Acquired 2026-06-06 at the Rockland Hamfest. Serial number __. I do not yet know if the ALC repair was made.

My unit came with a no-name SO-3 clone installed, with the jumpers in place (meaning the TCXO was running in parallel with the original XO). I have removed the jumpers, and will test the characteristics of the TCXO. I am exploring building an alternative TCXO replacement, as SO-3's are expensive and require the original daughterboard be present.

Mark W7MLG made such a replacement in 2017. He used a made-to-order TCXO with a 3v3 LDO and trimmer potentiometer. Not much information is provided regarding the technical details.

• https://sites.google.com/site/markstcxo/
• https://qso365.co.uk/2018/02/installing-a-good-quality-tcxo-from-mark-goldberg-w7mlg-into-my-kenwood-ts-590sg/

Cheap SO-3 alternatives exist, but may be have suspect phase noise or other issues:

• https://www.egloff.eu/index.php?option=com_content&view=article&id=48:ts590s-so-3-tcxo-replacement&lang=en

Potential DDS/PLL based alternatives?

• SiTime Si3521 - this is not sold as a TCXO, but is a TCXO per its functional description. SiTime only states a stability of 20PPM, but I'm still interested in playing with one. The evaluation board is prohibitively expensive, so I may spin my own board if I wish to proceed further.
• Jason Milldrum has done a lot of research, development, and testing into the application of a Silicon Labs Si5351A coupled with a 25MHz TCXO. This is a $2 part that could be coupled with a $2 TCXO. With appropriate filtering this could be a strong contender, and there is already a baseline of using this combination in amateur radio projects that demand high stability.
  • Lots of posts on their blog if you search “Si5351A” - https://nt7s.com/?s=Si5351A