Test Equipment Anonymous (TEA) group therapy thread

[bd139]

Nah. We're busy drinking our TEA, not throwing it in the sea

I actually spent the entire morning in the hospital after my youngest decided to do discover Newton's second law with the aid of some monkey bars  . Fortunately just a green stick fracture, nothing serious. I did the same thing when I was a kid at least three times.

Bleah...you can have your tea. Coffee here. 

Ouch....glad she's OK.

Proof you don't run from the Po-po........current on the scanner and it's getting ugly: Kids stole car. Police spotted them, attempted to stop vehicle. Kids took off with police in pursuit. Car crashes with roll over and catches fire. Passenger out. Driver currently trapped. Fire/EMS currently in route. Medivac chopper being put on standby.

Update....both suspects now out. Driver head injuries. Chopper being launched.     

Yeah got to be honest I'm sitting here drinking coffee. I can't stand tea

Around here they just let them go rather than chase them. Makes sense in a densely populated area. 2/3 of the RTA deaths here involving the police were pedestrians or passengers. We do have very well organsised vigilante groups in London though who do trace and take down the crims.

[med6753]

Police chases in this rural area are rare, but every once in a while I catch what they call "failure to comply".

Whatever is going down at that current scene is getting interesting. The County District Attorney has responded. I'll bet he's real happy on his day off he has to work. 

[Neomys Sapiens]

We had a chase involving a couple in a sizeable motor home two days ago, which happened to have been unregistered and uninsured. when they discovered it first, they just left it to the owner because he claimed to be living in it under the condition that it stays where it is. Later, a patrol saw it rolling and started to pursuit. Quite a show, as he did not stop, they hurled things at the police and finally locked themselves in the vehicle in the mid of a road.

[Neomys Sapiens]

Yeah... that's the only reason they had "a few days" to niggle at me. I TRIED to talk myself out of them... I REALLY DID.   

But even the "You're moving, dumbass!" argument proved unconvincing... I just said to myself:

"For THOSE juiceboxes, I'll jettison one of the THREE air compressors I have to make room!!!"

"B-b-b-ut..." 

"AND A PLANE, IF I HAVE TO!!!"   

Myself tried to put up a brave front and talk me down to just one, but we both knew the battle was lost in that instant... 

mnem
If nothing else, I am a creature of strong convictions.

I had expected that you wold have them sent ahead! And the plane?,,,giving up on woodworking?

[worsthorse]

Yeah that's not good. My old "scariac" was wired with one autotransformer variac and then an isolation transformer.

The solo variacs are good for driving kit to test power supply regulation and that's about it. Never use them for debugging stuff!

Edit: scariac because it weighed 35Kg

Yup. I have an isolation transformer (the GRP-1200) and a variac (the Amsco Variable Intensity Control that @mnen gifted me to replace the one I foolishly sold). I keep 'em separate so I am less likely to do something that could kill me.  That said, he rule is still one hand in the pocket if I have more than 5VDC into a circuit I am probing, a lesson I learned by getting knocked on my young and not-too-bright ass a couple of times oh so long ago.

[Kosmic]

Stuck home with a cold today. Doesn't make too much sense it's like 30deg outside.

Anyhow, I spend some time playing with the Rubidium reference I got some time ago. Incredible how close it is from the HP 5335a (high stability option).

[Specmaster]

Police chases in this rural area are rare, but every once in a while I catch what they call "failure to comply".

Whatever is going down at that current scene is getting interesting. The County District Attorney has responded. I'll bet he's real happy on his day off he has to work. 

I used to enjoy listening in to the Police and other emergency services but then they went and spoiled the fun by switching to Tetra, bloody killjoys. 

[med6753]

Police chases in this rural area are rare, but every once in a while I catch what they call "failure to comply".

Whatever is going down at that current scene is getting interesting. The County District Attorney has responded. I'll bet he's real happy on his day off he has to work. 

I used to enjoy listening in to the Police and other emergency services but then they went and spoiled the fun by switching to Tetra, bloody killjoys. 

I'm lucky in that my county is a bunch of cheap skates. They have a first class 911 center but antique radio system. Most radio is still on VHF simplex. They haven't even gone to 800MHz trunk.  And the State Police are VHF duplex which is still listenable.

[mnementh]

   Took a cheap ebay variac and disconnected the mains socket, voltage dial, and added test lead jacks.  So I can prototype PSUs without having to have a gazillion different transformers on hand.  Waiting to receive a green jack for earth.  Will probably also remove the mains jack altogether and 3D print a couple of covers for the holes.

