Next: The tunnel diode oscillator.

I have loads. You can't have any...

On a sunny day (Sat, 20 Jul 2013 13:02:55 -0700) it happened Fred Abse wrote in :

Oh yes I can: ebay.com 151 results for tunnel diode

Bye!

I have about 50, iirc. Not the really quick ones, which are up in the

Cheers

Phil Hobbs

If they were the best way to make an oscillator then they'd still be made.

In general they're interesting toys, unless you happen to be keeping equipment alive that uses them, or even are making equipment that just won't work without them (which latter case I find hard to believe...)

I have lots of TDs. I was digging through dusty bins at Haltek, and they had one box full. They didn't know what they were, so I bought a bunch for 10 cents each.

Here are a couple of TD manuals:

They have all sorts of fun circuits.

I used to build a lot of TD circuits when I was a kid, mostly switching stuff. My college senior project was "The Tunnel Diode Slideback Sampling Oscilloscope"

It's also fun to build a battery-powered 2-terminal negative resistor. Most common electronic equations work when you plug in negative resistance values.

Hey, we could do a negative frictional resistor, too. Put that in parallel with an LC and you'd get a linearly increasing envelope oscillation.

Haltek is gone, along with many other Silicon Valley surplus places.

That's what happens when you sell tunnel diodes for 10 cents.

On a sunny day (Sat, 20 Jul 2013 15:22:00 -0500) it happened Tim Wescott wrote in :

Yes, it was a practical problem, they had only 2 pins, and fell over all the time, while the 3 legged transistors stayed upright.

That's what happens when you provide the world with a convenient way to catalog-shop from surplus vendors all over. Because surplus vendors, more than a lot of other places, depend on serendipitous matches of stock with customer, being able to shop your stock to the widest variety of people is what's going to make the business work -- that used to mean being a surplus vendor in a physical spot with a lot of traffic of interested people. Now it means being good about having a good flexible online cataloging system, and a smart stock-jock who knows what he's selling.

There was another reason. I remember the Halted store here in town. From behind the counter they sold components at reasonable prices. But most of the store was full with old test equipment, floor to ceiling. And there was the problem, this stuff was IMHO totally overpriced. Sometimes easily 10x of what they charged at the next hamfest. So I never bought any of that.

Having cheap Chinese scopes, generators, power supplies, meters and whatnot did of course not help either.

Well, a lot of it was/is overpriced compared to hamfests (hamfest sales typically don't have anywhere near the overhead costs of store sales). Sometimes I've gotten lucky, though... got a 7S12 TDR/sampler plugin with an S-2 sampler head and an S-52 pulser for about $150, which seems to work just fine.

I think ebay is mostly to blame for killing off a lot of that stuff, flea markets and surplus stores. And around here, the cost of real estate priced places like Haltek off the market. Even Radio Shacks are getting rare.

from this page;

From the radioboard; "Putting "negative resistance" or "lambda diode" in Google Images brings a lot of examples and articles.

Here's a negative resistance created with FET and transistor. Shows a couple of oscillator circuits near bottom of page.

Tim Wescott schrieb:

In fact a lot of older Tek scopes (like my beloved ;-) 475) won't work without TDs as they are part of the trigger circuit.

Bye

Reinhard

I believe the shriveling up of Radio Shacks has another reason and it's also happening out here. Out of three stores withing 15mi we have one left. A few observations over the year:

a. Only the old guys in there really know where stuff is or what they have in terms of components. With younger ones that's the exception.

b. The folks I see buying parts, nuts and bolts are generally well over

c. Younger patrons just browse the cell phone offers and such. For that domain younger store clerks seem to know just about everything.

This was very different in the 80's. Back then I only came as a tourist but at least one Radio Shack visit was mandatory. You had you bag of parts and stood in line, behind other people with bags of parts and many of them young folks.

Yup. As I've mentioned before, the Radio Shack on Commonwealth Avenue in Boston was a big warehouse... hand in your parts list and a basket of parts came down a conveyer belt about 20 minutes later. ...Jim Thompson

I forgot which one but one of the places in Germany had tubes and tiny shuttle "Zeppelins" for that. Hand in your list, some time later ... weeeeeoooouuu ... *THWOCK* ... there were your parts.

Pity about the 811As. ;)

Pneumatic message tubes were seriously cool. They used to have them in one of the department stores my mum shopped at--all the credit card slips went straight to the accounting department.

Cheers

Phil Hobbs

They would have survived because those systems had fairly elaborate deceleration features at the ends of the tubes. The thwock noise came from the cover that flipped open after a shuttle arrived. In that store they were arranged so that the shuttles would not roll out of the tube by themselves, probably because they still sold tubes back then. Plus light bulbs, crystals, and so on.

In Germany I was told they were very common in single's bars. People could write little love notes to a person they saw at another table, dance requests and stuff. People said there was a constant whirring and hissing in the tubes under the ceiling and that some people gazed at that in amazement, wondering how it all worked without collisions.

That's interesting -- our local radio shack has mostly young clerks, with the occasional one that's astonishingly competent with the components (as often as not they're young women, which helps me with my electro-sexism).

But, that's probably because it's the closest Radio Shack to Clackamas Community College, which has a reasonably strong tech education department.

I think the main reason is that their components used to be decent-quality American, European, and Japanese stuff. No more. I can get real parts from real distributors in 2 days for $8 or so in shipping (Priority Mail). There's very little reason to go to Rat Shack for anything except in dire emergencies. (Despite the fact that there's one two blocks from my house.)

Cheers

Phil Hobbs