Date   

Re: oh yeah?

 

Hi Snapdiode,

I really prefer to keep my head low and I do not like to discuss what Tek stuff I am lucky to own but I thought it would give you some perspective. I have accumulated one (or more) of everything relating to the 7000 series (except the mainframes which I don't have room for) because I do a lot of very different things in electronics and I hate it when I don't have the right plugin or accessory that I need to see the signal I am curious about. This is how I learn. So all this equipment gives me an almost infinite ability to explore any aspect of electronics that catches my curiosity. Most of the time I forget about what I have. When I saw your post I became curious about just how many heads I had. Honestly, I was pretty surprised when I stacked them all up. The only reason I have the S-1, S-2, S-3A, and S-5 is because they complete the set. I can't say I've ever used them because the S-4 is much faster. I use the S-4 for fast pulse measurement and the S-6 for TDR stuff a lot .

I haven't found a tool that can remove those nuts on the back of the S-42. Even with a narrow needle nose that space is so tight it takes about 5 minutes to turn one off an 1/8th of a turn at a time. Why they didn’t use long screws with the heads sticking out the back is beyond me. All the other S-xx heads are easy in comparison.

Dennis

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of snapdiode via Groups.Io
Sent: Monday, August 12, 2019 4:10 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] oh yeah?

So I sent my crown back to the jeweler's.

Is there a specific key for removing the nuts holding the S-42 together or should I try to use my mini-Wescott? It's really cramped there.




--
Dennis Tillman W7PF
TekScopes Moderator


Looking for another complete P6201 FET Probe

Sean Turner
 

Hi all,

Some time back I got extraordinarily lucky and scored a basically brand new and unused P6201 (complete with box, all accessories, and with inspection tags still attached) for a killer price (under $200, a lot of ebay sellers seem to thing they can put insane prices on just the probe with NO accessories...) Have given up hope of finding another like that on ebay. Wondering if anyone here might have one they'd let go. I would prefer complete. I am shopping so I can populate both 7A29 amplifiers on my 7104.

Please feel free to contact me privately.

Thanks,

Sean


Re: 5xx 'Scopes

Dave Seiter
 

I wish they wouldn't advertise how many tubes are inside, it's almost a lure for tube harvesters.
-Dave

On Monday, August 12, 2019, 05:29:49 PM PDT, sdturne@q.com <sdturne@q.com> wrote:

On Mon, Aug 12, 2019 at 05:22 PM, Paul Amaranth wrote:


Here's a couple on the Detroit Craigslist:
https://detroit.craigslist.org/okl/ele/d/farmington-oscilloscope-tektronix-545/6952136679.html

No affiliation, yada yada.

Paul
I wish I was closer...those look nice.

Sean


Re: 5xx 'Scopes

Dave Seiter
 

There always seem to be some near the SF bay area: 
sacramento for sale "tektronix -wanted" - craigslist
But the prices tend to be silly.  What I don't understand is people who try and sell a 555 and it's PS separately; I guess it's possible to have one and need the other.  I wonder if they have a cable?  Maybe they don't and that's why they are separate- no they say the 555 "powers up".
-Dave


Re: 5xx 'Scopes

Sean Turner
 

On Mon, Aug 12, 2019 at 05:22 PM, Paul Amaranth wrote:


Here's a couple on the Detroit Craigslist:
https://detroit.craigslist.org/okl/ele/d/farmington-oscilloscope-tektronix-545/6952136679.html

No affiliation, yada yada.

Paul
I wish I was closer...those look nice.

Sean


Re: 5xx 'Scopes

Sean Turner
 

On Mon, Aug 12, 2019 at 04:07 PM, Morris Odell wrote:


The ultimate in heating is to compare the standard frequency outputs of two HP
524 series vacuum tube counters in a 555. There are almost 300 tubes glowing
at the same time and four fans circulating the warmth.

It's a cold winter in the southern end of Australia so I'm tempted to try it
again but electricity is getting very expensive down here..

Morris
I can see the heat shimmer from here...no need for no stinkin' Yule log...everyone huddle around the test equipment!

