Test Equipment Anonymous (TEA) group therapy thread

[VK5RC]

👍😁

[bd139]

Well those are not real LM741s. The 741 has a gain bandwidth of about 1.5MHz. Amplitude is also limited by the slew rate of 0.5V/us.
No way are you getting a gain of 1 out of a 741 at 10MHz.
Also have you loaded the output? should really be able to drive 50R. A old composite video amplifier works well especially if you put a ethernet isolating transfoumer / balun on the outputs. The Extro ones ae very nice. A VGA one with BNCs will also work.

LM7171 has 200Mhz unity-gain bandwidth. In simulation I was able to get 150Mhz easy.

For the transfo I think I saw in the spec something like 2db attenuation. I need to check back.

 
I read 741, not 7171 some kind of mental abberation or confirmation bias   
The 7171 is good for this.

That sort of mis-cognition results from having too many people around of which you know with a high degree of certainty that upon hearing OPA they will by default propose their blasted 741/324/2904 abominations like none other, and far nicer ones existed.
IMO they should be relegated to the same category like coal mine ponies, flintlocks, slate tablets....

Nothing wrong with them if you know where not to use ‘em. And they are sooooo cheap. I got a whole tube of new 358’s for less than a pint in a London pub  . They’re cheap enough to throw on the carpet if someone you dislike is coming over

[0culus]

Best way to fix an oscillator - make a high gain amp - it will be an oscillator - well that is what happens for me! (and vice versa)!

Who needs high gain - my last "successful" oscillator creation was supposed to be a unity gain 'diamond transistor' output stage!

How does that joke go? "Amplifiers oscillate and oscillators don't" 

[0culus]

BTW, preemptive note: I will be otherwise occupied this weekend and will not be on discord.

[mnementh]

I'll be... somewhere. Doing... something. I may even be conscious, but I can't promise anything. 

mnem
 

[Neomys Sapiens]

Well those are not real LM741s. The 741 has a gain bandwidth of about 1.5MHz. Amplitude is also limited by the slew rate of 0.5V/us.
No way are you getting a gain of 1 out of a 741 at 10MHz.
Also have you loaded the output? should really be able to drive 50R. A old composite video amplifier works well especially if you put a ethernet isolating transfoumer / balun on the outputs. The Extro ones ae very nice. A VGA one with BNCs will also work.

LM7171 has 200Mhz unity-gain bandwidth. In simulation I was able to get 150Mhz easy.

For the transfo I think I saw in the spec something like 2db attenuation. I need to check back.

 
I read 741, not 7171 some kind of mental abberation or confirmation bias   
The 7171 is good for this.

That sort of mis-cognition results from having too many people around of which you know with a high degree of certainty that upon hearing OPA they will by default propose their blasted 741/324/2904 abominations like none other, and far nicer ones existed.
IMO they should be relegated to the same category like coal mine ponies, flintlocks, slate tablets....

Nothing wrong with them if you know where not to use ‘em. And they are sooooo cheap. I got a whole tube of new 358’s for less than a pint in a London pub  . They’re cheap enough to throw on the carpet if someone you dislike is coming over

I totally expected you to chime in in defense of those components.
But now I am having further thoughts regarding the deeper reasons behind. I start to wonder if there are such things as 'instability fetishism', 'non-linearity fanciers', and related deviations.

Let's pretend I'm a 741 and you are a 1MHz square wave?

[med6753]

BTW, preemptive note: I will be otherwise occupied this weekend and will not be on discord.

I probably won't be on either. The Lady Cop is coming up Friday evening and I'll take her home Monday afternoon.

[0culus]

Have fun! 

Ken Shirriff has another interesting blog. Larry Bower, the designer of the ca 1974 -hp- "Nanoprocessor" 1820-1691, kept the original photolithography masks and has released them. If you have a way to manipulate Photoshop files, you can download it and explore!

http://www.righto.com/2020/09/inside-hp-nanoprocessor-high-speed.html?m=1

[bitseeker]

As someone who likes to wear T-Shirts I wanted to have one with a TEA logo on it.
But I wasn't able to find such a logo, perhaps I've overlooked it somehow.

