[Hammarlund] List

[Richard Knoppow]

   SP-600 desk cabinets are very hard to find. The JX-17 is the 
diversity version, based on the modifications made by Northern Radio but 
built by Hammarlund. The main differences are the connections for 
external oscillators. A further mod was made by installing a bias pot in 
the first IF to provide gain trimming so that all receivers in a 
diversity set match. Not needed if the receiver is used as a stand 
alone. The pot is mounted on the front panel in place of the dial lock. 
The BFO is also slightly different with fixed bias and level, no level 
pot on the back. When used with a diversity combiner or an SSB adapter 
the internal BFO is not used. The 17 is the one with the RED knobs on 
the front.
    It also has a mod to install a dropping resistor in the line to the 
four dial lamps. I put the same resistor into my other JX, a 21 I think 
it is but am not sure because the original cover for the tuning unit was 
missing. If you use regular incandescent dial lamps the dropping 
resistor will extend the life maybe five or more times. Worth doing. 
Instructions are on the web along wiht the plethora of stuff on these 
receivers. I replace the dial lamps on mine with LEDs. Give more uniform 
illumination and probably unlimited life.
     Even though the tuning capacitor is slotted please DO NOT bend the 
plates. They are meant to be straight and you will never get the 
calibration or tracking right if you bend them. However, do check to see 
that the stators are centered in the rotor. Each stator is held by four 
clamp screws. It should be exactly centered and parallel with the rotor.
    I am not sure how much difference it makes if the second converter 
crystal is off frequency but if you have trouble calibrating the upper 
three bands I would check it. I have not quite reasoned out if it will 
affect the calibration but think it might.  The JX-17 was also made with 
ceramic caps at the factory so does not usually need the mass changeover 
from the "bumble bee" paper caps in the earlier sets. However, do check 
the canned electrolytic caps, they can go bad. In my receivers and in my 
AR-88 I just mounted new caps on terminal strips. I find trying to 
restuff canned caps very frustrating and no one is going to look at the 
interior of the receiver.
    I have had trouble with microphonics of the HF oscillator. I have 
not found a sure cure for this, its not the tube. Varies from receiver 
to receiver. I have never found the answer.
    We have a couple of real experts on this list, Chuck Ripple and Les 
Loklear in particular so anyone undertaking a rebuild has a very good 
source of advice.
    These are very fine receivers which have a bad reputation because 
they will work fairly well even when sick.
    They are also IMO beauty contest winners.
    Another note; if you used one for high fidelity broadcast reception 
you will get better quality by taking the audio off the detector load 
which has terminals at the back, and going to manual RF gain. There is 
feedback in the AVC at low audio modulation frequencies causing some 
intermodulation distortion. Going to manual gain eliminates this. 
Audible even with the internal amp.
    If you run it without a cabinet it should have a bottom cover. Just 
a sheet of metal with screw holes in it. There was also a top dust cover 
in rack mount units, I think also not hard to make but I've not tried 
that. The brackets inside the chassis are slightly different for cabinet 
mounting and rack mounting with a bottom cover. To put a bottom cover on 
a cabinet model you may have to make new, slightly longer, brackets. 
Wirth doing because the back screws for the cabinet are important due to 
the weight of the radio.
     I am writing too much, enough!

On 11/22/2023 3:49 PM, manualman at juno.com wrote:
> The only Hammarlund equipment I still have floating around here is a
> HQ-170A VHF, a SP-600 JX17, and a HR-10. Everything else is gone to new
> homes.
> And two Premier still in the box cabinets for SP-600's and similar sized
> receivers, that I bought when there was that mass order back around 2000
> to the manufacturer, by Cal (I think that was his first name).
> 
> Pete, wa2cwa

-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998