[Hammarlund] SP-600 questions,many questions

[Cecil Acuff]

Hi Steve,

        Congrats on the find....they are very nice radio's...I own 3 now
myself...a JX-14, a VLF and a John Leary...wish I had a truck load of them!
(it's a disease with no cure)

It sounds like someone replaced the output transformer with one having a
lower output impedance.  (8 ohms)  It also sounds like they have rewired the
phono jack on the rear to be an output rather than an input.  If there is
enough level to drive your headphones it certainly is no longer an input. If
it were mine and I did a lot of listening with phones I would reroute the
wiring that goes to the phono jack to the front panel headphone jack.  It
may just be paralleled with the speaker output terminals on the rear panel.
If it is you may want your headphone jack to break the speaker feed so the
speaker goes quiet when the headphones are inserted.  Pretty easy to do.
Not quite sure why you get an output that is much lower at the existing
headphone jack though....I will have to look at the schematic and see how it
was originally wired...I would have expected it to be at the output of the
output transformer...whatever it's impedance.

You mentioned "almost" all the caps replaced.  You might want to consider
going ahead and finishing the job....if the remaining caps are electrically
leaky they could eventually damage the power supply.  Keep an eye on the
power transformer and filter choke temperatures.  They should never be so
warm that you can't comfortably place your hand on them for extended
periods.

Lastly it sounds like an alignment might be in order.  You didn't mention
how far off the dial was at it's worst point.  It is reasonable to expect it
to be close and fairly linear...meaning the error should be fairly constant
across the band you are on.  If you are accustom to digital frequency
displays...it will take some getting use to...the accuracy can be improved
by using the logging scale to allow repeatability of tuning.  I think it is
explained in the operators manual...I'll have to look, but first the
alignment needs to be close.

Hope that helps..

Cecil Acuff


----- Original Message -----
From: "steve maus" <smaus@io.com>
To: <hammarlund@mailman.qth.net>
Sent: Tuesday, April 29, 2003 11:26 AM
Subject: [Hammarlund] SP-600 questions,many questions


> Greetings all,  After a year and a half of swl an a dx-398 I began to
hunger for a more
> substantial radio and found one of these beauties at a local hamfest, a
JX-1  ser.#4646,
> in good operating cond. "with 'almost' all the caps replaced."  I, of
course love it, but I
> have a few questions.  On the audio output strip the 600 ohms is scratched
out and 8
> ohms marked in. The radio sounds good, esp. strong signals, but the former
owner didn't
> know what had been done, and I wonder, if the radio were still in the
original 600 ohm
> config. would it be obvious to an ignorant newb like myself? Looking
underneath, no
> additional transformer has been added between T-7 and the speaker
terminals however
> T-7 has only 4 pins whereas every photo or schematic I can find shows 8.
And
> headphones. A pair of 600 ohm phones plugged into the front panel gives
only a faint
> signal. I got a "600 to 4000 ohm headphone transformer"  from Fair Radio
and that
> maybe doubles the volume but it's still quiet and kind of washed out
sounding. The
> previous owner thought the terminals marked "phono" on the back of the
radio were for
> headphones but I see, cruising the online manuals this was for a
phohograph or other
> audio input. Just for the heck of it I touched the headphone plug across
those terminals
> and darned if there wasn't a good signal. Could that be the case if this
was still functioning
> as an input?  Would it be bad form to attach a headphone jack here?   How
about
> attaching it at the speaker terminals, perhaps with another volume
control, and would the
> headphones provide an adequate load for the amp? And one more question.
The
> frequency displayed by the dial matches that received pretty closely
through the middle of
> the HF bands but is off a bit by the time I get to New  Zealand at
17.675Mc. or CHU at
> 7.335 and off alot should I wander down to WWCR at 3.210.  Is this
indicative of any
> particular weakness or need of any sort of tune up?    Thanking you in
advance, Steve
> in Texas
>
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