If your intent is to drive another transformer with that, fair enough. Just be mindful that it is an autotransformer, so the secondary is tied to the primary side, unlike a proper transformer that maintains isolation from mains voltage. Of course, for that, there was no need to remove those parts, so... *cringe* 

mnem
*toddles off to ded*

I was wondering the same thing. Bson, are you sure the primary and secondary are totally isolated from each other? Your intention is a great idea but only if you are truly isolated from the mains. Otherwise you could be in for a world of hurt. 

Yeah, I know for a fact that unit is NOT isolated. I've had a few of them apart. 

I have a 90VA & a 300VA 1:2 line transformer I use for this purpose with my AMSCO VARIAC. If I want low voltage AC for prototyping, I use it backwards and I can get stable output down to about 6VAC @ 1.5A; lower at less current. If I need line voltage, I turn it forward and crank the VARIAC down; I can still get full 300-350VA output with the VARIAC at 50%.  The problem with this approach is that you have to be EXTRA CAREFUL... a lot of these step-up/step-down transformers are ALSO autotransformers, and so defeat the purpose of using them for isolation in the first place.

med6753 - That's the way you could do it back when there were plenty of cheap transformers available. I used to wire identical back-to-back tube type power transformers with 500 vac hv windings to make isolation transformers. If the added voltage drop was a problem I'd wire the filament windings in series adding to compensate.

If you just needed voltage correction without isolation you could use a low voltage transformer with its secondary in series with the line to boost or buck the line voltage (see drawing). This allowed a relatively small transformer to correct a relatively large output current. The output current rating was equal to the low voltage secondary rating. Some of the line conditioners sold today use this scheme with sensing circuits and relays to automatically correct for line variations over a wide range.

For even more fun, I'll wire a dim bulb tester in series with the above contraption for quick & dirty current limiting. I keep 7W, 15W, 40W, 60W & 100W incandescent bulbs and one of those light blub "Y" adapters to come up with "best guess" current limiting. 

   And then there's THIS little suicide box... Essentially a dim-bulb tester with a bridge rectifier on the outputs. Good for quick SMPS proto work and desulfating lead-acid batteries. Provided you can put it behind a locked door to keep little fingers away. Hmmm... I can make some of the room I need for my LAMBDAs by adding a simple DPDT to the output of this as a bypass...  then I can get rid of my big dim-bulb tester... 

mnem
Don't get me thinking... that's a dangerous thing. 

[bson]

If your intent is to drive another transformer with that, fair enough. Just be mindful that it is an autotransformer, so the secondary is tied to the primary side, unlike a proper transformer that maintains isolation from mains voltage. Of course, for that, there was no need to remove those parts, so... *cringe* 

I guess I should have mentioned I always use an isolation transformer.  It's possible, perhaps, depending on the winding to cut the common neutral, but I didn't check.

[bson]

Edit: Oh, and the "voltage dial" you removed was the output voltmeter which would be a good idea to keep in the circuit.

It already has markings on the knob and the stupid needle toy meter is no more or less precise.  I use a proper meter to set the output.  If I don't trust something I won't use it, and if I won't use it it's just taking up space.  So I just get rid of it up front.  The switch is lit, and while that doesn't guarantee there's anything on the outputs I'll just assume there is.  This thing is actually pretty robust and reasonably well built, so once the plastic junk meter is removed there's really nothing left to fail, except the fuse...  (Which I dropped down to 750mA, I really don't need 5A for my uses.)

[bson]

I also don't envision needing more than 50V peak, so I may put in a bolt to keep the knob from turning past 36V or so.

[med6753]

Got a good lesson in proper termination. Was playing around with the 7904 and was curious about the “Sig Out” BNC on the front panel. I figured that would be a good place to connect a frequency counter. So connected up the Fluke 1900A. It works but there's a problem. The input is 10MHz. The Fluke is reading 20MHz. Huh?



So....connected that output to the 2465DMS with counter readout. Sure enough, 20MHz. And that trace is downright ugly. It should be a square wave.



Let's try something. Switch the 2465 to 50 ohm input impedance. Ah ha!. Square wave, 10MHz. As it should be. The Fluke has 1MEG input impedance. That explains it. I need to get some 50 ohm feed thru terminators. Hello Amazon.   

[0culus]

Funnily enough I hadn't even thought of doing that with my 7904A's sig out. I have two counters with 50 ohm inputs though, so I'm definitely giving this a try.

