Some oscilloscope pictures

Poor planning ?

Sylvia Else wrote: ==============

There are two 111k resistors ( for each X plate) in parallel plus the "trick capacitor" in a feedback path to the base of a BF119. Likely purpose is frequency compensation for a bit of L in the Rs. Sometimes you see two plastic coated wires gently twisted for the same job.

...... Phil

No, not sure why I misread that.

t.>

Sylvia.

It's a gimmick capacitor, a twisted pair variable cap.

I showed one of my young engineers how to do that last week. We didn't yet have the code to drive a digital variable capacitor, so she couldn't tune an oscillator to within phaselock range, so that was a temporary fix to let us test her FPGA phaselock code.

On a sunny day (Mon, 23 Aug 2021 12:30:08 +1000) it happened Sylvia Else snipped-for-privacy@email.invalid wrote in snipped-for-privacy@mid.individual.net>:

Thin wires mains side? Kept away from sensitive electronics on other board?

When I worked for Tek we calibrated the V amp to the CRT by bending the wires to the CRT, that changed C and the frequency response needed to be within some limit. This insulated wire, if bended, does the same Maybe the is also some inductor in there?

It is a gimmick capacitor, often made with a couple of wires twisted together to make a ~1pF fiddlable capacitor.

Quite a lot of old Tektronix equipment relied on parasitic stray capacitance and inductance of circuit tracks. They had the decency to include the caps on the schematics, and to indicate they couldn't be seen on the boards.

It's not the positioning I'm questioning, but the mode of attachment. There are plenty of wire-to-board connectors available, and that would surely have made assembly easier.

It would certainly have made repair easier, though they probably didn't care about that. The transistor I have to replace is at the edge of the board, and can be desoldered and resoldered, albeit with some fiddling.

If I had to replace something closer to the middle of the board [*], I'd have to unsolder all the soldered wires, and somehow hope to be able to reconnect them later - perhaps by installing the wire-to-board connectors the thing should have had in the first place.

Sylvia.

On a sunny day (Mon, 23 Aug 2021 17:04:41 +1000) it happened Sylvia Else snipped-for-privacy@email.invalid wrote in snipped-for-privacy@mid.individual.net>:

Yes, but that may degrade the soldering on the board side.. Not easy to service this thing, same for my old Trio scope, although that is a bit better accessible. Sometimes it helps before taking apart such a wire labyrinth to take a few pictures so you at least get the colors of the wires right... Cameras are a great help.

OTOH the less connectors the less problems :-)

=================

Recently had to replace a pair of 5 leg, dual transistors in an old Sansui home amp ( AU5900 ) Saved about 2 hours time and a lot of grief by snipping off the device itself off leaving 5 x 1cm leads behind.

..... Phil

Sylvia Else wrote: =============

--------------------------------------------------- That power tranny is a regular E-Core with no magnetic shielding or even a copper flux shorting strap.

Surprising it does not cause some trembling of the trace - being so close to the CRT like that.

..... Phil

They also discovered "hook", the terrible time-domain behavior of FR4 as a capacitor.

We did one NMR gradient amp with two power transformers, where proper placement and phasing made the fields cancel where it mattered.

It is impressive how much stuff is inside an old analog scope. A cheap

Multi-channel traces never worked well in analog scopes. They shared the tube with alternate traces, or chopped.

Digital scopes often share ADCs, which costs sample rate when additional channels are enabled. For dual trace, it's better to use 2 and 3, instead of the obvious 1 and 2.

Indeed, but they also used the "tricks" where that wasn't important, e.g. time-domain calibrators where the (nuvistor's) output is a sinewave.

I acquired a dual /beam/ analogue storage scope before it hit the dumpster. After replacing the usual PSU electrolytics, it still works as well as analogue storage scopes ever did.

Dual beam is particularly useful with a dual channel storage scope, since ALT mode is pretty useless at capturing fast transients, and CHOP is only useful at low speeds.

Must sell it sometime.

The giant Tek with the separate power supply?

Analog storage never worked well. The secondary-emission tubes wore out. The mesh things had low writing rates. All primitive.

We have a 7104, the 1 GHz microchannel scope, but we don't use it any more. That display shuts off about once a minute to extend tube life. Nuisance.

It's distributed deflection, sort of like these, but ceramic so you can't see inside:

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OTOH:

My 50Mhz, dual trace is a steel box 90% full of air. Has to be deep enough to accommodate the PDA tube = 14 inches. The front panel has to fit all the controls comfortably = 10 x 7 inches. Easy to carry in one hand and uses only 14 watts of power. No need for a stupid, dust clogging fan.

Purchased on the 19/9/1985. Never out of use.

...... Phil

John Larkin wrote: ==============

Plus it's no more than 10% of the volume and barely affects the weight .

.... Phil