I spent a couple of hours last night making a little probe compensation loop
for my R7844 out of a couple bnc connectors and a cannibalized comp loop
from the front of a TEK 7904 I parted out. It didn't work as well as just
sticking the probe into the BNC connector out from the square wave reference
oscillator of the R7844. I know TEK offered a bnc to compensation loop
adapter for the R7844 (haven't seen any available, though.)

What am I doing wrong? Does it matter if I just stick the probe into the bnc
without the loop? I was able to compensate the probe for a pretty square
output this way, using the highest output voltage setting on the oscillator,
but I'm just curious why my mickey-moused compensation loop was useless.

Also, although my output looked like a pretty square wave, it only displayed
the horizontal lines.... No vertical lines were visible on the swing from
peak to peak. Is this indicative of a fault, or am I just missing something
obvious? I am relative newcomer to scopes in general, and I've been slowly
acquiring plugins for my mainframe (which I rescued from the dumpster, along
with a TEK 7904, all without plugins.) So far, it looks like the power
supply is a little out of spec (the character generator output seems to
jitter vertically for a few minutes before finally stabalizing. I will recap
as many electrolytics as possible just because I figure a 30-plus year old
electrolytic is probably suspect. I have a nice supply of spare parts from
the 7904, as far as logic chips, transistors, etc.

So far, I probably spent about $100 in plugins (7A26, 7A18, 7B53A, 7B80)
and probes. The CRT seems fine, and for a dual beam 400Mhz scope, I guess I
don't have much into it, money wise. It is probably overkill for me, since
I'll only be doing audio band stuff, but I have fun playing around with it
for the moment. I probaly could have found a working 2000 series for a
little more than what I've got in my dumpster find, but I seem to be
developing an addiction to dumpster diving and tinkering.

Anyway, any thoughts on my rant are welcome.

Tod

"Tod Treganowan" wrote in
:

I spent a couple of hours last night making a little probe
compensation loop for my R7844 out of a couple bnc connectors and a
cannibalized comp loop from the front of a TEK 7904 I parted out. It
didn't work as well as just sticking the probe into the BNC connector
out from the square wave reference oscillator of the R7844. I know TEK
offered a bnc to compensation loop adapter for the R7844 (haven't seen
any available, though.)

They made a JACK for the probe tip to adapt to the BNC.It grounded the
outer ring of the probe tip,and had a pin socket for the signal tip.It's
not really necessary,though,just stick the tip into the center of the BNC.

Or do you mean a *current probe* adapter? That would be a heavy wire loop
with a 50 ohm resistor to ground.Preferably a metal film chip resistor.

What am I doing wrong? Does it matter if I just stick the probe into
the bnc without the loop?

You don't need a loop for a voltage probe,the loop was for current probes.

I was able to compensate the probe for a
pretty square output this way, using the highest output voltage
setting on the oscillator, but I'm just curious why my mickey-moused
compensation loop was useless.

Also, although my output looked like a pretty square wave, it only
displayed the horizontal lines.... No vertical lines were visible on
the swing from peak to peak. Is this indicative of a fault, or am I
just missing something obvious?

The cal signal rise time is too fast for that sweep speed to display.
It's no fault.

I am relative newcomer to scopes in
general, and I've been slowly acquiring plugins for my mainframe
(which I rescued from the dumpster, along with a TEK 7904, all without
plugins.) So far, it looks like the power supply is a little out of
spec (the character generator output seems to jitter vertically for a
few minutes before finally stabalizing. I will recap as many
electrolytics as possible just because I figure a 30-plus year old
electrolytic is probably suspect. I have a nice supply of spare parts
from the 7904, as far as logic chips, transistors, etc.

So far, I probably spent about $100 in plugins (7A26, 7A18, 7B53A,
7B80) and probes. The CRT seems fine, and for a dual beam 400Mhz
scope, I guess I don't have much into it, money wise. It is probably
overkill for me, since I'll only be doing audio band stuff, but I have
fun playing around with it for the moment. I probaly could have found
a working 2000 series for a little more than what I've got in my
dumpster find, but I seem to be developing an addiction to dumpster
diving and tinkering.

You are better off with the 7000 series scopes you have;the 7904 is one of
the best of the series.

Anyway, any thoughts on my rant are welcome.

Tod






--
Jim Yanik
jyanik
at
kua.net

Thanks, Jim. Its nice to know I haven't completely wasted my time! Let me
know if you ever need any parts. I may have some.

Tod


"Jim Yanik" wrote in message
.. .
"Tod Treganowan" wrote in
:

I spent a couple of hours last night making a little probe
compensation loop for my R7844 out of a couple bnc connectors and a
cannibalized comp loop from the front of a TEK 7904 I parted out. It
didn't work as well as just sticking the probe into the BNC connector
out from the square wave reference oscillator of the R7844. I know TEK
offered a bnc to compensation loop adapter for the R7844 (haven't seen
any available, though.)

They made a JACK for the probe tip to adapt to the BNC.It grounded the
outer ring of the probe tip,and had a pin socket for the signal tip.It's
not really necessary,though,just stick the tip into the center of the BNC.

Or do you mean a *current probe* adapter? That would be a heavy wire loop
with a 50 ohm resistor to ground.Preferably a metal film chip resistor.

What am I doing wrong? Does it matter if I just stick the probe into
the bnc without the loop?

You don't need a loop for a voltage probe,the loop was for current probes.

I was able to compensate the probe for a
pretty square output this way, using the highest output voltage
setting on the oscillator, but I'm just curious why my mickey-moused
compensation loop was useless.

Also, although my output looked like a pretty square wave, it only
displayed the horizontal lines.... No vertical lines were visible on
the swing from peak to peak. Is this indicative of a fault, or am I
just missing something obvious?

The cal signal rise time is too fast for that sweep speed to display.
It's no fault.

I am relative newcomer to scopes in
general, and I've been slowly acquiring plugins for my mainframe
(which I rescued from the dumpster, along with a TEK 7904, all without
plugins.) So far, it looks like the power supply is a little out of
spec (the character generator output seems to jitter vertically for a
few minutes before finally stabalizing. I will recap as many
electrolytics as possible just because I figure a 30-plus year old
electrolytic is probably suspect. I have a nice supply of spare parts
from the 7904, as far as logic chips, transistors, etc.

So far, I probably spent about $100 in plugins (7A26, 7A18, 7B53A,
7B80) and probes. The CRT seems fine, and for a dual beam 400Mhz
scope, I guess I don't have much into it, money wise. It is probably
overkill for me, since I'll only be doing audio band stuff, but I have
fun playing around with it for the moment. I probaly could have found
a working 2000 series for a little more than what I've got in my
dumpster find, but I seem to be developing an addiction to dumpster
diving and tinkering.

You are better off with the 7000 series scopes you have;the 7904 is one of
the best of the series.

Anyway, any thoughts on my rant are welcome.

Tod






--
Jim Yanik
jyanik
at
kua.net

Lionel wrote in
:

On Thu, 20 Apr 2006 09:41:19 -0400, "Tod Treganowan"
opined:

Also, although my output looked like a pretty square wave, it only
displayed the horizontal lines.... No vertical lines were visible on
the swing from peak to peak. Is this indicative of a fault, or am I
just missing something obvious?

That's exactly what a good, clean square wave should look like on a
CRO. It's definitely not a fault!

It depends on the rise time of the square wave;some TEK scopes had really
slow RT's,like the T900's,and you definitely could see the rise and fall of
the signal,even on those low BW scopes.

Also,if your scope has a long-persistence phosphor it may display the rise
and fall better.

--
Jim Yanik
jyanik
at
kua.net