Owners of Jelco arms?

You might want to try NERVE Audio, I have 2 Jelco TK-850M tonearms and on both of them I use the Axon 24 Tonearm Cable, one with the 90 degree din plug and the other with the straight plug. Axon 24 Tonearm Cable – Nerve Audio On the one with the straight plug he even custom made it for me with a Zavfino 1877 TAD-3 Tonearm Connector.These are great cables that really bring out all the nuances on your vinyl. Just send Curtis an email and he will be happy to help you..

I'm using the Jelco JAC 501 cable with my TK-850L MKII tonearm. These cables are sturdy and well made, uses high quality parts, and very neutral sounding in the few months I've had them. Unless you're wanting more highs or lacking something in your system and intend to use cables as a tone control, I don't see the point of spending more.

I’d like to upgrade my cable from the Jelco cable, considering a Synergistic Research Foundation cable. Anyone familiar with them?  For Jelco Tk-850l. 

Different systems, different ears and subjective listening preferences perhaps. Funny, but I found the high frequencies to quite possibly be the one area in which the Audio Sensibility Impact cable most showed its superiority to the Jelco cable (sounding much more natural, almost like a layer of grit had been removed) but it was pretty noticeable pretty much from top to bottom. No loss of transparency or spatial cues here. Just more music.

I'd be inclined to agree with a review of the AS cable posted below; that reviewer
essentially heard what I heard in terms of the AS vs. the Jelco. And the Jelco I was using had also been cryoed and burned in on an Audiodharma cable cooker and had been improved over the stock Jelco cable IMO. 

So yes, probably a good idea for the OP try try both cables from Steve. 

https://wallofsound.ca/audioreviews/a-truly-outstanding-120-phono-cable/

@hdm Hi again. On both the AS phono cable and Yamamoto headshell, the dealbreaker for me was loss of high frequency detail and air which impacted transparency and spacial cues, and ultimately the soul of the music. The AS cable had no redeeming quality over the Jelco 501. The HS4 had cleaner mid bass but that wasn’t enough to redeem it. Perhaps it has to do with my system but I would counsel the OP to try both cables and make their own decision. 

I think Turntable Labs has JAC-501 cables.  The cables are pretty good.  

Turntable Labs was a little slow shipping, but they are in NYC and it was during the full lockdown, so they are forgiven.

Another vote for the Audio Sensibility. I use their copper version (2 in fact) and found it to be noticeably better than the the Jelco cable-I used the 506 balanced
version for many years. 

I described the differences that I heard in a review of the cable at Canuckaudiomart linked to below. My assessment of it was very different than
noromance's but we have also been on different sides of the fence on the Yamamoto HS4 headshell as well-we must have different listening priorities/preferences. 

If you search there are also other reviews on the Audio Sensibility cable that 
are a bit more recent at Canuckaudiomart as well. 

http://www.canuckaudiomart.com/forum/viewtopic.php?t=45784

@jond Yes.

Didn't I just read Jelco was shutting down?

Morrow cable I think it's still having their 45% off sale. I just picked up a PH-4 cable for my jelco 750 e b and it really really opened up the sound

probably is a din version of this

https://www.ebay.com/itm/Ortofon-6NX-TSW-1010R-Tonearm-Cable-RCA-RCA-Terminal-1-2m-Japan-NEW/123323699887?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I linked to AS above. I did try their phono cable with the OCC wire and the Jelco one was better. Passed more detail and air.

try audiosensibility in Toronto. He is a Jelco dealer, but they make their own cables as well.

Jelco JAC 501. It's clear and transparent. Around $120. Try George Merrill or here.
I notice they’re getting more expensive as Jelco closed.
Don’t be tempted to settle for cheaper 101 version. It is inferior.