor
>replaced and I can't get to it at the moment.
>
>It's the first RF Mixer.

Does the mixer stage work? If the tube tests good and you are getting
signal at the IF strip, don't worry. If you aren't getting signal, something
is wrong, but if the in-circuit resistances are wrong it's probably not the
tube that is wrong.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Chuck / KE4ETH]

I have a question about checking resistance via chart in manual.

A tube check good on a tubetester, but the resistance is way off from the
chart. 5k ohms vs. 200k ohms. when the tube is pulled the pin measures about
175k. all other pins check within 20-25k ohms on every tubes including the
questionable tube.

does this mean this tube is bad or only unusable for this application. It's
the RF mixer in a Tempo one (the manual is packed, we had some floor
replaced and I can't get to it at the moment.

It's the first RF Mixer.

Thanks

Chuck

[Bill & Suzie Whatley]

You will get a more useful reply if you can give the identity of the tube.
( 6BA6, 12AU7, etc, etc.)

The resistance charts supplied with the older tube gear was usually measured
with the tubes still in the sockets.

73,

WA5VRL
Willis

[Ronald Oberloh]

Other than the filament pins and some really specialty tubes the tube
had better not have any effect on the resistance measurements and if it
does throw it as far as you can.

Bill & Suzie Whatley wrote:

>You will get a more useful reply if you can give the identity of the tube.
>( 6BA6, 12AU7, etc, etc.)
>
>The resistance charts supplied with the older tube gear was usually measured
>with the tubes still in the sockets.
>
>73,
>
>WA5VRL
>Willis
>
>
>
>
>

[--Bill--]

Ronald Oberloh wrote:
> Other than the filament pins and some really specialty tubes the tube
> had better not have any effect on the resistance measurements and if it
> does throw it as far as you can.

Its not too uncommon to have a grid with more than one pin connected.
On the socket there may be some components tagged off of one lug and
others off the other. Pulling the tube will break that continuity.

-Bill