Yep, I also have one of those General Radio trombone lines on my bench. Hardly ever use it but when you need it it is invaluable. I first learned about these when I was investigating metastable states of high speed flip flops. If you violate the setup time specs of a flip flop between clock and data pins you can get the output to go into a metastable state where the voltage hovers in the middle for a long time. You need a trombone line to fine tune the timing between data and clock pins in order to see it.
I did a presentation a couple of nights ago on the nanoVNA for my ham radio club. As resources for further information I recommended this channel (and w2aew). This video is another example of why I offered the recommendation. Well, for that reason and also because I said it was entertaining to watch. There was at least one more fan of the "retired guy in the garage with the dryer" in the audience--you could tell because he said the channel was great but wished "he'd change topics" because "he's been on a tool kick for the past few days." - grin
Many years ago I worked for a company that made NB FM transceivers and my job was to automate the development testing. One of the systems I created was designed to look for amplifier instabilities and one part of the system was a trombone that was used to change the phase angle of a open or short circuit (sometimes the trombone was to short for the lower frequencies) I automated the trombone by building a stepper motor driven linear drive jig. The system also tested the amplifier across all supply voltages, frequencies, output powers, frequency span, and temperatures. The system could then be left to do its job saving engineers days of testing and do a more thorough job, ie most engineers wouldn’t wait for the amp to cool back down to temp after each run, so their devices would gradually warm up in the oven and so not really be tested at the lowest temperatures and that is where my system would pick up most of the unexpected spuri.
General Radio: a surprisingly not well known extraordinary innovator of technology and manufacturing. I parted out old castoff GR stuff when I was a curious kid, that I now wish I had in my possession intact. I've got a GR Strobotac sitting on an old farm milk can in my front hall as just a kind of appreciative artifact of innovation that got us here that we now so totally forget and take for granted. I hadn't run into a GR trombone line yet, but I'll keep an eye out for one. I've always been intimidated by the math associated with Smith Charts but I ought to revisit that with fresh eyes and a bit more self confidence. Thanks for the fun and fascinating video.
@@nerdful1 I don't know for sure if mine works. I knew the guy that I bought it from at a hamfest and he was selling it at a hamfest as part of helping Vermont Technical College clear out some really old lab equipment. It's got a University of Vermont inspection tag on it. The dial drive has too much friction and not enough friction until you spin it back and forth a few times and then it's good. With all of my ADHD passions for old technology and distractions from hypercritical near freak parents insisting that I throw things out (it's my own fucking house that I live in alone and that I have owned for almost 30 years) I haven't yet powered up the Strobotac. I think that the time is coming. I'll have to look up the schematic to see if it looks like a good or bad idea to bring the AC power up gradually using a genuine original GR Variac. Most old circuitry prefers being brought out of dormancy that way but for some things you do bad things like stripping emissivity from filaments running them lit but not lit enough.
@@trevorlewis8515 I wouldn't worry about bringing it up slowly. Those aren't transmitting or high power tubes. Over the decades I've brought it up slowly a few times. On a Genrad Variac of course. I've thought of going through it someday. It just works. And with the power line calibration neon bulb features, I know I am on the pitchers mound.
