"I thought it'd be a great opportunity for people to branch out and do some networking," Ms McGeorge said.
"We musicians sometimes have the reputation of being rogue traders who are out for ourselves -- but it's good to help each other out."
As the name suggests, musicians come together and "jam" -- improvising without preparation or predefined arrangements.
Attendees also share tips on songwriting and instrumental craft, and pass on the contacts they need to arrange live shows.
Some are even working on collaborative projects, despite having only met recently, Ms McGeorge said.
"It can be hard when you're starting out and you don't know who to call and how to put yourself out there.
"But we've had a few bands form, and people getting booked for gigs, just by the guys swapping numbers.
"It's Networking 101."
During jam sessions, attendees have played various styles of music, including rockabilly, blues and experimental rock -- with sometimes as many as 10 people playing on stage.
Musicians have various levels of experience, from UCOL students to the big names on the Wairarapa circuit, such as Stefan Brown, Andy Eldred, "Dr Rob" Maunsell, Masterhuna drummer Brendan Hullena and Koia singer Tirau Te Tau.
"Some of the more seasoned musicians have been passing on their knowledge to the younger ones, which is nice to see," Ms McGeorge said.
With people travelling from Wellington, Whanganui, Hawke's Bay and Taupo, the jam nights have so far boasted up to 40 people.
"But we'd love to see them grow. People have really enjoyed themselves -- it's been a bit of a secret midweek musical release. But we don't want to keep it a secret."
Jam Night is held on the last Wednesday of every month, starting at 7pm. The next event will be Wednesday July 29. Contact Holly McGeorge on 027 850 2518 for more information.