Stan, KB8JLV, writes:
>Can someone give me some info on this amp. Duty cycle, powr out with 100
>watts drive. How does it compare to my TL-922A. Are the 3-400 tubes
>similar or interchangeable with 3-500s?
The Henry 2K has been around in one version or another for
approximately 30 years. Henry produced so many variations on the
design over the years that it is difficult from memory alone to
be confident about particular characteristics. Further, I myself
have not owned a 2K. In spite of all of this, I'll take a stab
at answering your questions:
1. The original 2K was built in a floor-standing cabinet. That
makes it much less portable than a 922. Henry produced a
2KD soon afterwards that had a desk-top RF deck with a
separate power supply. In some of the 2KD iterations, the
power supply was not as rugged as in the floor-standing
versions. Moreover, some desk versions ran lower B+ voltage which
resulted in higher drive requirements and lower efficiency.
Henry used a tuned-choke-input B+ supply that was
"stiffer" (i.e., had better dynamic regulation) than the
capacitor input design in the 922 and most other desk-top units.
2. The original 2K suffered from a few weaknesses that were
corrected in later issues. As I recall, the very first
2K's had a pi-dux style coil in the tank circuit. This
was an airwound item with the windings spaced by
polystyrene or some such plastic. The pi-dux functioned
on 80 and 40 meters and, perhaps, 20 as well. Many ops
ran the 2K's hard, hard enough to melt the coil. Later
2K versions had edge-wound coils that were much more
tolerant of abuse (i.e., heat).
3. The RF compartment of the original 2K had a very low
profile. The interior height was just enough to
accommodate the height of the 3-400Z with plate cap.
The taller 3-500Z will not fit into this amp without
cabinet modification that is probably not particularly
cost effective.
4. The original 2K had a mercury-wetted power contactor on
the primary of the B+ transformer. These contactors were
reputed to have reliability problems.
5. Later 2K's, particularly the 2K-4, were much more rugged
(if not especially elegant) units that could take
quite a bit of punishment without complaint.
6. The Henrys have a reasonably resettable set of tune and load
controls having a numerical scale. This facilitates no-tune-
up band changes. This can be done on a 922 only by adding
a scale that one must calibrate himself.
7. The 2K series had user-adjustable input pi-networks for
each band. This made for efficient power transfer from
the exciter to the 3-400Z cathodes. This is a stretch on
my part, but I would suppose that the 2K would require
drive power that is similar to the 922.
8. The 2K was designed in the days when the ham power limit
was 1 kW input. The power supply was capable of more,
however, and *some* ops chose to "push" the amp to
somewhat reckless plate currents. I doubt that the 922
power supply, though designed for the 1.5 kW peak out
limit, has anything over the Henry.
9. Most Henrys feature a Pi-L tank circuit rather than the
simpler, straight Pi found in the 922. There are important
advantages to the Pi-L that are too elaborate to discuss
in this note. I am not certain, though, whether Henry had
settled on the Pi-L at the time the 2K was introduced.
Stan, I am sure that the amplifier "historians" among us can augment
or correct my rambling recollections on the unit about which you ask.
73 de Bob, K0KR
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