@@nerdful1 thank you. I tend to be concerned about old electrolytic capacitors that grenade and spew corrosive stuff and sometimes the mere ballistic force destroys other components. But I haven't opened up my Strobotac yet. Good ol General Radio probably used oil caps anyways because General Radio built things intended to function long past the far side of the apocalypse. But I don't think that I have a cord or a connector that can be a 2 prong female connector that's small enough in diameter to fit into my Strobotac's physically recessed "female-ish" power inlet that has male pins within the physically recessed female-ish opening? I think that my Strobotac has some very non-mainstream sexuality going on at it's point where the Strobotac wants to "receive some sizzling juice" Any tips on what/where I can get a non-molded-in connector that can "get it on" fitting into my Strobotac? No cords with molded in connectors for the load end, please. They'd be so old that they'd be made of real rubber and they're more cracked than kinky nowadays. But seriously I welcome if someone has something like a Hubbell, etc. part number of an interconnection device that can "get it on" delivering some AC juice into my Strobotac. I'd so welcome a spec of a specific connector I can go find on eBay to be able to "get it on" fitting with and feeding AC into my Strobotac... I'd be very grateful
@@lo2740 I don't understand how you mean, the impedance is determined by the ratio between the inner diameter of the outer conductor and the outer diameter of the inner conductor. There are three sections to consider, the impedance of the fixed coax, the section where the trombone overlap with the fixed coax and the coax in the trombone. Assume both the inner and outer conductor of the trombone slides inside the fixed coax then the air gap in the variable overlap will be two wall thicknesses smaller than before and after, it will therefore have different impedance. Similar problems applies regardless of which tube slides inside the other. Maybe it is some very clever design or simply very thin walled tubes.
Yep, I also have one of those General Radio trombone lines on my bench. Hardly ever use it but when you need it it is invaluable. I first learned about these when I was investigating metastable states of high speed flip flops. If you violate the setup time specs of a flip flop between clock and data pins you can get the output to go into a metastable state where the voltage hovers in the middle for a long time. You need a trombone line to fine tune the timing between data and clock pins in order to see it.
This was an excellent demonstration as to why changing the coax length does not change the SWR on the line, as some hams think.
I did a presentation a couple of nights ago on the nanoVNA for my ham radio club. As resources for further information I recommended this channel (and w2aew). This video is another example of why I offered the recommendation. Well, for that reason and also because I said it was entertaining to watch.
There was at least one more fan of the "retired guy in the garage with the dryer" in the audience--you could tell because he said the channel was great but wished "he'd change topics" because "he's been on a tool kick for the past few days." - grin
We want more chip of the day and magic smoke!.
I used one in the 60s to phase combine yagis to produce circular polarisation at a UK NASA satellite tracking station.
I enjoyed this trombone more than any trombone I've experienced before.
Many years ago I worked for a company that made NB FM transceivers and my job was to automate the development testing. One of the systems I created was designed to look for amplifier instabilities and one part of the system was a trombone that was used to change the phase angle of a open or short circuit (sometimes the trombone was to short for the lower frequencies) I automated the trombone by building a stepper motor driven linear drive jig. The system also tested the amplifier across all supply voltages, frequencies, output powers, frequency span, and temperatures. The system could then be left to do its job saving engineers days of testing and do a more thorough job, ie most engineers wouldn’t wait for the amp to cool back down to temp after each run, so their devices would gradually warm up in the oven and so not really be tested at the lowest temperatures and that is where my system would pick up most of the unexpected spuri.
Found two in a surplus electronics store. Used to document metastability of flip-flops by slowly changing set-up times. Aw, the memories!....
I sometimes did that "trick" with precisely cut piece of coax - but the adjustable thing is very interesting. Thany You.
General Radio: a surprisingly not well known extraordinary innovator of technology and manufacturing. I parted out old castoff GR stuff when I was a curious kid, that I now wish I had in my possession intact. I've got a GR Strobotac sitting on an old farm milk can in my front hall as just a kind of appreciative artifact of innovation that got us here that we now so totally forget and take for granted. I hadn't run into a GR trombone line yet, but I'll keep an eye out for one. I've always been intimidated by the math associated with Smith Charts but I ought to revisit that with fresh eyes and a bit more self confidence. Thanks for the fun and fascinating video.
I bring out my strobotac every Halloween. And sometimes for a small engine. I should go through it. I have a spare tube, but need a reflector.
@@nerdful1 I don't know for sure if mine works. I knew the guy that I bought it from at a hamfest and he was selling it at a hamfest as part of helping Vermont Technical College clear out some really old lab equipment. It's got a University of Vermont inspection tag on it. The dial drive has too much friction and not enough friction until you spin it back and forth a few times and then it's good. With all of my ADHD passions for old technology and distractions from hypercritical near freak parents insisting that I throw things out (it's my own fucking house that I live in alone and that I have owned for almost 30 years) I haven't yet powered up the Strobotac. I think that the time is coming. I'll have to look up the schematic to see if it looks like a good or bad idea to bring the AC power up gradually using a genuine original GR Variac. Most old circuitry prefers being brought out of dormancy that way but for some things you do bad things like stripping emissivity from filaments running them lit but not lit enough.
@@trevorlewis8515
I wouldn't worry about bringing it up slowly. Those aren't transmitting or high power tubes.
Over the decades I've brought it up slowly a few times. On a Genrad Variac of course. I've thought of going through it someday. It just works. And with the power line calibration neon bulb features, I know I am on the pitchers mound.
@@nerdful1 thank you. I tend to be concerned about old electrolytic capacitors that grenade and spew corrosive stuff and sometimes the mere ballistic force destroys other components. But I haven't opened up my Strobotac yet. Good ol General Radio probably used oil caps anyways because General Radio built things intended to function long past the far side of the apocalypse. But I don't think that I have a cord or a connector that can be a 2 prong female connector that's small enough in diameter to fit into my Strobotac's physically recessed "female-ish" power inlet that has male pins within the physically recessed female-ish opening?
I think that my Strobotac has some very non-mainstream sexuality going on at it's point where the Strobotac wants to "receive some sizzling juice"
Any tips on what/where I can get a non-molded-in connector that can "get it on" fitting into my Strobotac?
No cords with molded in connectors for the load end, please. They'd be so old that they'd be made of real rubber and they're more cracked than kinky nowadays.
But seriously I welcome if someone has something like a Hubbell, etc. part number of an interconnection device that can "get it on" delivering some AC juice into my Strobotac.
I'd so welcome a spec of a specific connector I can go find on eBay to be able to "get it on" fitting with and feeding AC into my Strobotac...
I'd be very grateful
Commonly used with a shorted connector and a T as a notch filter, because you get a shorter unit for a given freqency.
Cool demo! Deeper understanding of the Smith Chart acquired. I dub the.........The Great Sachmo!
There is also something identical for laser light and THz frequencies (in optics). But it is just a linear stage and two mirrors. :D
I have some with GR Hermaphrodyte connectors. Andcusedcrhem for complex impedance measurement. I used it for time domain reflecteonity too.
Very cool!
I played both slide and valve trombone.
These things must have cost a pretty penny, doesn't immediately strike me as an "aliexpress makes these for 20 dollar" type of item.
The 8711C is an expensive bit of kit. One day I hope to own one.
czcams.com/video/Saob5r6nb_4/video.htmlsi=KjA652vBYEI0etHd
@@IMSAIGuy woah! Thank you for sharing that.
Great!
Very cool
tuba. I played the tuba. NOT the sousaphone.
Sound explanation!
I have two single ones (not double like yours) They can only vary about 20 cm, for 2m work too little range..
Don't blow it! Pretty interesting :)
How do it maintain constant impedance? Seams hard to do mechanically.
like a coax cable, constant distance between the core and the shield, which is not a problem here since it only moves along the longitudinal axis.
@@lo2740 I don't understand how you mean, the impedance is determined by the ratio between the inner diameter of the outer conductor and the outer diameter of the inner conductor. There are three sections to consider, the impedance of the fixed coax, the section where the trombone overlap with the fixed coax and the coax in the trombone.
Assume both the inner and outer conductor of the trombone slides inside the fixed coax then the air gap in the variable overlap will be two wall thicknesses smaller than before and after, it will therefore have different impedance. Similar problems applies regardless of which tube slides inside the other.
Maybe it is some very clever design or simply very thin walled tubes.