Sound Quality Vs. Measurements

[ThorstenL]

Scott,

Originally Posted by scott wurcer

I concluded long ago that the engineer's finger is the electrostatic equivalent to ferrite beads.

Just be careful in tube circuits.

I prefer using an isolated screwdriver as the probe and several fingers curled around the isolated shaft to give the capacitance. The dielectric is usually only good to 500V or so, so be careful on Ham Transmitters running at 3KV anode voltage...

I once managed to touch the anode on a EL34 based guitar amp at a very uncool 700V DC by accident. It took a lot to repair the damage to the amp out of my pocket, lucky I got thrown free and did not get any current through vital organs.

I still occasional show the burn mark scars to young and eager DIY'ers who want to play with high voltages and tell them - that was death right here, avoided by an inch because the hand also touched the chassis and completed the loop rather than something that was important (that was probably when I lost one of my nine lives).

They usually then get fascinated with the very obvious scars I got on the same hand (left - I'm right-handed so I use left for dangerous missions) from taking someone's knife away by the blade (don't ask, but that was another of my nine lifes), which kinda of spoils the lesson...

Ciao T

[bcarso]

Originally Posted by scott wurcer

I concluded long ago that the engineer's finger is the electrostatic equivalent to ferrite beads.

Of course we would always joke that the tech/engineer had to be shipped with the product, or at least the engineering sample.

I loved power supplies in my early knowing-next-to-nothing days. One requirement was for a constant current supply for hollow-cathode discharge lamps for spectroscopic calibration. So I decided if some regulation was good, more was better. Being a bit hazy on loop stability analysis I was accustomed to determining compensation by the cut-and-try method.

But in addition to having far too many stages to make compensation straightforward, I also had the system running directly off the unisolated mains with a cap-diode voltage tripler Three hefty 450V computer-grade electrolytics. And worse still, the control electronics floated at the high voltage, around 500V.

So I'm probing the circuitboard with little capacitors. At least I had learned the one hand in the pocket rule, so most of the damage was when things were jerked off the bench and thrown to the floor.

It did eventually work, although required substantial series resistance with the tubes to make the load line a bit more tractable.

[a.wayne]

That's why I'm limited to 50v psu's .........

[ThorstenL]

Originally Posted by bcarso

So I'm probing the circuitboard with little capacitors. At least I had learned the one hand in the pocket rule, so most of the damage was when things were jerked off the bench and thrown to the floor.

Isolated 'lectricians screwdriver mate, take me word.

Capacitor leads can be wrapped to the blade.

Did I ever tell the story of the one time I got shocked and was lucky not to be thrown free?

It was above a sludge channel in a steel work, not only was the sludge very acidic but it was quite poisonous, not recommended to take an adult swim there by a long stretch.

I got stuck with my hand on a relay when I grabbed the back of the wiring in an open, live wiring closet (all against health and safety regs of course, it should have been shut down to work on - at around 500K USD loss per hour downtime - fat chance) and my hand and arm like cramped for almost 5 minutes. Until the relay mercifully closed with a massive clunk and I had the presence of mind to grab the frame (not the wiring) with my other hand. My arm hurt bad for days.

That was the worst I think. I escaped being turned into the statue of the heroic worker ('tis woz commie thymes) by having liquid steel poured on me and me mates by a few seconds, otherwise that would have been the worst, but I'd not be around to brag 'bout it, which would sux.

Ciao T

[john curl]

Thorsten, you remind me of the 'good old days'. Back in 1959, working on my 1938 Gibson Guitar Amp ( electrodynamic coil speaker), I got across the B+ in a damp garage and it virtually knocked me across the room. (And people wonder why I prefer solid state ;-)

[a.wayne]

I guess this is how your steady diet of feed forward started ......

[Wavebourn]

Troubleshooting of tube gear in the field can be dangerous as well.
I once grabbed chassis by both hands and pulled the amp that was standing on a stage to turn over and see under the chassis where the smoke is coming from. It was hot day during that rehersal so I was half-naked, and one cap in a voltage doubler (about 300V on it's case) touched my naked belly. Ouch!
Speaking of oscillations and capacitances, I routinely used to add 1-10K resistor to the tip of oscilloscope working on SS designs.

[dvv]

Ooooohh, you guys are so high tech ...

I was almost electrocuted by my dishwashing machine. It had a ribbon cable from the stand to the door, where the controls were located, so every time the door was opened, those cables were twisted front and back. Eventually, one of them gave up the ghost, and it was probably the power conductor, because when I touched the door, I rememebr being very surprised at what was I doing across the kitchen.

Compunded mistakes - my wife didn't turn it off (controls are all plastic) and I didn't unplug it from the wall socket, as I should have done.

But unlike you, I didn't have to go to exotic places to touch weird relays, nor did I need a test bench full of tube gear, a simple dishwasher was enough for me, I'm a humble kinda guy.

My advice to you is never buy an Italian Candy dishwasher machine, and thank your lucky stars, as I did, for having the good sense to cover the terazzo cement floor of the kitchen with a plastic covering.

[ThorstenL]

John,

Originally Posted by john curl

Thorsten, you remind me of the 'good old days'.

In many ways eastern europe was "behind" on tech. So despite being a few decades your junior (not as many as I wish though) I got more than fair exposure to that kind of stuff.

Also, in Eastern Europe we did not have the commercial pressure to replace everything with next new thing. Consumer production was very low. You had to get on a waiting list to buy a car. My parents put me down when I was 2 or so, being "next in line" for a car allowed me to make so much profit on the black market, I was able to buy an old Lada, rebuild it and still pay for most the first Band/DJ sound system, when I had just turned 18...

We just did not throw things away. In my first band in the early 80's we had (donated by state youth organisation) a real Fender-Rhodes Piano and a real Leslie Organ, needed a lot of work, but these two made a lot of our sound, especially the Fender-Rohdes had such a lovely tone on leading lines...

At the time my TV was a Russian Raduga Colour TV, hacked for receiving west german TV, the Raduga had tubes everywhere where things connected to the picture tube and you could really crank up the cathode currents and anode voltage on the picture tube (this gives a brighter and sharper picture for all those who only know newly fangled Sony Trinitrons and LCD screens), the unavoidable occasional flashovers would just cause a "white blink". The much more modern and high tech east german TV's (full of IC's and silicon) would react to the same kind of flashover on the picture tube with the need for a total rebuild and so had a crappy picture...

Originally Posted by john curl

(And people wonder why I prefer solid state ;-)

Well, friends of mine homebuild ESL Panels and drive them directly of tube anodes with around 1500V on the anodes. Now THAT is scary. REAL scary... 10KV supply to the panel and around 1000V RMS on each stator with around 160mA peak current available undistorted.

The stators are powder coated, but trust me, I do not step up close when the system is energised. We are talking Enterprise dilithium core grade stuff here - I prefer to not be sacrificed for the good of the many.

That sh..t is scary.

Ciao T

[ThorstenL]

Hi,

Originally Posted by dvv

I was almost electrocuted by my dishwashing machine.

Now in London (that would have been around '97), one time I was bothered by shocks I got from the cable TV box. I was living in a Nurses home at the time -working for the NHS - some of those nurses where quite cute and saucy - we eventually found out the house earth was somehow at around 180V RMS...

Good thing we had no dishwashers, washing machines etc. (washing was done central, the kitchen was gas and did not have single electrical appliance!)...

Ciao T