If we don't have a TEA logo, is there somebody here with us with some
graphical and artist talents (and is willing to do) who could create such a logo?

My abilites in this respect are fairly mediocre.

Any ideas, how such a TEA logo should look alike?

I've contemplated, off and on, about having T-shirts made. Of course, that requires a logo to start with. I created a TEA YouTube channel, just in case, but since we don't have a logo, I just put a good ol' CRO instead.

The ideas for either a logo or a t-shirt design so far are quite fun to see. Keep 'em coming. And the two are not mutually exclusive. For example, the logo could go on the front in the "pocket" area and a full design on the back. I'd definitely want to have them silk-screened. No thermal transfer rubbish! So, that'd probably require a batch run.

A logo idea that's been bouncing around in my head for a while is a tea cup with a DMM in it. It can be kept clean and simple (bd139 is spot on there), which is important for many reasons including clarity at various sizes and robustness across different media including embroidery where too much detail fails and too many colors gets really expensive. Interesting to see that Mnem's TEA dragon illustration is mighty similar.

I also like bd's retro concept with that vintage Tek logo mod.

So, keep the ideas flowing. Maybe this weekend I'll try to create the logo that's in my head and see if it looks better, as good as, or terribly worse than I imagine.

[bitseeker]

I have mine... y'all can do WTF-ever you like with yours. 

LOL! Good one, mnem. I was thinking similarly, both graphically and spelling. In the spelling department, I was considering grabbing the domain for some time. Now that the idea is kind of "out there," I pulled the trigger so some squatter doesn't beat me to it.

http://teanonymous.com

It currently redirects here. Convenient shortcut.

[bitseeker]

Here's a quick mashup using existing artwork from the interwebs.

[Neomys Sapiens]

Nice to see that a significant proportion of us has a life besides TEA.
(I just assume it's nothing boring or negative)
So do I, recently. Still open regarding the Discord meet, though.

[bitseeker]

Discord's always open...better than a pub.

Now, it's off to bed for me. One more day of work.

[capt bullshot]

Well I opened a claim last night, I mentioned the damage, poor packaging* and added lots of pictures.
Got a stupid reply this morning

whats wrong with the items ? can u give us more details ? i will solve it for u

 
Sent the details again & pointed out previously added pictures, hopefully they will take notice this time as I can't escalate until the 11th.

*On the plus side they were individually bagged in glass shard containment zip-lock bags.

David

Ah, that's the usual beginning of the usual show. Be prepared to exchange quite a few messages with them, but just keep saying "these things are broken, I can't use them" and insist on a full refund, and tell them you're annoyed by their delays. The answers will get more and more hilarious

[Zucca]

We need also this on the Teashirt:



moreover I would suggest to leave the upper arm (left or right) free for the TEA name as a badge...

[tggzzz]

Heads up that I've just noticed an unexpected[1] message in my fleabay inbox with a £1 selling offer. 

Irritatingly I've flogged a precious a couple of days ago. The buyer has just sent me a message saying it arrived, works well, and has correctly detected a fault. I like happy customers

[1] not associated with a UK bank holiday.

[bd139]

Heads up that I've just noticed an unexpected[1] message in my fleabay inbox with a £1 selling offer. 

Irritatingly I've flogged a precious a couple of days ago. The buyer has just sent me a message saying it arrived, works well, and has correctly detected a fault. I like happy customers

[1] not associated with a UK bank holiday.

Excellent. Got that offer too. Next round of crap shifting commences.

[tggzzz]

Heads up that I've just noticed an unexpected[1] message in my fleabay inbox with a £1 selling offer. 

Irritatingly I've flogged a precious a couple of days ago. The buyer has just sent me a message saying it arrived, works well, and has correctly detected a fault. I like happy customers

[1] not associated with a UK bank holiday.

