[AMPS] Info: Henry 2K HF AMP]

[Robert Neece]

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

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm