开云体育

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Craig Sawyers
Sent: Friday, June 15, 2018 10:12 PM
To: [email protected]
Subject: Re: [TekScopes] S6 Sampling Head Bridge Cavity Question

I see now that I have been stuck in an endless spiral of screw-ups

of

my own making. Fixing them has certainly kept me busy most of my

life.

But every once in a while I surprise myself by doing something

really

astounding (at least to me) and I think all this stuff I learned had

a purpose.

Dennis Tillman W7PF

Hey - don't beat yourself up Dennis. The head might not be bust, there
might still just be a duff connection.

You didn't do something really stupid, like me when I plugged a
harmonica connector one pin out on the power supply of my 577 curve
tracer (unplugged originally to find a dead tant). Blew up most of the
silicon in the thing.

I've now got it pretty much sorted, other than one remaining problem
with either the step generator or amplifier. Real nightmare to sort
out. Rather fortunately every piece of silicon was easily available,
and socketted - even the dual FETs, which are still made.

Craig

You could likely make one. You'd need something for an anvil, could
easily be made from a 4mm or so rod, put a handle on it. The "hammer"
part could be made from an automatic center punch with a different
punch part. They're made to be removed. You'd want a design that
curled the end of the rivet over.

Note that eyelets work best if they are either solid copper, or tinned
copper. I'm not sure that any other variety would even accept solder.
Also, you may have to drill out the hole a bit if you are trying to
get the same inside diameter. A third (and slightly fatal) problem is
that I can't see any way to make this work on multi-layer boards.
Double sided is the most. It could hold down lifting foil on a single
sided board, also.

A little lathe work (if you have one) and it might just come together.

Harvey

Hi Bruce,
I think what you really are asking is what I ask every time I am going down to Beaverton: "why can't the Country Store be open when it is convenient for me because I happen to be in the area."

I think the answer is obvious. The store loses money. Being open twice per month is all they need to satisfy their regular customers (Ex-Tek employees) and just about everybody else.

Tek isn't interested in dealing with walk-in traffic for lots of reasons:
1) There is no reason to be open more often. If you are there on one of those days you would see there is only a very small group of people waiting to go in and they are mostly Ex-Tek people. So there is no reason to add more hours.
2) It is expensive to be open. You need someone (two people actually) to keep an eye out for people stuffing their pockets with small parts that have significant value.
3) Walk-in customers are a pain in the ass. I know because I am one. I will automatically ask them to lower the price enough on something I want so I can buy it.
4) Online sales via Ebay or whatever else they use are more cost effective because they can list big ticket items there.

Dennis Tillman W7PF
"Quando Omni Flunkus Terra Retreatum"

-----Original Message-----
From: Bruce Lane Sent: Friday, June 15, 2018 8:26 AM

Fellow Tekkies,

I've gotten curious about the rhyme or reason to the RAMS store's
limited public hours (two Thursdays a month, less than half a day).

Thoughts on this?

Thanks much.

--
---
Bruce Lane, ARS KC7GR

kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)

-----Original Message-----
From: zenith5106 Sent: Friday, June 15, 2018 4:09 AM

On Thu, Jun 14, 2018 at 11:42 pm, Dennis Tillman W7PF wrote:

I have absolutely no idea how you tell when either of the two output
barrels are touching the substrate. The only way I think Tek did it
was by applying strobe signals and monitoring the output on the

center

conductor of the barrels. As I turned them I kept hoping for some
change in resistance between the center conductor of the barrel and
the 5 pins that go into the cavity. I never got a reading of any

kind.

In the end I failed to get any output at all from the head when I

was done. It was dead.

Dennis,
This from a Maintenance Note from June 74:
//S-6 SAMPLING HEAD INTERMITTENT OUTPUT
In the past the S-6 Sampling Head has had an Intermittent problem in
the Hybrid Bridge Circuit.
The center conductor of the 3mm connector on the front panel connects
directly to the bridge sub-strate via a mechanical spring loaded
plunger. The Intermittent output Is caused by the plunger. Norm Farmer
of the Rockvllle Service Center has suggested a field fix which
entails cleaning the plunger. When you re-Install the spring and
plunger make sure the plunger is free enough not to bind up when
pushed all the way Inside the center connector, yet not so free that
it will fall out when you turn the connector upside down. This
practice insures that the center connector makes good contact with the
plunger. The front 3mm connector will be the only one you probably
will have to be concerned about. You will need a wrench to remove the
3mm connector. You can do this by increasing the width slightly of a
3/16th open-ended wrench The 3mm connector spring and plunger are not
shown In the S-6 manual. The part number for the spring is 214-1072-
00, and the plunger Is PN 131-0632-00.//

/H?kan

-----Original Message-----
From: Craig Sawyers Sent: Friday, June 15, 2018 12:11 AM

I have absolutely no idea how you tell when either of the two output
barrels are touching the substrate. The only way I think Tek did it
was by applying strobe signals and monitoring the

output on

the center conductor of the barrels. As I turned them I kept hoping
for some change in resistance between the center conductor of the
barrel and the 5 pins that go into the cavity. I never got a

reading

of any kind. In the end I failed to get any output at all from the
head when I was done. It was

dead.

Dennis Tillman W7PF

How did you check for a change in resistance, Dennis?

Craig

Hey Renee, I was just reading on sci.electronics.design about transistors degrading over time when they get alot of reverse Vbe. Actually they were talking about exceeding the rating or the transistor but how is that rating determined ? They obviously test it destructively and don't take 20 years to do it. So I think it possible that it could degrade even if the rating is not exceeded. Looking at the circuit, it might have quite a negative spike in the base drive.

I tried to measure the rise time but I am not 100 % sure of the scope. (one of the reasons I want the 422 running). I am not sure of the geometry, as in \_\ vs. /_/. I also made no attempt to measure the fall time when the transistor turns on. The Miller effect causes the rapidly falling collector voltage to get to the base and fight the base current. It also increases whatever negative spike.

Hmmm, just thought of something, I could use the 422 to cop the waveform from the 422. Why not ? It's not like trying to tickle yourself. It works well enough (once I get that filter in that poofed on me) to take waveforms in itself. The only time I guess you couldn't is trying to view a waveform in the same vertical channel you're using. But conceivably in channel one you could view channel 2 and vice versa. I want in the power supply, there should be no problem. I have alot more confidence in the Tek than my elcheapo daily driver scope. Eventually I am going to end up with a 7000 series, I can smell it. I think I can talk my buddy out of the 7603 if I get his 7834 up to snuff. But he has been too busy to do anything so, oh well.

Turn off time is most important with an inductive load, but turn on time is also important. I already measured the saturation voltage and it is low enough, at least by my (hopefully accurate) math. Turn on time is not as critical of course with the inductive load, but it does matter.

The design may be flawed. (the hell you say !) It is possible that at higher input voltage when the regulation is kicked in more, that the forward base current drops. I dunno, but it doesn't seem to be turnoff time, it doesn't seem to be the saturation voltage, when else could this dissipation be happening ? Leakage when off ? Well I see maybe what, 50 volts there ? Even at 10 mA that's only 50 mW.

I might just wire in a pair of 2SD427s I THINK I got and I do have a heatsink. you might want to try that with the 2N3055s. All you need is a piece of metal, a drill and for 50 measly volts you can use wax paper for an insulator, or use 2 pieces of metal and don't worry about insulation for now. I happen to have a bunch of heat sinks around but you don't want a 1,200 cm^2 thing for the test because the 422 doesn't have that. In fact the 422 doesn't even have any vent holes. It was designed to be rugged. A Tek rep told me years ago he saw one that had gone down a hill in a car rolling and it looked much better than the car. I also read that someone had grabbed one and slammed it hard on a table repeatedly and there was no damage. If ruggedness was their goal I guess they wouldn't want a spill or a few raindrops destroying their masterpiece.

And it is a masterpiece. Madman Muntz would be proud. Other than the power supply it only has I think 49 transistors in the whole thing, 3 nuvistors and a couple HV regulator tube. I think that on top of good engineering, Tek has had better CRTs. I think they make their own. Check out :



when you have spare half hour. And I was 7 years old at that time.

Muntz was a TV maker who used so few tubes that other engineers said there is no way in hell it could work. He is said to have walked around the prototype department and just remove parts from the units until they quit working. I think wiki has a page on him.


.

Chuck

“If you need some evidence to back my assertions, grab any old bag of electrolytic capacitors that have been sitting on the shelf for years, and measure the capacitance. They will all measure at the nominal value... after years of being operated at the extremely low voltage of 0V. “

Not sure if you’re trying to be funny, or if you’re serious.

If you’re serious, I think your comparison is irrelevant. Unless a capacitor is in a working environment, coping with heating and cooling cycles, you cannot compare it to a shelf model, no matter what voltage. And statistically, throwing a single bag of old undocumented caps into the ring here, is irrelevant.

“I have just such a bag of nichicons from a project where I overbought the caps. This was back in the 1970's. They all still read 2200uf +/- 10%.”

In the best case, it just goes to prove that Nichicon is still the right choice, today.