Adding a PIgnose G40V standby switch

[Enzo]

Except in direct heated cathodes like some rectifier tubes and really old power tubes like a 2A3, the heaters do not emit the electrons. The cathodes emit the electrons. All the heater does is make the cathode hot. That is its entire job. There is no heater emission, there is only cathode emission.

Oh someone will offer that some electrons do boil off the heater, but that is not part of the tube characteristic and is in fact not desirable. That is why we elevate the heaters by some DC amout, to PREVENT any electron emission from the heater itself.

The surface of the CATHODES erode away and they weaken their emission over time. But the heaters are not in that program. As long as the heater gets hot enough to make the cathode the 1500 degrees or whatever it is - I forget the exact number - then the heater is working. Heaters don't typically get a lot colder over their life. If I see a weak tube, I am going to assume the cathode is shot, not that the heater is cold.

[Robert M. Martinelli]

As long as the heater gets hot enough to make the cathode the 1500 degrees or whatever it is - I forget the exact number - then the heater is working. Heaters don't typically get a lot colder over their life. If I see a weak tube, I am going to assume the cathode is shot, not that the heater is cold.

Thanks Enzo,
I actually knew the difference between the "older" and "newer" tubes ( direct vs. indirect ) and I also knew that the emission comes from the cathode, but I was wrong assuming a sort of aging existed for heaters too - I was wrong, and your statement " Heaters don't typically get a lot colder over their life" made it perfectly clear to me.
Thanks!
Best regards
Bob

[Rob Mercure]

Bob,

The one thing that does happen to higher powered tubes - and some computer tubes - is that the cathodes develop a surface layer of electrons that then prevents further emission of electrons when the tubes are left heated with plate voltage and no signal. It is referred to as "sleeping sickness" and you can probably do a google and get a much better definition than my "QAD" (quick and dirty) one. While this was known for many years it really became a problem during the 1940s and 50s when tube computers were in use - in a binary system the "0" is a tube biased to cutoff with plate voltage applied and when you try to toggle it to a "1" by swinging the grid positive enough to conduct the tube would often offer no emission. This is why there are so very many industrial variants of the 12A_7 dual triodes - most were made for computer use while the rest were mostly designed for mobile radios with fluctuating heater voltages. The 5814 variant of the 12AU7, for example, was designed to resist sleeping sickness.
So this was/is one of the primary arguements for a standby switch. But, unfortunately, tubes sometimes just lose emission while in storage with no power of any kind. I recently sold a 1967 B-15N Ampeg Portaflex which drove me crazy as I prepared for sale. It had been sitting for a couple of years with perfectly good '80s manufacture Sylvania STR-387 6L6GC output tubes. But when I fired it up they were a dead as the dark of night - absolutely no emission. Since the amp worked perfectly when parked I spent several days pulling my hair out trying to figure out why the amp wasn't working until I decided to stick in a pair of funky Sovwrek 6L6's that I use a testing tubes and the amp worked beautifully! Weird! But I've still got 'em and someday I might overheat the cathodes (old radio trick) to see if I can get 'em emitting again but as best I can tell they caught sleeping sickness under cold conditions so the standby switch in the B-15N didn't prevent it.

Rob

[Robert M. Martinelli]

Bob,

The one thing that does happen to higher powered tubes - and some computer tubes - is that the cathodes develop a surface layer of electrons that then prevents further emission of electrons when the tubes are left heated with plate voltage and no signal. It is referred to as "sleeping sickness"
Rob

Thanks Rob, another ounce of knowledge to treasure - Oh, and I thought "sleeping sickness" was the thing I experiment every day when I wake up!

[Steve A.]

Hi Rob,
cathode stripping during idle is not an issue indeed...

Cathode strippers... spinning around the Anode pole on a hot Wednesday afternoon, sipping a cool beer while hiding out from the boss.

"Don't touch the merchandise," growls the muscular bouncer "or you'll be picking yourself up from the dumpster out back!"

... since we can't get rid of the SPAM around here, why not have some good old-fashioned amp porn?

http://www.blueguitar.org/new/misc/humor/amp_porn.pdf

Steve Ahola

[Robert M. Martinelli]

Cathode strippers... spinning around the Anode pole on a hot Wednesday afternoon, sipping a cool beer while hiding out from the boss.

"Don't touch the merchandise," growls the muscular bouncer "or you'll be picking yourself up from the dumpster out back!"

... since we can't get rid of the SPAM around here, why not have some good old-fashioned amp porn?

http://www.blueguitar.org/new/misc/humor/amp_porn.pdf

Steve Ahola

Steve,
after reading your truly hilarious post I REALLY wanted to take a look, but the link you provided is not working....is blueguitar down or something?Are they killing all the "good" sites one by one?

[Enzo]

The link works for me.

Try just going to the Blue Guitar home page, click on the site map on the left, and xscroll down a little bit to Misc/humor.

[scottme]

The link works for me.

Try just going to the Blue Guitar home page, click on the site map on the left, and xscroll down a little bit to Misc/humor.

Someone had a lot of spare time on their hands

I ended up using an input transformer that was twice what I needed, i.e. the Weber W022798 with half wave rectification. I'd like to revisit when I have some more time and get rid of the PCBs and put in a turret board and fix the power supply.

Thanks for all the great suggestions.