Tektronix leadless capacitors, 1967-style - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 23, 2020, 12:52:41 am
content: I've taken a picture of the 1S2 sampling section where there are leadless capacitors. These are called out on the schematic and they are visible to the naked eye. So I've attached a photo for your wonderment and admiration.This is why the embedded pellets in the 1S1 totally surprised me. I never knew, in the 20 years I've been playing with them, that the 1S1 had even more advanced components than the 1S2 despite being 1/4 the bandwidth. Like I said I never looked close enough at the bridge to ever notice that missing network.I guess someone must have figured out that at 1GHz embedded parts aren't necessary and even at 3.9GHz you don't need to go that far.The leadless caps are pretty interesting, just a chunk of dielectric with electrodes plated on.The schematic page is 158/174 in the PDF.http://w140.com/tekwiki/images/b/b9/070-0889-00.pdf

author: Gyro
author_rank: Super Contributor
timestamp: June 23, 2020, 09:31:32 am
content: I've seen them (probably bigger) in old UHF TV tuners and the like. Basically, take a ceramic disc capacitor, don't solder the leads on, and don't encapsulate it in brown cement. It gives you the lowest possible parasitic inductance... and reasonable mechanical properties.I never saw a square one, but you could get low value ceramics in small square plate format, so presumably same (lack of) process.P.S. It's useful to know that carbon composition resistors were still up to the job at those sort of frequencies, I always keep some in hanging around.

author: David Hess
author_rank: Super Contributor
timestamp: June 23, 2020, 02:21:18 pm
content: Tektronix continued to use those leadless capacitors in new designs like the 7000 series sampling plug-ins through the 1970s.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 24, 2020, 01:12:01 am
content: In the mid 1970s, NEC, LGT, & no doubt, others, used what were commonly called "chip capacitors" to tuneVHF solid state RF amplifiers.We pushed them round the board with toothpicks till we got the correct response (position was remarkably critical), then tacked them in place with solder.Imagine my surprise, when 30+ years later, I found myself doing the same thing, using capacitors no different from the ones back then.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 24, 2020, 02:23:35 am
content: Quote from: Gyro on June 23, 2020, 09:31:32 amThe real high-speed stuff happens at the diode and the narrow spikes it sends down the transmission line. But yeah from what I understand the fact that these resistors are made in bulk instead of a film they are less inductive.Quote from: David Hess on June 23, 2020, 02:21:18 pmDo you know anything about the pellet parts from the 1S1? I am still stunned by that, how I could have not even noticed all this time...Quote from: vk6zgo on June 24, 2020, 01:12:01 amOh yes, still done that way today... If you crack open a RF transistor you might find the same thing is done inside at a much tinier scale, except with "patches" instead of discrete parts. Just little spots of copper next to the transmission line and bond wires brought to the patch until I guess the return loss is good enough to ship.

author: David Hess
author_rank: Super Contributor
timestamp: June 24, 2020, 10:31:58 pm
content: Quote from: Alex Eisenhut on June 24, 2020, 02:23:35 amI only know about the 1S1 from what I have read online.