[Amps] Recommended Method to Install Transmitting Tubes

Traian yo9fzs at office.deck.ro
Mon Jan 27 10:27:13 EST 2003

Hello Dave,

On the very first page of the Harris RF-110A amplifier
Instruction Manual (even before the contents table),
you may read the following:

The tubes used in the final amplifier stage of the RF-110A
Power Amplifier may occassionally liberate minute amounts
of gas during prolonged storage, according to the manufacturer.
To prevent degradation of performance, it is advisable to run
the tubes without high voltages applied following storage
periods, to remove any gas from the tubes.
Therefore, it is strongly recommended that upon installation of
this system, or following any period of three or more months
duration without operating the system, that the system be run
for at least 30 minutes in the STANDBY mode before going
to any operating mode."

The RF-110A use two RCA 8122 (as drivers) and two
Eimac 4CX1500B tubes.
Please note the "according to the manufacturer" (i.e. Eimac)
detail included in the Harris warning.
Note also that the for the STANDBY mode, the high
voltages of the RF-110A (anode and screen) are off.

I got two amps, finals having 1977 date code on them.
One amp had about 2000 hours on (on an aircraft) and the
other about 200 hours only (was a spare amp at the base).
I am sure that they had some years of unoperating time.
As the specified tubes are very, very hard to find here and
very costly (at least for me), I fololowed the warning and
got out the finals and let (actually forgot) them for about 10
hours with applied filament voltage only (2 series connected
tubes filaments, using an Astron SS-30 PS and also two
computer fans to avoid overheat  and/or burning of the
soft table cover...).
These tubes never arced and had no discharge during the
tests at up to (accidentally) twice the amps rated output
(the RF-110A amps are very conservatively rated also).

Hope to help,

Dave Smith wrote:

> Friends,
> What is the recommended method to pre-condition a
> "USED" pair of 3CX800A7's. These tubes have been out
> of service for a couple of years and I need to replace
> a pair of flat 3CX800A7's in my Lunar-Link, 2 mater,
> PA. Is is recommended to leave filament voltage on for
> several hours before applying HV? Is it recommended to
> leave HV turned on before applying drive power?
> I've looked through EIMAC's "Care and Feeding of Power
> Grid Tubes" but can not find any reference to
> pre-conditioning tubes for use.
> Thanks for your input.
> Dave / W6TE
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