I have trouble believing it was intentionally designed that way, as opposed to kludged into the calibration procedure after the fact with a straight face.

@@frankwales I think I agree.

Possibly. I was thinking the same.

Yeah but going through it from start to finish gives you the utmost confidence in your equipment rather than just relying some past mystery.

Excellent idea! Good luck!

(uninformed/unresearched opinion) They are probably overengineered to the point that if there's overvoltage, a crowbar circuit will insta-kill the supply and if there's undervoltage, it just shuts off and the limits are probably set to

I think this would be known as capacitive coupling

Not 100% sure, but I think it couples capacitively to the heatsink of the transistor, which is connected to its collector.

Just don't try it with HV caps in tube circuits :)

@@KeritechElectronics if you’re following along “you’re doing so at your own risk” 🤣

@@Mark_C1 true, it's essential to know what you're doing :)

It's adjusting capacitance. There's a parasitic capacitor with one plate being the transistor's case and the other plate being one side of the capacitor being bent. Bending the capacitor changes the spacing between the plates of this parasitic capacitor, which changes its capacitance. Things like this were sometimes semi-intentional by the analog gurus. Bob Pease wrote an article about how he discovered a discrete op amp worked only because a few femtofarads of capacitance between its two circuit boards provided positive feedback necessary to make it function. When competitors tried to reverse engineer the design to copy it, they failed because they didn't find that tiny parasitic capacitance the designer hid in plain sight.

No. They say only if it fails the performance checks (they have a whole long chapter on performance checking), or if you have changed a component.

its Tektronix

Sam Battle has done that already though :)

@@KeritechElectronics Ha ha ha ha. Furbies and gameboys ain't lab equipment (well maybe these days it might be so). But Sam does some excellent work and am looking forward to visiting him this year.

@@MrMaxeemum I mean a hell of a lot of old tube generators. That collection could rival Mr Carlson's collection of Tek scopes :)

Capacitance varies with the distance between two conductors. You typically adjust rise time and overshoot by adjusting capacitance in some way. In this case, there is a small capacitance between the outside foil on that capacitor and the heatsink on the collector of the output transistor that is amplifying the square wave. By moving the cap closer or farther from the heatsink you change this capacitance, which might be in a feedback circuit (I haven't looked a the schematic).

@@lwilton Thank you. that makes it clear to me. I'd never realize this could happen. But it sounds very logical.

I bought a little 4 channel Rigol for the Computer History Museum restoration team for less than that, and it was very capable, including Fourrier transform for watching the spectra.

Made in China is not a bad thing so long as you know it passed the brands quality standards. I used to work in the Automotive industry and worked all over China for many many car companies (we supplied equipment to them) I once got talking with someone high up in VW and they admitted it was more expensive to manufacture in China just because of the rejects. Brands earn their respect through quality inspection. VW Chinese partners (FAW / SAIC / JAC) used the exact same equipment, the exact same production lines and produced absolute garbage. Do not buy Chinese brands unless you are willing to accept the possibility of a bad product. They are getting better but the ethics are not there.

@@CuriousMarc Thanks for the suggestion, Marc, I'll have a look at some Rigols.

Probably not that bad. Except for tweaking the two caps you could probably do the calibration in about 10 minutes with practice and the right test setup, which HP would have had. Maybe a half hour for the whole calibration, which was likely a lot faster than these came off the production line.

Paul Falstad has a visualizing circuit simulator with lots of example circuits, one of which is a triangle to sine converter.

@@malloryworlton6359 I was intrigued by its accuracy as well and tried it in LTSpice, which worked nicely as well. It doesn't look as fun as Paul's simulation though.

In that case they used a musical instrument called a Theremin. Those were very popular in Hollywood for SF movies in the 1950s.

@@lwilton Actually I ended up Googling Forbidden Planet after that. While FP was the first movie to use an all-electronic soundtrack, a theremin was not apparently used for it. Instead it was apparently some sort of home-brew synthesizer. I'm familiar with theremins. I built a small one from a kit some years ago. If I ever wish to induce my gf to leave me, all I'd need to do is play the theremin for an extended period of time. lol.

No worry. It will just buff out.

@@CuriousMarc Well i got further with it it seems like it blew Q14 (one of the output transistors) and something on the power supply and also the 47Ohm (39ohm in my version) resistor got a big crack through it and turned into a 2MΩ one, i hope that prevented damaging the frequency generator brain board A1. The 25V (+ and -) rail are both current limiting, without the frequency generator part, so only the final amplfiier as the load. No transistors seem to have shorted, but i havent verified the diode drop voltages on most. most passives allign with the parts list except for a few cases of being a later revision. I hope that the frequency signal shaping board A1 is fine and just the power supply and the amplfiier board died.

@@CuriousMarc Update: figured out what is wrong with it, the signal shaping board A1 is fine, just the output stage got blown, i ordered replacements and we will see if it does work after what i did.

@@janno288 Excellent news! Good luck on your repair!

@@CuriousMarc Thanks a lot!

Surely an EMI would be more 'fun'!

EMI2001 of course...

@@kiltrash1 It’s a long time ago….but ISTR that you could get a better picture out if the 2001!

I think it is capacitive coupling between the cap and the collector of the transistor, which is connected to its heatsink.

@@CuriousMarc This is a variation on a "gimmick" capacitor, very common in ham radio gear. Typically though a gimmick is just a piece of wire that you bend closer or farther to another wire or component.