[Collins] 4D32 question

[Dr. Gerald N. Johnson]

On Mon, 2007-08-06 at 10:21 -0400, jeremy-ca wrote:
> They are not all of the same age. Raytheon built that tube from the 40's 
> until at least 1980. The USAF batch appears to have a 10 year spread. There 
> is also a FAA batch that was released but I don't know the date codes.
> 
> My concern was if seal leakage was a problem as it is with other tubes using 
> similar construction; 826, 829B, etc. Apparently it is not.
> 
> Carl
> KM1H
> 
Must be more uses I don't know about. I figured the tube for an orphan
when the 32V and Viking I went out of fashion.

I have no reason to believe that seal leakage in the 4D32 is no less of
a problem than it is with the tubes of similar construction. That's why
I recommended a couple days with heater power alone to let the getter be
warmed to do its work better followed by a gas check. The kind of gas
check where one puts +45 volts on the control grid, warms the cathode
until the grid current is about all the grid is rated for, Then puts -45
volts on the rest of the grids and the plate and looks for plate
current. That +45 on the grid accelerates a good emission limited stream
of electrons and should an electron in that stream encounter a molecule
of air, it gets ionized and its positive charge gets it drawn to the
plate where it reads as a current. Ideally one wishes that plate current
to be less than 1 millionth the grid current showing to a first
approximation that the vacuum is 1 millionth an atmosphere or better.
The geometry of a transmitting tube isn't optimized for such an
ionization gauge operation and probably indicates with some error,
though I think it was Eimac's VT-127 that was adopted for that and for
decades after WW2, Eimac showed a version with a glass tube for
connection to vacuum systems as a standard product.

Anyway, cook 'em, then check 'em for gas and if the gas gets good, use
them. More recent tubes have a chance of being better than old tubes,
I'd think.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer