[Hammarlund] Ronald McDonald's SP-600

[Kenneth G. Gordon]

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