[Hammarlund] SP-600 and Drift

[Bob Young]

I have my SP-600 going through a good Hammond tranny and an old hifi speaker it definitely sounds better than an 390-A but then again it doesn't sound as good as previous super pros. In the 8 kHz and especially 13kHz position it does sound pretty good though, the highs sizzle but it lacks bass (I know that can be fixed with different bypass caps) but overall the audio is decent. I think my tap is on 130V but haven't checked in a while, when I get the gumption to pull it out of the case I'll check it but it doesn't run hot.

Bob Young
KB1OKL

> Date: Sun, 7 Jul 2013 11:30:38 -0400
> From: ka1kaq at gmail.com
> To: chuckochs at hotmail.com
> CC: hammarlund at mailman.qth.net
> Subject: Re: [Hammarlund] SP-600 and Drift
> 
> 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
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