Which material has the highest breakdown-voltage?

[Joerg]

Hello John,

The big ole Tek tube scopes had a bimetallic timer tube (Amperite? 30
seconds?) that allowed the filaments to warm up before applying the
high voltages. This prevents cathode stripping and also keeps the HV
from being unloaded and going bezerk (the 5U4 rectifier filaments
heated up a lot faster than the other tubes.)

I also had a time delay to allow filaments and other stuff to come up.
This was usually the only transistorized part in the whole amp. But, I
have to admit that I had often grossly exceeded the plate current abs
max limit. This was in the college days when the $20 for a couple more
tubes were an insurmountable hurdle. Or let's say a priority hurdle
because $20 also bought you two crates of Grolsch ))

 

[John Larkin]

Hello John,


I also had a time delay to allow filaments and other stuff to come up.
This was usually the only transistorized part in the whole amp. But, I
have to admit that I had often grossly exceeded the plate current abs
max limit. This was in the college days when the $20 for a couple more
tubes were an insurmountable hurdle. Or let's say a priority hurdle
because $20 also bought you two crates of Grolsch ))

Yeah, I used to pay $7 for a CK722 whan you could get a steak and a
baked potato at the Buck Forty Nine restautant for, as I recall,
$1.49. And a Chinese lunch with coffee or tea and ice cream for
dessert was 85 cents. Hell, 1/4 watt carbon resistors cost 12 cents
each, and my allowance was $2 a week. Thank goodness for scrap TV
sets.

During my college days, at Houlihan's on Bourbon street, oysters were
10 cents each, and draft beer was a quarter, and the cheapest tunnel
diode was about $3.50 (no, not at Houlihan's!) Now a single oyster can
buy a hundred opamps.

John

 

[Tim Williams]

I thought it was a myth until I stripped down a tube that had decided to
disintegrate its glass cylinder. The cathode looked rather awful.

Yeah. AFAIK a non-issue under normal circumstances, but some less absormal
circuits and tubes can actually have appreciable wear.

Tim

 

[Joerg]

Hello John,

Yeah, I used to pay $7 for a CK722 whan you could get a steak and a
baked potato at the Buck Forty Nine restautant for, as I recall,
$1.49. And a Chinese lunch with coffee or tea and ice cream for
dessert was 85 cents. Hell, 1/4 watt carbon resistors cost 12 cents
each, and my allowance was $2 a week. Thank goodness for scrap TV
sets.

Oh yeah, I carted lots of TV sets home on my bicycle. In Europe we could
not buy the CK722. We had the old AC127 and for RF stuff the expensive
AF116. So I used triodes from TV tuners which were much better and free.

During my college days, at Houlihan's on Bourbon street, oysters were
10 cents each, and draft beer was a quarter, and the cheapest tunnel
diode was about $3.50 (no, not at Houlihan's!) Now a single oyster can
buy a hundred opamps.

And it's probably not even as good as they used to be (the oyster). As a
kid none of the shops ever had tunnel diodes. To us they remained
boutique parts, mentioned in many electronics recipes but unobtanium for
anyone without a fat defense budget.

Today kids could get some miracle parts for a song but most aren't
interested. Beer for the grown-ups is another matter. A growler of fresh
brew is now up to $10 out here. Ouch. Maybe time to start brewing our
own again.

 

[Tom Del Rosso]

I suspect that thin films sustain higher fields than bulk material,
and that a lot of these measurements are crap.

I was going to ask about this before I read the above.

air...20 kV/inch
20 V/mil
0.8 V/um
0.08 V for 0.1 micron die features

So I guess you're right about thin films.

 

[Joerg]

Hello Tom,

I was going to ask about this before I read the above.

air...20 kV/inch

That depends on which air. In many large US cities it seems people trust
air only when they can see it ;-)