Sean


Re: 5xx 'Scopes

Paul Amaranth
 

Here's a couple on the Detroit Craigslist:
https://detroit.craigslist.org/okl/ele/d/farmington-oscilloscope-tektronix-545/6952136679.html

No affiliation, yada yada.

Paul

On Tue, Aug 13, 2019 at 12:05:02AM +0000, John Griessen wrote:
On 8/12/19 6:07 PM, Morris Odell wrote:
The ultimate in heating is to compare the standard frequency outputs of two HP 524 series vacuum tube counters in a 555. There are almost 300 tubes glowing at the same time and four fans circulating the warmth.

It's a cold winter in the southern end of Australia so I'm tempted to try it again but electricity is getting very expensive down here..
If you go solar PV panels, it would be winter daytime heating and entertaining at the same time :-)
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix & Windows


Re: 5xx 'Scopes

John Griessen
 

On 8/12/19 6:07 PM, Morris Odell wrote:
The ultimate in heating is to compare the standard frequency outputs of two HP 524 series vacuum tube counters in a 555. There are almost 300 tubes glowing at the same time and four fans circulating the warmth.
It's a cold winter in the southern end of Australia so I'm tempted to try it again but electricity is getting very expensive down here..
If you go solar PV panels, it would be winter daytime heating and entertaining at the same time :-)


Re: 5xx 'Scopes

Leanna L Erickson <lle@...>
 

I have two working 524s.

Keith
Wayzata, mn

On Aug 12, 2019, at 6:07 PM, Morris Odell <vilgotch1@gmail.com> wrote:

The king of heating is a single Beam, the Tek 517.
The ultimate in heating is to compare the standard frequency outputs of two HP 524 series vacuum tube counters in a 555. There are almost 300 tubes glowing at the same time and four fans circulating the warmth.

It's a cold winter in the southern end of Australia so I'm tempted to try it again but electricity is getting very expensive down here..

Morris



Re: General Radio 874 Connector, inner conductor "bendies"

Dave Seiter
 

Hi Dennis,
Yes, the inner conductor for the 125ohm version is considerably smaller than the normal version.  I've always wondered if there was another use for them because some of the people selling them think they are made from pure gold (apparently).  The box that's on ebay now has been there since at least 2008.  When I was actively looking for them, they were easy to spot from far away at swap meets due to the gold.  If there was a bin of 874s, I always did a quick scan of all of them because just as you occasionally run across a "normal" 874 that is gold plated, I have found 125 ohm versions that are not gold plated.  (I have a "T" connector sitting on the couch next to me which has no gold at all, even though all three ends are 125 ohm).   Also, the oldest 519 I have has no gold plated connectors at all.  Seems odd to use gold plating as a visual key, but I guess if you're buying a 519, it's nice to have some bling instead of colored plastic.
-Dave

On Monday, August 12, 2019, 09:40:29 AM PDT, Dennis Tillman W7PF <dennis@ridesoft.com> wrote:

Hi Dave,
If I remember correctly the reason for the 125 ohm connectors was because that was the impedance of the vertical deflection plates. The input signal went directly to the plates. So I would guess the answer is no - there was no other use for 125 ohm connectors

To get 125 ohm characteristic impedance the size of the inner conductor has to be different than for a 50 ohm characteristic impedance so Tek made special 50 ohm to 125 ohm adapters. The 50 ohm GR 874 connector was on one end and the 125 ohm GR connector was at the other end. The 50 ohm end was the standard color of all GR connectors. The 125 ohm end was plated with gold. Because of the gold they were quite eye catching and "unique". The entire set of adapters Tek made for the 519 came in a really beautiful mahogany box. I had one of those boxes with most of the 519 adapters. The box,  the adapters, and the 519 are now in Barrie Gilbert's collection of scopes.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dave Seiter
Sent: Monday, August 12, 2019 9:03 AM

Speaking of the 874 connectors, were the 125 ohm versions ever used for anything unrelated to the 519s, or by anyone outside of Tek?
-Dave


On Sunday, August 11, 2019, 05:12:44 PM PDT, Dale H. Cook <bridgewaterma@plymouthcolony.net> wrote:

On 8/11/2019 4:08 PM, Bruce Hunter  wrote:

The 774-series connectors were the predecessors of the 874-type and best described as a banana plug encased with an outer shield.  They were not hermaphroditic.


