[Hammarlund] SP-600 and drift--

[Todd, KA1KAQ]

On Fri, Jul 5, 2013 at 11:39 AM, Charles Ochs <chuckochs at hotmail.com> wrote:

> A couple of people have mentioned drift in the SP-600.Let me assure you
> that an SP-600 in proper operation condition has about zero drift. I have a
> late model one with the ceramic capacitors, and when I turn in on each
> night to listen to the chatter on 3.875 it is right where I left it the
> night before. Maybe a very slight tweak to zero beat, and nothing after
> that.My suspicions about those sets that drift are that they are probably
> suffering from capacitor / resistor disease, or from crappy replacement
> capacitors, or maybe the tuning capacitor has a bit too much wear, and
> "wanders" a bit as it is heated, or maybe the local oscillator tube needs
> changing.
>

More often than that it's a much simpler cause: improper tap selected on
the power transformer. I had constant drift with my SP-600 years back until
Prof. Locklear reminded me to check the power transformer taps. Sure
enough, the factory 117v tap was selected and probably worked great 10-20
years earlier. But even then my line voltage was between 117 and 122 or so.
Even when the voltage was measuring 117v, every little surge or drop made
it wander. Moved to the 130v tap and voila - once it warmed up, it stayed
put.

The bigger issue I have with the SP-600 is overall audio quality. Not
horrible, but not worthy of the Super Pro name IMO. All previous SPs back
to the mid-30s used a wonderful P-P audio section that would fill a room
with excellent quality audio through a big Jensen JHP coaxial, or field
coil speaker. The 600 is an entirely different beast, and while it's a
dream to tune, it's pretty anemic in the audio dept in comparison. A true
'communications' receiver.

~ Todd,  KA1KAQ/4