The Hammarlund HQ100A Receiver

The Hammarlund HQ100A Receiver
Vintage Radio
by Mark Spencer, WA8SME
The Hammarlund HQ100A Receiver
After more than five decades, it remains a classic!
Harold Kramer, WJ1B
ARRL Chief Operating Officer
My grandfather gave me a new Hammarlund HQ100A receiver just after I got my
Novice license in 1963. We purchased it at
the Harrison Electronics store at 225
Greenwich Street in New York City. Although he was not a ham, my grandfather
owned a radio and television sales and service business, so he was familiar with electronic equipment. I used this receiver for
many years on 80, 40, and 15 meter CW
and, with an Ameco 2 meter Nuvistor converter, on 2 meter AM and CW.
Hammarlund History
The Hammarlund Company was founded
in 1910 by Oscar Hammarlund, an innovative electrical engineer who was originally
from Sweden. The Elgin Watch Company
brought him to the United States for his
engineering expertise; however, after
working for both Elgin and Western Electric, he founded his own company. When
we purchased the HQ100A, Hammarlund
was one of the oldest and most respected
companies in the electronic manufacturing
business. In the 1950s, the company was
sold to Telechrome, who later sold it to the
Giannini Scientific Company. It was sold
again in the late 1960s to the Electronic
Assistance Corporation (EAC), who
owned it until the early 1970s when they
closed the company and sold off the remaining equipment to The Cardwell Condenser Corporation.
Originally the company specialized in producing electrical components. Oscar Hammarlund was the inventor of the split
variable condenser (capacitor) that was
used in almost all broadcast and communications receivers for decades. From its inception, the Hammarlund logo was a
variable capacitor.
The Hammarlund Company produced
thousands of communications receivers
for the government, commercial, Citizens
Band, and Amateur Radio markets. The
first Hammarlund communications receiver was the Comet Pro, which debuted
around 1931. The SP200 and SP400 models were introduced after that and the high
performance Super-Pro SP-600 debuted in
1947. The receiver line continued with the
amateur and shortwave band vacuum tube
receivers numbered HQ100 through 180
and the solid state model HQ 215. As the
model numbers increased, so did the price
and performance of the receivers. While
Hammarlund specialized in receivers, it
also manufactured a few models of amateur transmitters and linear amplifiers. The
best known are the HX-50, AM/CW/SSB,
100 W transmitter that debuted in 1967,
and the 1500 W HXL-1 linear amplifier
that was launched in 1964.
The Distinctive HQ100A
My HQ100AC (the “C” meant that it had
a clock) was introduced in 1962. It was the
least expensive communications receiver
in the Hammarlund line. The HQ100C
was the successor to the HQ100, which
was introduced in 1957. Both were general
coverage receivers that tuned from .54 to
30MHz. The major difference between the
two receivers was that the 100A had a true
BFO (Beat Frequency Oscillator) circuit
for receiving CW and SSB. The HQ100
simply drove its Q-multiplier into regeneration for its BFO.
Like all Hammarlund receivers, the
HQ100A is handsome and ruggedly built.
The under-chassis components are handwired and neatly arranged. It is slightly
wider than it is tall, and housed in an attractive cabinet. An extruded overhanging
ridge surrounds the front of the cabinet and
a bold “HAMMARLUND” is prominently displayed on the front. This look
was common to all latter-day Hammarlund
The gunmetal gray front panel has 13 controls that are symmetrically arranged and
logically grouped. The black, fluted controls have bright white labels. The smaller
controls are still nicely sized, with white
marker stripes on the knob and on the circular area surrounding the controls, making it easy to remember where they should
be set. The two toggle switches, for AVC or
MAN[ual], and for LIM[iter] ON or OFF,
have a pronounced snap when thrown.
The Telechron clock/timer displays
24-hour time. The timer is used, according
QST ® – Devoted entirely to Amateur Radio
June 2014 95
to the manual, to “turn on the receiver
ahead of anticipated operating time” so
that it would be stable and at “a predetermined operating temperature.” The radio
drifted when cold, so a warm-up period
helped frequency stability.
Under the hood, the HQ100AC is a single
conversion, four-band, superheterodyne
receiver that uses 10 vacuum tubes. The IF
frequency is 455 kHz. It incorporates a
noise limiter, an AVC (Automatic Volume
Control) circuit that can be disabled, a
Q-multiplier (a type of active band-pass
filter), and a stable BFO. The power supply
uses a 5Y3 rectifier and OB2 voltage regulator tubes for the B+. It has rear connections for an external antenna and a
headphone jack.
Incoming signals are sent to a switched
antenna coupling network and then to a
variable capacitor that is adjustable on the
front panel via the ANTENNA control to
better match the receiver to its antenna.
After this network, a 6BZ6 pentode acts as
an RF amplifier ahead of the 6BE6 Pentagrid converter and the 6C4 local oscillator. There are two IF amplifier stages, both
6BA6 tubes. The twin diodes of the 6BV8
tube are the second detector and the series
noise limiter. The triode part of the same
tube is the BFO. Half of a 12AX7 dual
triode tube acts as the first audio amplifier
and the other half is the Q-multiplier. A
6AQ5 is the audio output tube. An unusual
feature is the “Audio Response” circuit
that “automatically narrows and widens
the frequency range of the audio output
depending upon the gain required.” There
is no internal speaker. I have an original
Hammarlund speaker and the audio
sounds great, especially on broadcast AM.
The only selectivity control was the Qmultiplier. According to the manual, it
“can provide a means of peaking any signal within the pass band of the IF amplifier.” The degree of peaking is controlled
by the SELECTIVITY control. Hammarlund
claimed that the band pass was adjustable
from 100 Hz to 3 kHz. The FREQUENCY
controls appears to act similarly to a modern-day IF shift control.
The HQ100A is tuned using two large,
black, fluted tuning knobs: MAIN TUNING
and BAND SPREAD. Small flywheels attached to each tuning knob give them just
96 June 2014
Interior view of the HQ100AC.
the right amount of “feel.” A dial cord connected to each tuning knob turns both the
tuning dials and the variable capacitors
that use copper plates. Both the MAIN TUNING dial and the BAND SPREAD tuning
dials are translucent, light gray plastic illuminated by small incandescent lamps
making it easy to see them through the two
arched viewing windows. The band spread
tuning is used to obtain a more spread out
tuning range on 80, 40, 15, and 10 meters.
In addition, there is a special “20BS” setting for 20 meter band spread.
It required a certain amount of finesse to
use the HQ100A on SSB. The AVC
needed to be turned off; the Q-multiplier
turned on; the BFO knob set to the proper
side of the USB/LSB offset; the AF gain
was turned almost all the way up; and the
RF gain was adjusted for maximum intelligibility. It is a bit more rigmarole than a
modern transceiver, but once it is set up,
the audio is very intelligible.
The Hammarlund Legacy
I see a lot of these older Hammarlund receivers for sale at hamfests. For many of us,
these radios remind us of our youth and of
our first years in Amateur Radio. They may
not have all the features of modern-day
equipment and they may not work quite as
well, but learning how they functioned and
how they operated gave us a lifelong interest in radio and communications.
Further Reading
If you’d like to keep reading about Hammarlund, here are some resources:
Ham Radio Museum
The Hammarlund Historian
The History of Hammarlund
The Radio Museum
ARRL, the national association for Amateur Radio® 
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