--
Dennis Tillman W7PF
TekScopes Moderator


Re: P6249 Oscillation

Lawrance A. Schneider
 

Hi,

Perchance a silly question, but as a fellow fizzilist, how long is the ground lead? Maybe a resnoant problem?

On Aug 12, 2019, at 1:36 PM, wjlentz@gmail.com wrote:

4 P6249 probes passed through my hands that have 1 MHz oscillation. On one probe, this oscillation only shows up after a 5 minute warmup. The oscillation can be as large as 467 millivolts on one probe which makes it mostly useless. On another probe the oscillation is smaller and manageable. The probes that have oscillation meet rise-time specs and have no dc offset. I have one very expensive P6249 probe that has no hint of oscillation.

I have two TDS 694C 3 GHz oscilloscopes and needed an active probe with higher impedance than my 500 ohm passive probes. The TDS 694C is wired to power the P6249 4 GHz probe with +/-5V and +/-15 supplies and a data and clock pin interface to the TDAS694C.. I have the Tek manual which only shows a block schematic for the part that connects at the oscilloscope but not what is actually in the active probe tip. The oscillation shows up on all eight of the inputs for the two TDS 694C scopes I have.

Is there any information about what is in the probe tip such as a schematic? Is there any way to open the sealed probe tip? Would reducing the +/- voltage to the probe tip at the scope connection, which can be opened, help the problem?
All I hear from repair places is that they do not work on this probe. Local sources of the probes are asking more for the probe than I paid for my TDS 694C scopes.

I have the 1 GHz and 1.5 GHz versions of the probe which do not use the +/- 15V supply and have no hint of oscillation, but I do need the bandwidth for my photon counting business.
www.marinaphotonics.com.
I designed the PV16 1.5 GHz 65db gain amplifier discriminator for my photon counter which is in a 29mm cube and does not oscillate, so I have some knowledge of electronics. At this point I admit that I am just stubborn and want to fix the probe problem rather than go to another probe.
Jerry the fizzilist
PS that's what happens to physicists when they get older




Re: oh yeah?

snapdiode
 

So I sent my crown back to the jeweler's.

Is there a specific key for removing the nuts holding the S-42 together or should I try to use my mini-Wescott? It's really cramped there.


Re: 5xx 'Scopes

Morris Odell
 

The king of heating is a single Beam, the Tek 517.
The ultimate in heating is to compare the standard frequency outputs of two HP 524 series vacuum tube counters in a 555. There are almost 300 tubes glowing at the same time and four fans circulating the warmth.

It's a cold winter in the southern end of Australia so I'm tempted to try it again but electricity is getting very expensive down here..

Morris


Re: oh yeah?

fiftythreebuick <ae5i@...>
 

Hi Dennis-

If you EVER find a good way to adapt anything standard into a 7F10, please let me know! I have searched and searched with no results at all. It's like everything with those doggone connectors on it had been swallowed up by the earth! Wouldn't an adaptor be nice? :-)

Best of luck to us both!

Tom

On Mon, Aug 12, 2019 at 09:47 AM, Dennis Tillman W7PF wrote:


<text removed>


But my 7F10, which was designed in the mid-1980s when there were still no
standardized fiber connectors, uses a Diamond 3.5mm connector. So it isn't
compatible with anything I have. I believe the Diamond connectors are so
obsolete that nobody makes them anymore and everyone seems to have thrown out
any fibers they had that used it. I have searched in vain for an adapter
/converter that would have an FC/PC on one end and a Diamond 3.5mm on the
other.

It was possible to order the 7F10 with a different connector that was in use
back in the 1980s so it should be possible to pop open the Optical to
Electrical Converter front end and connect a fiber pig-tail to it that has an
FC/PC on it but I don't have the tools or the expertise to do that.

At this point the 7F10 is the only 7000 plugin I own that I can't use. That
really annoys me. It does respond when I hold a fiber up to its connector and
shine it in just right.

Dennis W7PF


Re: 7B90P: What makes the buttons work?

