[Hammarlund] SP-600 and Drift

[Todd, KA1KAQ]

On Sat, Jul 6, 2013 at 11:26 AM, Charles Ochs <chuckochs at hotmail.com> wrote:

> Of course all these old radios will suffer from changes in AC input
> voltage to some extent.The R-390 (dreaded 3TF7)and the HRO-60 (dreaded
> 4H4-C) included current regulator "ballast" tubes in an attempt to minimize
> this problem.
>

Changing the power transformer tap solved it for me. Voltage drops are far
less an issue when the set isn't knocking up against or exceeding its high
end for power input with the associated overheating.

The 3TF7 was originally dropped from the A model during the cost reduction
process as unnecessary, but somehow found its way back in. The simplest
workaround for removing it is a resistor between pins 2 & 7. Something like
47 ohms around 10 watts IIRC.

Audio quality of the SP-600 is very good, although it lacks the power of
> the previous SPs in that it uses a single ended circuit instead of the PP
> audio.
>

Hence the 'anemic' description. The 600 is certainly one of the more
flexible single-ended communications receivers in the audio dept., at
least.


> The earlier versions conformed to the then-standard practice among
> high-end radio manufacturers toward "high-fidelity" operation, which
> assumed operation through some big honking speaker.


And when used as designed, they produce far superior audio to the SP-600 or
really any other receiver with communications grade audio. Not necessarily
good or bad, just another facet of interest.


> I run all of my receivers through simple attenuators to drop the output to
> line level, and then into the switching matrix of my audio console, which
> feeds the two speakers in the corners of the shack. Works like a charm, and
> I get total audio consistency. In this setting, the SP-600 has outstanding
> audio.
>

I'm sure it does. The 75A-4 also has anemic audio, as do the 390 family of
receivers. Adequate for the intended purpose, tiring to listen to over long
periods in stock form. All can be made to sound far better by picking the
audio off at some point like the diode load and running it through an
outboard amp. At that point you're not really using all of the radio but
only portions of it.

Again, it's not necessarily a good or bad thing, it really depends on what
the user is looking for. I prefer to use old gear as designed, and for
casual listening over extended periods, a set with hi-fi output is tough to
beat. The variable IF is the icing on the cake. My bedside SP-100 drives a
12" coaxial EV speaker. SX-62B in the living room is lashed to a Jensen
JHP-52 15" coaxial. Also have an original matching Jensen field coil
speaker that has yet to be tried. It's waiting on a SP-10 that needs some
attention.

OTOH the early SPs can't hold a candle to the 75A-4 for noisy conditions
with its mechanical filters and passband tuning. And few sets have the band
cruising abilities of the SP-600.

For me, it's a simple case of picking the right tool from the toolbox for
the job. If you're limited for space or don't want multiple sets, it comes
down to prioritizing which features matter most. For years my 600 sat in a
rack beneath the R-390 and cost-reduced A model. It got the most use of the
three. Especially after the power transformer tap was moved. The 390 family
is great if you don't plan to do a lot of tuning.

So many radios, so little time/space/money.....  (o:

~ Todd/KAQ