Gents:
Just tried to install two new Eimac 3-500Z tubes I bought from two different
guys. One of the tube was new in an unopened Eimac yellow box, with a 1995
date code. The other was new in an opened box, with a 1993 date code.
Previously, amplifier would not make more than 600W on 40, and went down to
300W on 10 meters.
160 and 80/75 had full output. Tubes had 1976 date code so I figured they were
soft. But amp worked... well, kinda. I won't mention the overheating and
buzzing power supply!
Now with the newer tubes in it, when I key the amp, the power situation is
different. The amp tunes up (plate dips, loading OK, has gain) but makes funny
noises, and still won't put out full power. Also perhaps notable, the meter
lamps dim appreciably when amp is keyed (this didn't happen with old tubes).
According to the schematic, the illumination lamps are across the filament
supply. I did replace the lamps, same type as originals, and non-keyed
brilliance is OK.
I ran the new tubes with filaments only -for 6 hours- before applying plate
voltage.
Questions:
1. Do I have a grid-filament short in one of the 'new' tubes?
2. Does anyone have a full-output, late-date-code Eimac bottle for sale?
3. Anyone care to comment why the amp might still tune up, have correct idling
plate current, and put power out - if there is such a nasty problem with a
tube?
thanks....
* * *
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Bay Architecture Lab
Research Triangle Park, NC
(919) 941-1726
sjackson@baynetworks.com
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</bigger>KZ1X/4
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"It is always morning somewhere in the world."
...inscription on the Great Sundial, Helen Keller Rose Garden
Morehead Planetarium, University of North Carolina at Chapel
Hill
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