 

Of all people I should realize the incredible depth of knowledge in this
group. When am I going to learn???
Instead I spend hours wasting time trying to figure things out when others
are way ahead of me.

Holger Lubben sent me part of the answer. Holger has DUPLICATED the very
complex and very rare 021-0374-00 GPIB Decoder plugin for the 7000. This was
a massive undertaking which astonished me when I heard about it. His part of
the answer comes from page 5 and 6 of the manual for the 021-0374-00. It
says that the 8.5V Zener diode VR330 has to be replaced with a 7.5V Zener.
Holger also said the 7B90P would only work in a 7854. That is correct if you
want to program it via GPIB using the 021-0374-00 but I discovered it works
perfectly fine in any scope as long as you are able to do what Chris says in
his reply (provided you replace the Zener).

Brian Skilton provided me with the other half of the answer. The +5V
lighting supply has to be turned all the way up to High. This switch is
usually on the back of the scope off to one side or the other side of the
power supply.

After I replaced the Zener and turned up the light supply the 7B90P worked
perfectly in a 7934 Storage scope.
NOTE: I already added the shorting plug across P028 which is locates on the
sweep circuit board close to the edge connector.

I have two other 7B90Ps I will try to get working this afternoon.
Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Brian
via Groups.Io
Sent: Monday, August 12, 2019 11:38 AM

Hi Dennis , You wont have seen much from me on this group as I usually have
little to add to any conversations but :--The jumpers you refer to if I
recall correctly dont enable anything as such , what they do is to parallel
the dontrol illumination supply with the normal slot supply for 5 volts as
the modules overload the 5 v supply . To make this work the illumination
control needs to be set to maximum or it will add nothing to the normal
supply . As a test bed for the ones I have I added a 5v 2A supply and
connected it to the illumination supply connections , in the 7313 there are
no illuminated controls so it sits there quite happily until needed .I hope
this info helps in some way

Brian Skilton

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
cmjones01
Sent: Monday, August 12, 2019 1:05 PM

On Mon, 12 Aug 2019, 20:21 Dennis Tillman W7PF, <dennis@ridesoft.com> wrote:
Has anyone figured out how to get the 7B90P to respond to its front panel
buttons?
I have a 7B90P which lives in my 7912AD. As Brian has said, these plugins
run their logic (including the microprocessor) from the +5V lighting supply,
so they don't work at all if that supply is missing (like in the 3-bay
mainframes) or low (like in 4-bay mainframes with the lighting set to dim).
I've used the 7B90P in 7704A, 7904A and 7912AD mainframes and it works fine
as long as that lighting supply is there and at 'full brightness'.

I've got the paper manual for the 7B90P. The design is pretty neat: the
microprocessor is actually halted unless it's processing a key press or GPIB
command, so it doesn't create any unnecessary noise.

Chris

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dennis
Tillman W7PF
Sent: Monday, August 12, 2019 11:21 AM
To: TekScopes@groups.io
Subject: [TekScopes] 7B90P: What makes the buttons work?

Tek made four programmable plugins for the 7000 series. They are the 7A16P
and 7A29P vertical amplifiers, and the 7B81P and 7B90P time bases. The 7B81P
never went into production.

These were intended for the digitizing 7000 mainframes. But for calibration
purposes they have to be able to work in standard 7K mainframes.

So all of these programmable plugins have a jumper next to the rear
interface connector that activates the front pushbuttons. By placing a small
shorting plug across the two pins at the rear, the front panel pushbuttons
are activated.



The only exception is the 7B90P. It has the jumper but the plugin seems to
be waiting for something else as well.

I have tried shorting out all of the possible locations on the 7B90P that
might also be involved but I haven't found the secret to making the front
panel work.

The preliminary manual (that is all there is as far as I know) is no help.



Has anyone figured out how to get the 7B90P to respond to its front panel
buttons?



Dennis Tillman W7PF






--
Dennis Tillman W7PF
TekScopes Moderator


Re: Is an early 7A26 a keeper?

 

Hi John,
Chuck makes a good point but there are exceptions.

A few years ago I was testing an exclusive OR integrated circuit which, no matter what I tried, would not go faster than 99MHz. I was using the very fastest TTL logic families (AS, ALS, FAST, etc) and the delay times and all of the datasheet parameters said it should run as fast as the gates in the rest of the family I was using). The rest of the logic had no problem running at 150MHz with the careful PCB layout I created and all the bypass caps I used.

The IC has 1nSec rise and fall times and gate delays of a few nSec so it is very fast. To find out what was causing this I wired four XOR gates together in such a way that there was always a normal pulse going into one input of the test XOR and an identical (in time) but inverted pulse going into the other XOR input of the test gate. To monitor the original pulse from the pulse generator, and the inverted pulse and the output of the XOR required that I connect four 100X 5K P6057 probes to the circuit with bayonet grounding tips (to minimize ground bounce. It is impossible to do that. You need 4 or 5 hands. But you understand the idea.

I needed a practical solution. The 50ohm X100 probe did not load the gates of the IC but I couldn't hold everything together and press the bayonet pin into a good ground to minimize ground bounce and see what was causing the XOR to fail at 99MHz. It was essential that I get it working at 100MHz. The rest of the circuit was working at 150MHz.

The solution came when I stumbled across a web page where the author showed how easy it was to make your own 5K X100 probes that could be soldered in place. That completely eliminated the ground bounce, the rise times were flawless and the problem ultimately turned out to be the clever internal design of the XOR. It turns out every logic family uses the same circuit design for an XOR. It was invented a very long time ago and it is so clever and so fast that it is a no brainer. But at very high frequencies there is a race condition that causes it to fail. Every XOR I tried from every TTL family would not go faster than 99MHz. But I got beautiful scope pictures of the failure showing how it worked up to 99MHz and after that it would always put out a glitch.

That is an example where you must have a 100X 50ohm probe (actually three of them) and in my case it made a huge difference that I could solder my homemade probes right to the pins of the IC and to the ground plane next to the IC.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Monday, August 12, 2019 2:20 PM

I suppose the question you should ask yourself is:

What kinds of RF circuits can stand to be probed with a
50 ohm probe?

In my experience, most 50 ohm inputs on equipment is intended to be connected by coax to 50 ohm outputs.

When a probe is used on a plugin like the 7A24, it is generally an active probe, such as a FET probe. The FET does the conversion between high impedance, low capacitive loading probing, and the 50 ohm input on the plugin.

-Chuck Harris

John wrote:>
..
This is a little off topic but I'll ask anyway. I have a 7A24 dual trace 50 ohm input impedance vertical plugin. I also have a P6201 active FET probe. Is there any point for me trying to locate at a reasonable price (current eBay prices are looney tunes) a P6034 or P6056 50 ohm passive probe? I mainly work in VHF and UHF. Currently I'm doing fine without it so that may just be the answer. What am I missing by not having a passive low impedance probe?

John
VK2DLP



--
Dennis Tillman W7PF
TekScopes Moderator


Re: Is an early 7A26 a keeper?

 

Hi John,
I have seen this 1/2 amplitude before myself so I know it is not uncommon. Unfortunately I don't remember the cause at the moment but I'm sure somebody else will be able to say what is causing it. I would suggest looking carefully at the gold fingers in the attenuator. It may be that the attenuator that does the divide by two is constantly in circuit because the gold contact fingers that are normally pressed down to make contact as necessary by the drum switch are actually touching down on the PC board all the time so that divide by 2 attenuator is always in circuit.

Your other question is easier to answer: The low impedance of a 50 ohm probe allows it to have a very wide bandwidth. For instance the P6034 is good to above 3.5GHz, the P6035 is good to above 1.7GHz, the P6056 has a rise time of 0.1nSec (equivalent to a 3.5GHz BW), and the P6057 is a 1.7GHz probe. The capacitive loading (which is frequency dependent) on a circuit using one of these probes is very low (1pF or less).

The 7A24 in a fast mainframe is good to at least 400MHz so you won't benefit too much from one of those probes. But if you ever get a 7A29 1GHz amplifier then you will need a 50 ohm X10 or X100 probe to check UHF circuits with.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of John
Sent: Monday, August 12, 2019 2:02 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Is an early 7A26 a keeper?