Excellent. Got that offer too. Next round of crap shifting commences.

The precious I shifted wasn't crap; it was electrically the best example I've seen. A little renovation lead to a nice profit, marred only by standard fleabay gouging.

I'd have kept it for myself, except that it is calibrated in units of 0.1ft(!) whereas the one I've kept is in metres.

[bd139]

Was that the one you were trying to sell me at Harwell? 

Mostly a monitor, stack of cisco routers and some clothes to sell now. Boring

[tggzzz]

Was that the one you were trying to sell me at Harwell? 

Quite possibly, but not sure; I've sold several. You would have got a bargain, tee hee.

It is rare to find a visibly working one. The front page of the military service manual gives clues as to why many of the fleabay examples are in suboptimal condition...

[Specmaster]

Heads up that I've just noticed an unexpected[1] message in my fleabay inbox with a £1 selling offer. 

Irritatingly I've flogged a precious a couple of days ago. The buyer has just sent me a message saying it arrived, works well, and has correctly detected a fault. I like happy customers

[1] not associated with a UK bank holiday.

Excellent. Got that offer too. Next round of crap shifting commences.

Same here, time to sort out stuff.

[tautech]

Someone please jump on this bargain:
https://www.ebay.com/itm/Tektronix-P6021-15-a-60-MHz-AC-Current-Probe-Stromzange-mit-Termination/164363906149?hash=item2644da2c65:g:U1wAAOSw2WBfTohi

[McBryce]

Someone please jump on this bargain:
https://www.ebay.com/itm/Tektronix-P6021-15-a-60-MHz-AC-Current-Probe-Stromzange-mit-Termination/164363906149?hash=item2644da2c65:g:U1wAAOSw2WBfTohi

Watching, but there's 18 bids in already, so I doubt it will be a bargain in 7 hours.

McBryce.

[Zucca]

Watching, but there's 18 bids in already, so I doubt it will be a bargain in 7 hours.
McBryce.

18 would be okay, the real problem is now the TEA platoon knows about it.

[Ero-Shan]

So I started the repairs of the newly arrived PSUs with the apparently simplest of them (and easiest to repair), the Conrad PS-302A.



A quick test showed that it was mostly working. However, the meter behaved erratically after mid scale. Also, the output did not reach 30 volts but maxed out around 28.

From behind, it was clear that the device had had some kind of incident involving mechanical stress ...



Maybe that incident was also causing damage to the meter?

Without the hood, a slight bending of the chassis could be seen, but there seemed to be no more damage. It could also be seen that this PSU couldn't qualify as a "laboratory" supply. I'd classify it as "hobbyist".



Removed the meter, found it to need 1 mA full-scale and having a resistance of about 300 Ω.
40 years ago I built my own power supply (from the magazine "ELO"). I had bought meters also, but never used them. One of them had a 30 V scale and 30 kΩ resistance. Bingo! So I took it apart to get rid of the series drop resistor. This turned out to be a 30 kΩ/5 % affair. The meter claimed to be class 2, though. The remaining resistance was 100 Ω - that might cause some problems.

Here's the meter's box, still with price tag. Per chance it comes from the same company as the PSU.



Both meters had the same size. While the original had a flat front face, the replacement (definitely the older one here) had a slightly konvex one. Alas, the frame was just a tad different, so the flat window would not snap onto it.
I decided to keep the original scale, which was glued on. Getting it off resulted in some bends and wiggles, which I straightened out as best as I could. Removing the nasty hardened glue required sanding. Then I had to cut off a few millimeters from the bottom and drill 2 holes before it could be fastened to the "new" meter.



The replacement does not fit exactly, but it was good enough for this device. Voltage readings were fine, but current was, as expected, way off. Twiddling with some of the trimmers, I was able to adjust the readings and also the max output voltage to the spec'd 30 volts.



Gave it to a friend, who'll put in in his attic ... likely to never be used again.