[Hammarlund] Old Hammarlunds

[Todd, KA1KAQ]

On Tue, Apr 12, 2011 at 11:23 AM,  <djed1 at aol.com> wrote:

> Just to show how the technology changed, my SP-600 drifted about 12 KHz from a cold start, and the R-390A drifted 0.4 KHz.

And that really is a big point that many seem to miss. The original
Super Pro 200s were a 1939 design that evolved from the earlier SP-10
and -100 models. It's important to keep in mind things like the higher
bands weren't the big draw then that they are now. In fact, the
standard Super Pro covered the BC band to 20 mc only. Only the SX
model, made in much lower numbers, added coverage through 10 meters at
the expense of much of the BC band. Compared to other radios of the
day, the Super Pros were at the top of the pile with the HRO, They
were used through WWII virtually unchanged other than some power
supply upgrades.

A lot changed over the roughly decade and a half since the the SP-200
series was introduced. The SP-600 is an entirely different beast, a
Super Pro in name only. And the R-390 series with the famous Collins
PTO was and in many ways, still is the benchmark for old tube
receivers. Which is why it's important to keep things in perspective
with respect to things like drift, features, and so on.

As Ken mentions and as the manual states, the receiver was designed to
be left on for extended periods to stabilize. It takes a while to
bring all of the mechanical bits into harmony, so to speak. Once it
stabilizes though, it's as solid as a rock. Having the receiver in a
location where it can experience temperature changes (near an outside
door, for example) or fluctuating line voltage wouldn't be desirable.

For anyone who hasn't seen Henry Rogers' great site yet and would like
to read more on the Super Pros, I highly recommend it:

http://www.radioblvd.com/hammarlund_super_pro.htm

Henry outlines many of the issues (operator-generated, in many cases)
that have given them a bad rap over the years. I can verify his
findings, especially using the correct feedline impedance for low
noise operation.

The only trick is bringing them up to spec and using them as designed
and detailed by the manuals. Known primarily as a workhorse, they are
really more the thoroughbred of their day. I love my early Super Pros,
they are some of my favorite receivers. In fact, I use a 1937 SP-100
as a bedside receiver driving a large Jensen speaker in an EV
enclosure. Apparently I'm extremely lucky, as it shows no appreciable
drift from turn on to 3-4 hours or more later.


~ Todd,  KA1KAQ/4