[Hammarlund] Ronald McDonald's SP-600

[Richard Knoppow]

     If its a JX-1 and original it probably has "bumble bee" caps in it. 
Those must all be replaced. There are about 42 of them. All military 
SP-600's were rebuilt with disc ceramic caps but I would use modern 
plastic film caps now. Some caps are fairly well hidden. I would also 
replace the multi section electrolytic filter cap. I think Hayseed 
Hamfest has an exact replacement. Also look out for leaky electrolytic 
bypass caps in the AVC. Its a lot of work but worth it and you will 
never have to do it again.
     Note there is a special tool for removing the coil modules from the 
tuning unit (lost a word here). They can be removed without it but the 
tool makes life simpler. Very rare.
     In order to replace the caps you must remove the RF deck. Not 
difficult but be very careful to keep the coils at half-cock or you will 
damage the spring contacts when you replace the deck.
      Its important to align the dial pointers correctly, the moving 
mail pointer is made like a gunsight to eliminate parallax. It should 
come to just above the separating line of the different bands. It should 
run straight up and down. When correctly aligned the frequency 
calibration is very accurate, maximum error about 0.25%.
     Check the second conversion crystal for frequency. If its drifted 
it will cause an error in the calibration of the double conversion bands.
     DO NOT ever bend capacitor plates. I have replaced main tuning 
capacitors in two receivers where someone had bent plates because they 
didn't know how to align the receiver.
     Let us know how this project goes.
     The caps in most of these were the Sprague "Black Beauty" caps. 
These were supposed to be very high quality but there was some 
production problem. Many of them, especially the oil-filled ones, have 
cracked casings and all tend to be very leaky. Just replace them all.



On 3/7/2026 11:15 PM, Kenneth G. Gordon wrote:
> On 7 Mar 2026 at 22:56, Richard Knoppow wrote:
> 
>>       There is a handbook for the Northern Radio version of the SP-600 at:
>> <https://www.rigpix.com/hammarlund/sp600j_northern159_manual.pdf>
>> The schematic is in the same file and at:
>> <https://www.navy-radio.com/manuals/northern_sp600_schem.pdf>
>>    It is essentially identical to the Hammarlund SP-600-JX 17.
>>        There is also a modification work order showing how to install the
>> gain trimmer and a dropping resistor for the dial lamps. The dropping
>> resistor became a stock item on the JX-17. I've installed a couple of
>> them, they do extend the life of the dial lamps considerably, the SP-600
>> is a lamp eater. I think this is at BAMA.
>>      Changing to LED's helps a lot more and gives more uniform
>> illumination to the dials.
>>       I will repeat that I think there are a lot of SP-600's out there
>> which work but are really broken and do not perform up to their
>> capabilities.
> 
> Yes. I agree. In fact, I own one, a -JX1, which I have never yet turned on, and won't until I
> can properly restore it. I LOOKS as though it was never used.
> 
>   They are really quite remarkable receivers.
> 
> I most certainly agree.
> 
>>       FWIW, you can improve the sound on broadcast stations by running it
>> in Manual RF gain. The AVC is too fast resulting in a lot of low
>> frequency intermodulation. Just try it and see how much cleaner it
>> becomes in manual.
> 
> Thank you for the info.
> 
> Ken W7EKB

-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998