Re: Sig gen and o-scopes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, October 26, 2002 9:25 PM
Subject: Sig gen and o-scopes


> Original poster: "John Richardson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jprich-at-up-dot-net>
>
> Hi,
>
> I recently watched TCBOR's Tesla Instrumentation video, and a signal
generator
> and o-scope seem like they would be good additions.  My question is
this-how
> many of you guys use them to find the resonant frequency of your coils,
and
> what should one look for in these units?  A quick e-bay search told me
that I
> could hook up with both for about 80 bucks.  In fact, the older units look
a
> lot simpler to operate than some of the more recent machines.  Should age
scare
> me if the units are in good working order?

Bear in mind that oscilloscopes have HV inside them, and unlike most other
electronics, HV stuff does age (the inevitable effect of microdischarge and
corona).  HV diodes fail, potting gets leaky, etc.

But, the real issue is the CRT.  An old scope might (will) have an old CRT
which may not have any life left in the cathode.  The primary life
determining thing in a CRT is the cathode, the emission of which gradually
decreases over life, reducing the beam current (i.e. the spot brightness).
Fortunately, oscilloscopes tend to run their CRTs conservatively, so you DO
get good life (compared to, say a computer monitor, often designed for a
life of 2000-3000 hrs (to half brightness)).

In any case, getting a replacement CRT could cost more than the scope.  Just
something to check out.

There are some nice web pages out there discussing the various Tek models,
the gotchas, and surveys of what you should be paying.


Also, would I be limited as to the
> availability of a high voltage probe for an old tube style scope?

Nope.. the probes all have BNC outputs, and any decent scope (in your
frequency range) will have a BNC input.

 I don't
> think that I would need anything fancy to find frequency, but maybe it's
not
> important enough to warrant the money.
>

For this application, I wouldn't go with an old tube based signal
generator... get one of the inexpensive solid state units (you don't need
super duper distortion performance, for instance).  Even a 555 based pulser
like "Terry's tuner" is a good enough source to do this sort of tuning.