Tube experts! - I T WORKS!

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sun Dec 5 14:03:40 1999

<Okay.. (my lack of tube knowledge talking)... a TV repair guy I know who us
<to do a lot of tube work told me tubes only last a couple of years. I did

In TVs where the tubes are low end and not always run at their best
operating points that may be true. In Qualtity test equipment that is
rarely the case.

<not want to have to recalibrate this scope everytime a tube drops out. Also
<I will be reselling quite a few of the tubescopes with PDP-8s and don't wan

Mechanical shock and power cycling tends to ruin tubes faster. Generally
tubes have good lifetimes and can be considered reliable (excluding the
effects of heat on surrounding parts) .

<the scopes going south a month after they get them. I've ordered the spare
<but first I'll see how long the scope will last with the ones it has now.

Best to leave be unless there is a direct indication one may be soft.
Don't forget with the exception of open filements or shorts from mechanical
shock tubes tend to fail slowly and soft.

<This one has 4 transistors in it. I am checking the caps right now.

Good idea s those (caps) do fail.

<>> The only reason I don't like tubes is because they are very flakey in ol
<>> mini computers.. From what I have heard from people who use to support
<them
<>> every power cycles was a nightmare. I am trying to stick to minis that
 
That is true, usually they get filiment failures and those are easy to
spot. Power cycles tend to accelerate that. then again I had a tube
organ (some 80+ tubes) and only had one failure in 8 years.

<>> 8/S.. I am going to put some highvoltage diodes between the 8/S,8I and
<>> scope to make sure if the scope goes bananas I don't blow a few hundred
<>> transistors in the minis.

???? 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.

Allison
Received on Sun Dec 05 1999 - 14:03:40 GMT