Heathkit HA-14 Quick Start Manual

Introduction
The Heathkit HA-14 was one of the few electron tube linear amplifiers intended for
mobile use but few were purchased with the 12 volt mobile power supply. Most hams
bought the HA-14 for base station use; it was small, lightweight, and ran a healthy "one
kilowatt" input with its compact 110 volt A.C. power supply.
I first purchased one in 1993 to serve as a backup for my other amplifier. I found it to be
much easier to use than my "big" amp (AL-1200) which requires a long warm-up and
careful tuning. The HA-14 gave me a 6 DB boost with instant warm-up and one knob
tuning. Given my very favorable experience, I thought I'd purchase another HA-14 and
modify it for 6 meters; Ebay accommodated my wishes at a very reasonable price! Note:
The HA-14 does convert to 6 meters BUT if you are looking for an easy conversion, buy
an SB-200; it requires little physical modification for conversion.
Modification Strategy
The HA-14 is very similar to the Heathkit SB-200 amplifier; both share many identical
components including the tubes, a pair of 572-B's. There have been several articles on
how to modify the SB-200 for 6 meters. It was my hope that the HA-14 could be
modified using these articles. One of the differences is that the HA-14 has the filaments
of the tubes is series (for mobile 12 volt use) however, the most unique aspect of the HA-
14 design is that it only has a plate tuning control in the PI network; the plate loading is a
fixed 350 PF capacitor for all bands. I hoped to modify the 10 meter position and retain
the ability to operate 80 through 15 meters. Many weeks of unsuccessful efforts finally
convinced me that this was not practical and I would have to convert it to be a single
band amplifier. My failure to multi-band the HA-14 was mostly due to the physical
layout of components, particularly the plate tuning control which was a great distance
from the tubes. My aborted first attempt convinced me that it would be extremely
difficult to have a fixed capacitor for the plate loading portion of the PI network because
the tuning was extremely sensitive and that lead length in the tuned portions of the
amplifier were very critical for 6 meter operation.
Given these factors, the resulting modification strategy was:
1. Settle for single band operation
2. Add an additional variable capacitor for plate loading
3. Minimize lead lengths in tuned circuit components as much as possible
Modification – Additional Parts Required
The list of parts is as follows:
1. A 5 KV variable capacitor physically similar to the existing plate tuning
capacitor with a low MINIMUM capacitance (preferably 4 PF or less) and a
maximum of about 50 to 70 PF that can fit in the space occupied by the
existing band switch elements in the output area of the amplifier (See Figure
3.0). I used one I had in my junk box and I removed two sets of plates from
the capacitor with a long-nose pliers. Several capacitors compatible with this
Modifying The Heath HA-14 For 6 Meters
Greg Chartrand - W7MY
4/22/07
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