[BC] Te st Your Wits on This

[RichardBJohnson at comcast.net]

Some tubes now have a gap in the sheet metal cylinder that encloses the anode fins. If that gap lines up with another gap in the plate-blocker, it could introduce some unanticipated inductance. However, this should not affect the neutralization, only plate tuning. Circuits that use screen-grid neutralization demand that the connection to the screen-grid ring be continuous. If the contacts are broken or dirty, all bets are off but you "might" find a position where there is enough contact area to neutralize.

Screen-grid neutralization, where shorting fingers are slid around a screen-grid connected slotted-ring were first introduced by RCA in their 10 kW amplifier. They were a maintenance headache. High gain tetrode amplifiers designed for non broadcast service use highly-reliable bridge neutralization. I made one of these for McMartin which produced 70 kW from a single RCA vacuum tube. They sold the first, but never went into production. The designs I made for the MRI industry were linear, had 30 dB of gain, and generated 35 kW. Neutralization was important because of the high gain. They used ordinary Eimac tubes.   

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Dana Puopolo" <dpuopolo at usa.net>

I have always made sure that I put new tubes back in the way old tubes came
out and found that neutralization was still good in most cases.