[med6753]

And I think I need to step up my game and get some better frequency counters. Hello HP and hello time nut. 

[bd139]

ONE OF US. ONE OF US!

[med6753]

ONE OF US. ONE OF US!

What would be a good choice? Should have at least 225MHz B/W and would prefer LED readout. Not liking the HP's with the LCD's.

[0culus]

And I think I need to step up my game and get some better frequency counters. Hello HP and hello time nut. 

I have a 5335A with all options, and a 5350B. The 5350B (in absence of a working GPSDO) runs off the oven ref out of the 5335A, which gives me a pretty darn good reference. In turn, I have my 53310A hooked up to the ref out of the 5350B which passes the reference signal.

...once I get moved (hopefully in a few weeks time) into my new place, a GPSDO + distribution amp is high on my list.

[med6753]

And I think I need to step up my game and get some better frequency counters. Hello HP and hello time nut. 

I have a 5335A with all options, and a 5350B. The 5350B (in absence of a working GPSDO) runs off the oven ref out of the 5335A, which gives me a pretty darn good reference. In turn, I have my 53310A hooked up to the ref out of the 5350B which passes the reference signal.

...once I get moved (hopefully in a few weeks time) into my new place, a GPSDO + distribution amp is high on my list.

Whoa! I ain't ready to dive in that deep...yet. 

[0culus]

The 5335A with the optional C input is very capable. Input C gets you up to 1.3 GHz or so. Mine even has the voltmeter option!

[med6753]

The 5335A with the optional C input is very capable. Input C gets you up to 1.3 GHz or so. Mine even has the voltmeter option!

Holy shit....I told you. I ain't ready to dive in THAT deep just yet.  Something smaller, less complicated.....and MUCH fucking cheaper. 

[mnementh]

Yeah... that's the only reason they had "a few days" to niggle at me. I TRIED to talk myself out of them... I REALLY DID.   

But even the "You're moving, dumbass!" argument proved unconvincing... I just said to myself:

"For THOSE juiceboxes, I'll jettison one of the THREE air compressors I have to make room!!!"

"B-b-b-ut..." 

"AND A PLANE, IF I HAVE TO!!!"   

Myself tried to put up a brave front and talk me down to just one, but we both knew the battle was lost in that instant... 

mnem
If nothing else, I am a creature of strong convictions.

I had expected that you wold have them sent ahead! And the plane...? giving up on woodworking?

   Plane... Not plane:   

If your intent is to drive another transformer with that, fair enough. Just be mindful that it is an autotransformer, so the secondary is tied to the primary side, unlike a proper transformer that maintains isolation from mains voltage. Of course, for that, there was no need to remove those parts, so... *cringe* 

I guess I should have mentioned I always use an isolation transformer.  It's possible, perhaps, depending on the winding to cut the common neutral, but I didn't check.

Yes, but if you're going to bridge-rectify (or even half-wave rectify) that output, you want the iso-former AFTER the VARIAC. Hence, no need to dismantle anything.  If you have a diode go short in your rectification, you have the potential for much-higher-than-expected voltages in the output.

For those playing along at home... Never EVER power any DC supply directly from a VARIAC.     Okay... now that we have the obligatory PSA out of the way, we can resume our normal insanity.   

If you open up the common neutral on a VARIAC, it stops working as it provides necessary excitation to the wiper. If you do that on an autotransformer, the voltage drops way down as does the current capacity. Just put the iso-former AFTER the VARIAC. 

ONE OF US. ONE OF US!

   

mnem
*currently taking care of a sick wife*

[0culus]

The 5335A with the optional C input is very capable. Input C gets you up to 1.3 GHz or so. Mine even has the voltmeter option!

Holy shit....I told you. I ain't ready to dive in THAT deep just yet.  Something smaller, less complicated.....and MUCH fucking cheaper. 

 

TEA corrupts absolutely....you'll fall yet.   

[mnementh]

*Huggles his 189 close* "There, there... I'll never need more than you; my one, my only, my precioussss..." 

mnem
 

[bd139]

ONE OF US. ONE OF US!

What would be a good choice? Should have at least 225MHz B/W and would prefer LED readout. Not liking the HP's with the LCD's.

5334B with channel C and OCXO. Silent, 50 ohm termination, does everything.

Cheap option: Looks like they frequently get sold as spares repair showing “no osc” but the external oscillator is switched in on the back 

Paid $80 equivalent for mine. Adding channel C myself for around $20 and external OCXO for $20 in parts.

I would stay away from the A version. It has a battery in it which leaks.