Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

Use this form to submit comments directly to the Asylum moderators for this forum. We're particularly interested in truly outstanding posts that might be added to our FAQs.
You may also use this form to provide feedback or to call attention to messages that may be in violation of our content rules.

You must login to use this feature.

Inmate Login

By default, logging in will set a session cookie that disappears when you close your browser. Clicking on the 'Remember my Moniker & Password' below will cause a permanent 'Login Cookie' to be set.

Moniker/Username: The Name that you picked or by default, your email. Forgot Moniker?	Examples "Rapper", "Bob W", "joe@aol.com".
Password:	Forgot Password?
	Remember my Moniker & Password ( What's this?)

If you don't have an Asylum Account, you can create one by clicking Here.

Our privacy policy can be reviewed by clicking Here.

Inmate Comments

From:
Your Email:
Subject:

Message Comments

Original Message

Idea for Prolonging Tube Life

Posted by Lee of Omaha on September 1, 2011 at 08:37:05:
My understanding of the way tubes wear out is that the few billion molecules of gas left in tubes get positively ionized by the bombardment of electrons passing from cathode to plate. A few of these massive (relative to an electron, anyway) objects make it past the protective cloud of electrons protecting the cathode and strike the cathode. These impacts physically abrade off the oxides that emit electrons. After a while (determined by evacuation of the tube, quality of the electron cloud, voltage the plate and grid are operated at, and probably other factors) enough of the oxide has been removed so that the emission of the tube is meaningfully decreased. Residual gas is the bad guy.

I've never seen an analysis of the gases left in tubes. My hypothesis is that since as a good approximation hydrogen leaks through anything, that at least a disproportionate amount of the gas in tubes is hydrogen that has leaked in through seals and even straight through the metal parts such as the leads. Helium is right behind hydrogen in leakiness, so there cold be a little helium in there too.

So the idea, at least for signal tubes, is to surround the glass envelope with a second glass envelope leaving a small gap between the two. A nipple would be fitted to the outer envelope and the signal tubes in a device would be connected to a a common continuously running vacuum pump. This should keep down leakage into the tube of light gasses by limiting the amount of gas in contact with the inner envelope. The vacuum pump wouldn't have to be very good to have a significant effect on tube life, if my conjecture is correct. Quietness of the pump would be important, though.