Test Equipment Anonymous (TEA) group therapy thread

[BU508A]

Forgotten what I ordered them for now though 

Edit: Current project is this tube of IRFZ24N's and a big heatsink I found cleaning out the cupboard. Decided that while ham radio is boring, building big RF amplifiers is fun (mainly because it's quite dangerous) so going to see if I can get 100W out of 4 of those buggers and a switcher I had lying around without blowing them to shreds

Aha.
Quote: "(mainly because it's quite dangerous)"

But why are you then afraid of voltages above, what was it? 40V? 50V? 

High power RF is not till then¹ fun when it comes with high voltages.   

¹got this phrase from LEO (online dictionary)

[bd139]

That's fair. For my perspective 100W into 50 ohms is fairly easy to keep contained at ~100v p-p and doesn't hang around once the DUT is turned off. Tubes, due to high impedances involved, tend to have to require ridiculously dangerous anode voltages to deliver some power whereas your typical MOSFET amps will quite happily run off 12-24V or so as they are crazy low impedance. Much easier to take precautions at those levels.  The main problems are explosions which mitigation is fairly easy with safety glasses and a sheet of perspex, both of which I own

Really though I've had an HT zap and an RF burn and I'd take the RF burn any day 

[med6753]

Was looking over the compensation procedure for the Type 1A2 plug-in and it's standard Tek stuff. HOWEVER....oh no  .....in order to gain access to the compensation controls the entire scope has to lay on it's side because the controls are on the bottom. 

It even specifies this in the manual. I thought I was done jack assing the 535A around. It's a total PITA and freaking heavy. 

This is gonna wait a while before I get to it.     

[beanflying]

Gosh our very own Spammer what a Rare event in here 

[BU508A]

That's fair. For my perspective 100W into 50 ohms is fairly easy to keep contained at ~100v p-p and doesn't hang around once the DUT is turned off. Tubes, due to high impedances involved, tend to have to require ridiculously dangerous anode voltages to deliver some power whereas your typical MOSFET amps will quite happily run off 12-24V or so as they are crazy low impedance. Much easier to take precautions at those levels.  The main problems are explosions which mitigation is fairly easy with safety glasses and a sheet of perspex, both of which I own

Really though I've had an HT zap and an RF burn and I'd take the RF burn any day 

Well, that's true regarding the low impedance of power MOSFETs. The huge disadvantage is the high currents for high power. If you are going up with the frequencies you need thicker wires because of the skin-effect. with higher voltages you don't have this problem. Next thing is the connections. You have to be very sure, that all of them are low impedance. It's a pita, if you have connection joints outside and they are going to oxidise. If I would build a high-power RF amplifier I'd follow the high voltage path. Carefully follow this path, of course. 

[BU508A]

Was looking over the compensation procedure for the Type 1A2 plug-in and it's standard Tek stuff. HOWEVER....oh no  .....in order to gain access to the compensation controls the entire scope has to lay on it's side because the controls are on the bottom. 

It even specifies this in the manual. I thought I was done jack assing the 535A around. It's a total PITA and freaking heavy. 

This is gonna wait a while before I get to it. 

How about a hole in your bench an a thing like that for cars?



And, of course, a mirror at the right place so you can see the waveforms. 

[Specmaster]

[...]

Reported to mods.

I already had, something has gone wrong because I understood that this style of spamming was prevented?

[BU508A]

perhaps Dave or Simon can explain this. 

[Cerebus]

Pah, all this talk of foolish grass cutting technology.

Cerebus says if you want grass cut get one of these

with one of these

or if there are daisies in the grass one of these


Or you could get Lord Julius or one of your politicians to talk the grass to death.

[Cerebus]

Was looking over the compensation procedure for the Type 1A2 plug-in and it's standard Tek stuff. HOWEVER....oh no  .....in order to gain access to the compensation controls the entire scope has to lay on it's side because the controls are on the bottom. 

It even specifies this in the manual. I thought I was done jack assing the 535A around. It's a total PITA and freaking heavy. 

This is gonna wait a while before I get to it. 

Perhaps you can get Cerebus' Nonna to do it for you?

[Brumby]

Gosh our very own Spammer what a Rare event in here 

... and I missed it.

You can get lucky every now and then.   

[xrunner]

Pah, all this talk of foolish grass cutting technology.

Cerebus says if you want grass cut get one of these ...

or - 

[bd139]

Or semi on topic... 



(Bob Widlar)

[WastelandTek]

Gosh our very own Spammer what a Rare event in here 

oh man, I missed it, nice cleanup guys

[Cerebus]

Pah, all this talk of foolish grass cutting technology.

Cerebus says if you want grass cut get one of these ...

or - 

(Attachment Link)

That is not a grass cutter, that is Lunch!

[Cerebus]

Or semi on topic... 



(Bob Widlar)

That is also lunch and the man Cerebus needs to help him with figuring out the high frequency current flow that is puzzling him in the current switched pulse-stretcher he is trying to design.

[bd139]

How are your skills as a necromancer?

[med6753]

Project for later today after I take care of some chores.

Capacitor replacement on an HP 6215A Power Supply. A little 500mA pipsqueak. 

It's my only HP. 

[BU508A]

Gosh our very own Spammer what a Rare event in here 

oh man, I missed it, nice cleanup guys

Not a good idea (from the spammer)  to mess with a bunch of engineers.   

[BU508A]

Project for later today after I take care of some chores.

Capacitor replacement on an HP 6215A Power Supply. A little 500mA pipsqueak. 

It's my only HP. 

What a cute little thing.

[mnementh]

good to hear.   I assume somebody brought the availability of the Tek 24x5 Siemens fan motors to the threads attention?   https://www.ebay.com/itm/274013390896

med needs two. 

[mnementh]

how's it going in here guys?

anybody get the plague yet??

Worse:              

mnem
I hate dat bitch. 

[Cerebus]

How are your skills as a necromancer?

Sadly lacking or else Cerebus wouldn't be going "Cerebus can see that 1ns peak is coming from junction capacitance there" (applies bypassing) "better, but why is the top of that square wave bowed, and why is it sloping down at the end if the input pulse is 100ns long, but not if it is shorter?" - Cerebus takes broadsword to LTSpice.

Seriously, I drafted, simulated and got this working (in spice) in an hour. Getting the linearity from ~1% to 0.1% was also easy, getting the 0.1% any lower is completely flummoxing me. I want to understand the causes and remedies before I start down the path of picking exotic hard to find low capacitance trannies. To be fair, I am trying to linearly stretch 50-100ns pulses to 1000 times longer or so (so they hang around long enough to count with a relatively slow clock), but in principle it is simple, but the devil is very much in the details.

[mnementh]

As I said before... the design criteria for most Briggs-powered mowers nowadays is to be a 10-year BIC lighter tool; use it up & throw it away. But if not abused, most will make it that long with nothing more than keeping a clean air filter on it and not running it dry of oil.

mnem
 

Yep, in another life I fixed B&S too and they're pretty simple to get longevity from. Despite their design faults just keeping the filter and oil clean was the secret of their success.

It's quite amazing how a chrome piston running a high silica alloy block can last as long as they do.

Yup. Just because it didn't work out for the Vega L4 (if they'd used EFI as originally intended, it probably would've had much better longevity) doesn't mean it's not good design for a mower. 

The newer generations have gone back to that KISS principle; making them fixed-speed with an aggressive governor curve prevents most dumbasses from over-revving them and starving the top-end for oil; the vane-operated choke mechanism prevents them from leaving the choke on or half-on and causing it to run rich and wash the rings dry with unburnt fuel. The plastic carburetor eliminated the aluminum scale buildup problems that have plagued all small engines since the dawn of time, and the addition of a functional recirculating PCV valve greatly reduces crankcase cavitation that once damaged oil rings. On top of that, these designs actually have fewer moving parts, and no metal/metal contact except what's inside the engine and lubricated with oil, so stuff seizing up and not working in the off-season is almost eliminated.

mnem
 

[Cerebus]

Yeah, but a Nonna will run for upwards of 90 years with just a little olive oil lubrication every day, and perhaps occasional lubrication with a drop of Grappa.