Robert Neece wrote:
A nice summation on the 2-K series:
>
> 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.
There was, additionally, a 2-KR offered...which was just the RF section
only, for
those who wanted to build their own power supply.
>
> 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).
This was, indeed, "fixed" by the time my 2K-3 was built ('68-'71...the
first
one to have the "new" 3-500Z's).
>
> 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.
I would guess that the intermediate 2K-2 ('67-'68) might accomodate the
taller
tube profile, as it was the "larger" cabinet, with "improved shielding"
and it
added an SWR bridge and separate band-switch positions for 80 and 75
meters and
silicon rectifiers in the PS to replace the 3B28 xenon rectifiers in the
original.
>
> 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.
Mine is non-stock power supply, so can't speak to this.
>
> 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.
The 2K-4 ('71-'75) was the first change to the "new" styling...tilted RF
deck, brushed
Al panel, square meters, recessed PS pedestal. The earilier series was
rounded cabinet
edges, two-tone grey, styled to complement the Collins S-line.
>
> 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.
Front-panel tune and load controls are gear-drive connected to the
respective caps.
Separate "scale" for each of the controls is calibrated from 0-200 in
increments of 2.
>
> 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.
Input is rated for 80 to 160 watts PEP. The adjustable pi-inputs can be
re-tuned
(within their respective limits) for any frequency from 3.5 to 29.7 Mc.
There were
a lot of these that saw MARS usage and Henry built a series of "export"
models as well.
>
> 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.
Manual for the 2K-3 states that it "will, of course, operate CW at its
full two
kilowatt rating" and gives instructions for retarding the load control
to operate
"at the FCC allowable one kilowatt input...power output in this
condition will be in
the 600 watt range." I'd guess that 1200++ out would be <very>
conservative.
>
> 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.
>
Yes, the "original" 2-K, reviewed in June '65 QST, had the "somewhat
unusual feature"
of the Pi-L tank circuit, which was discussed in more detail in the
foot-noted July
'62 QST article, but summarized by noting that it "has the advantage of
providing an
additional 10-to 15-db. attenuation of the second harmonic and even more
on the higher-
order harmonics"
> 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
Nice job from memory, Bob! I've only had mine a couple months and am
looking forward
to getting it back on the air.
73, Gerald W5BA
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