Golborne Vintage Radio

Widlar and Gilbert, along with Bob Pease and Jim Williams were the original great IC designers. Only Gilbert is still alive.

Gilbert is pretty ancient - he's 80 - not much about him in the press in the last few years. One of my heroes - a real lateral thinker...

...and not as mad or as dangerous as Wilder...

Another thing that Gilbert was responsible for was the Tek 7000-series readout. Tek were ready to go with the same fibre-optic scheme they used in the 576 curve tracer, and even had four holes moulded in the top of the rear frame of the plugins, and mating holes in the edge connector mouldings in the mainframe.

Gilbert reckoned it was madness, so he built a character generator that wrote the readout onto the CRT screen mutiplexed with the trace. Out of discrete logic - probably a whole bucket load of TTL. He won the day, the implementation was then put onto custom chips, and that is what the entire 4-bay, and 3-bay 7000-series used.

The holes still remained however (and were a bit of a mystery unless you knew the history), right to the end of the 7000 series life. There was only one plugin that actually used them - for coax connections; that was the 7A21N direct access plugin. That is a highly specialised unit that connects the GR874 input sockets (+ and - differential, or single ended by rewiring coaxes) directly to the CRT vertical deflection plates. You have to physically move the y-amp backwards in the chassis, and then add passive boards that replaces the y-amp. Lousy sensitivity (4V/div single ended 10V/div differential, approx), but you get one hell of a bandwidth! 20kHz to >1GHz from a 7904.

I gave my 7904A and all it's plugins away after it developed the "click of death". Loved that 'scope - when I was a student doing my EE degree, I was sponsored by STL Harlow (part of ITT) so had to work for them for a few months a year - as a 19 y/o I had a 7000-series scope on my bench along with a tonne of other stuff.

My first bit of work with that was designing a digital filter for the Doppler MLS (Microwave Landing System) for Harrier jets.

I learnt to drive by pretending to be a Harrier - Honest!

We obviously couldn't afford to have a real Harrier hovering around for months while we were developing the system, so we had an LWB Landrover with approx. 1 million quids worth of electronics in the back...

...plus a huge controllable telescopic mast mounted behind the cab. On top of this we had our transducers - so I drove up and down this field for one Summer, raising and lowering the mast as we went and taking a billion measurements, pretending to be a Harrier taking off and landing.

Great fun. Harlow was a real dump, though...

(31-01-2017, 09:05 AM)Nick Wrote: [ -> ]I gave my 7904A and all it's plugins  away after it developed the "click of death". Loved that 'scope - when I was a student doing my EE degree, I was sponsored by STL Harlow (part of ITT) so had to work for them for a few months a year - as a 19 y/o I had a 7000-series scope on my bench along with a tonne of other stuff.

That was a really interesting post, Nick. I cut my design teeth on a system that I then installed in a trials cabin in Portsmouth. The cabin was roasting hot inside, chock full of electronics, and outside it was January - so ended up both boiling and freezing. That part of Portsmouth has as much to recommend it as Harlow 

Shame you gave the rather rare "A" version of the 7904 away. Goes like stink - mine goes up to well over 700MHz at -3dB with a 7A29 in it. The click of death from the power supply might just have been a response to a shorted tant somewhere in the mainframe or plugins.

Craig

It was more to do with space and reliability - most of my rather extensive Tek kit has now gone, including pretty much everything in the photo below (which was only a small part of the total)...

[attachment=15631]

Note: The 7904 was my normal 'scope after I passed on the 7904A, but then I moved onto the 2465A and the 7904 went too (as did the 2430A and a TDS224)...

Note #2: The small board that's under interrogation on the bench is my implementation of the famous Jim Williams ultra-low-distortion Wien-Bridge sine wave oscillator from Linear Tech AN43, figure 48...

Any progress in fixing the 'scope power supply, John?

Just read your posts lads from post 9 thanks for your input and stories love them, being a newbie this is a steep learning curve for me unfortunately old brain cells don't retain much.

Yes Craig, I joined the Tekscopes forum and the lads on there are helping.
I now have a trace but it's too bright.
No adjustment on intensity and very little on focus ie thick trace.
When turning Timebase clockwise high pitch frequency noise.
Voltages where
P115 = - 14.66vdc
P114 = + 14.75vdc
P112 = + 113.6vdc
P111 = + 247.8vdc
P113 = - 70vdc ???
PDF at Tek wiki if interested.
Many thanks
Any ideas most welcome.

The voltages look right (within typical errors), so your problem is not in the main power supply.

Suspect that U940 is questionable. Looking at the CRT Circuit and Calibrator (schematic 11) it says that the focus and intensity pots are ganged. Each of these connects to half of U940 (intensity to U940A and focus to U940B). So a duff U940 would explain a dim, unfocused trace that does not respond to focus/brightness.

U940 is a Tek custom chip 155-0051-00, alas

But you need to look at the signals shown to the left of the schematic to be sure what is wrong.

Sphere have these new at USD 40/ea and they're also available new on eBay...