Re: Tektronix 7104 Available


Hi Steve,
Yes, I was referring to "production scopes", and more specifically to
"conventional analog production scopes". Few people other than you would
know of the few, exotic, exceptions that exceeded the 1GHz limit. I am aware
of scopes other than you cited that exceeded the 1GHz bandwidth but as you
point out they can be quite strange due to the engineering constraints
reality imposes at that frequency.

For example B&H Engineering in Yonkers NY modified the 7104 to push it to
3GHz. They were able to do this because the incredible MCP CRT of the 7104
has a 3dB deflection point in excess of 3GHz (this is documented in the 7104
Service manual). The vertical system of the 7104 was completely removed by
B&H and they developed a single ended 3GHz vertical plugin based on a DC to
3GHz module they designed (which had over 20% ringing at some frequencies).

This vertical amplifier had to bypass the interface connector on the back of
the plugin via SMB connectors that were mounted in 2 of the 4 holes at the
top of the shroud on the rear of the plugin. Once past the interface, I
believe the vertical signal was mated directly to the 7104 delay line. Only
one CRT deflection plate was driven. I have two different B&H vertical
plugins (one has a variable delay line and the other does not) but I have
yet to find a B&H mainframe. As far as I know their scope relied on Tek 7B10
and 7B15 time bases which were not modified so this scope would have had
trouble triggering at anything beyond what those time bases are capable of.

It may seem like the 3GHz capability of the 7104 MCP CRT would make it
possible for Tek to have built an even faster 7104 but that was not the case
for many reasons: The 7000 series was not designed for it and the cost would
be prohibitive to adapt it to higher frequencies; Digital scopes were
catching up rapidly; The low cost dedicated scopes were taking their toll on
the more expensive general purpose laboratory scopes like the 7000.

I don't believe that the 519 has better linearity than the 7104. I haven't
done a test personally although I briefly had a 519 in my home. It wasn't
mine so I didn't dare turn it on for fear that I might damage it. I use the
7104 extensively and have never noticed a single anomaly when compared to 3
7603s, a 7844, 7854, or 7934. John Addis and Bruce Hofer at Tek were issued
US patent 4132958 for the Feedbeside Compensation circuit that corrects the
amplifiers of the 7104 for thermals which is what I think you are referring

I have seen a 519 working at the VintageTEK museum and it would be virtually
impossible to measure linearity on that tiny 2cm x 6cm screen accurately
enough to compare it to the 7cm x 9cm of the 7104. If you can get a more
precise definition of what the EG&G folks were referring to by 'linearity' I
think we can persuade the folks at the museum to do a direct comparison of
the 519 to the 7104 and take some 'linearity' measurements.


-----Original Message-----
From: Steve
Sent: Wednesday, March 27, 2013 1:17 PM

--- In, "Dennis Tillman" <dennis@...> wrote:

The 7104 that Dick is selling is the fastest analog scope ever made.
By coincidence I took this CRT photo on mine yesterday which will give
you an idea of what it is capable of. This is a 2GHz 350mV signal
displayed on the
7104 with the identical plugins that Dick has in his 7104. The 7104 is
spec'd at 1GHz. The gain at 2GHz is down by about 9X but there it is
triggering and the waveform is clear as a bell.

You need to qualify that statement a bit. The 7104 is the fastest
production conventional analog scope ever made. Key qualifiers: Production
and Conventional.

The former Soviet Union built scopes for government use that were faster.
As with their scan converter digitizers, the CRTs were very long (well over
a meter), allowing low deflection angles. These were custom built and not
sold outside of a few government labs. I have never seen one, but have
heard accounts directly from former users. They did not have microchannel
plates, so cameras were needed for single shot capture. The amplifiers were
not DC coupled.

Iwatsu had a couple of models of scan converter based "analog scopes" that
were faster as well. These are funny animals - in one sense they act like
an analog scope, but the display is digital. No memory, and conventional
scope trigger only (no view of the pre-triggered portion of the waveform).
But they have color LCD displays with unique colors for each channel's
trace. The scan converter requires much less deflection angle than a
conventional human viewed CRT, the target being only a couple of millimeters
high. Hence the exotic amplifier chain used in the 7104 is not required to
drive it. They are still fast amplifiers however.

I believe Iwatsu made these through the late 1990s.

The Tek 519 also has 1 GHz BW, but is direct access (input drives the CRT,
having no amplifiers) and weird deflection factors like 1.37 V/cm. The
calibrated area of the CRT is only 2 divisions high, one on either side of
ground. While these restrictions are very limiting, I have heard from users
at EG&G that it actually has better vertical linearity that the 7104. I
have never seen a working 519 and can not verify that statement, but I
remember hearing that the linearity and thermal compensation in the 7104 are
not as good as in other Tek lab scopes. Some tradeoffs needed to be made to
design this wonderful scope.



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