I have a early 7A26 that has had the upgrade done to it. Serial B086310. The ECO was basically to replace the vertical amplifier micro circuits and was applied to serial numbers between B010100 and B139377. The ECO was numbered 040-0785-01 and included modifications M24099, M34167, S35105. This 7A26 has a problem with channel 1 with the deflection being almost exactly 1/2 that of channel 2. Everything else looks good on it and I suspect U1350. I have another working 7A26 so this one is waiting for time (on my part) to go in and fix it. I have a bit too much on my plate at the moment so time is a commodity in scarce supply (isn't it always?). When it gets fixed I will have a 4 channel 250 MHz vertical section for my 7934A mainframe.

This is a little off topic but I'll ask anyway. I have a 7A24 dual trace 50 ohm input impedance vertical plugin. I also have a P6201 active FET probe. Is there any point for me trying to locate at a reasonable price (current eBay prices are looney tunes) a P6034 or P6056 50 ohm passive probe? I mainly work in VHF and UHF. Currently I'm doing fine without it so that may just be the answer. What am I missing by not having a passive low impedance probe?

John
VK2DLP





--
Dennis Tillman W7PF
TekScopes Moderator


Re: Is an early 7A26 a keeper?

Chuck Harris <cfharris@...>
 

I suppose the question you should ask yourself is:

What kinds of RF circuits can stand to be probed with a
50 ohm probe?

In my experience, most 50 ohm inputs on equipment is
intended to be connected by coax to 50 ohm outputs.

When a probe is used on a plugin like the 7A24, it is
generally an active probe, such as a FET probe. The FET
does the conversion between high impedance, low capacitive
loading probing, and the 50 ohm input on the plugin.

-Chuck Harris

John wrote:>
...

This is a little off topic but I'll ask anyway. I have a 7A24 dual trace 50 ohm input impedance vertical plugin. I also have a P6201 active FET probe. Is there any point for me trying to locate at a reasonable price (current eBay prices are looney tunes) a P6034 or P6056 50 ohm passive probe? I mainly work in VHF and UHF. Currently I'm doing fine without it so that may just be the answer. What am I missing by not having a passive low impedance probe?

John
VK2DLP




Re: Is an early 7A26 a keeper?

John
 

I have a early 7A26 that has had the upgrade done to it. Serial B086310. The ECO was basically to replace the vertical amplifier micro circuits and was applied to serial numbers between B010100 and B139377. The ECO was numbered 040-0785-01 and included modifications M24099, M34167, S35105. This 7A26 has a problem with channel 1 with the deflection being almost exactly 1/2 that of channel 2. Everything else looks good on it and I suspect U1350. I have another working 7A26 so this one is waiting for time (on my part) to go in and fix it. I have a bit too much on my plate at the moment so time is a commodity in scarce supply (isn't it always?). When it gets fixed I will have a 4 channel 250 MHz vertical section for my 7934A mainframe.

This is a little off topic but I'll ask anyway. I have a 7A24 dual trace 50 ohm input impedance vertical plugin. I also have a P6201 active FET probe. Is there any point for me trying to locate at a reasonable price (current eBay prices are looney tunes) a P6034 or P6056 50 ohm passive probe? I mainly work in VHF and UHF. Currently I'm doing fine without it so that may just be the answer. What am I missing by not having a passive low impedance probe?

John
VK2DLP


Re: 7B90P: What makes the buttons work?

cmjones01
 

On Mon, 12 Aug 2019, 20:21 Dennis Tillman W7PF, <dennis@ridesoft.com> wrote:



Has anyone figured out how to get the 7B90P to respond to its front panel
buttons?
I have a 7B90P which lives in my 7912AD. As Brian has said, these plugins
run their logic (including the microprocessor) from the +5V lighting
supply, so they don't work at all if that supply is missing (like in the
3-bay mainframes) or low (like in 4-bay mainframes with the lighting set to
dim). I've used the 7B90P in 7704A, 7904A and 7912AD mainframes and it
works fine as long as that lighting supply is there and at 'full
brightness'.

I've got the paper manual for the 7B90P. The design is pretty neat: the
microprocessor is actually halted unless it's processing a key press or
GPIB command, so it doesn't create any unnecessary noise.

Chris

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