Marvin Double Hung non-tilt balance tubes

A home owner from Chapel Hill says:
As per the attached photos, the coils spring balance tubes have failed on one set of windows. I need two tubes to fit a 73-74" window. One photo shows the bottom spring clip from an adjacent window.
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Paul from SWISCO responded:
Good day from SWISCO.com. I'm sorry, but, Marvin has exclusive rights to their window springs. You will need to contact their dealer.
A quick learner from Chapel Hill says:
Paul,

Been there, done that! Local dealer stated "Marvin is so bad with service records, you have no chance"! "Best bet was to take a picture and send it to Swisscom as they were the best at finding what will work"!

Other options??
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Paul from SWISCO responded:
Being that you have a wood sash, I'm going to recommend a Series 500 5/8" non-tilt balance with a 17-012 bracket. This has been used by wood window manufacturers since the 1940's.

Since it's a bottom sash, I will need to know the visible glass height in order to determine the balance tube length. If you can, I'd also like you to weigh the window sash and let me know how much it weighs. After you get back to me, I'll give you some instructions on installation.
A quick learner from Chapel Hill says:
Paul,

Images attached with tape measure in view! I would guess window weight of 15-20lbs.

Thanks, Chet
Window size
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Paul from SWISCO responded:
Thank you! From your photos, I estimate your glass height as 34", so for a bottom wood sash we add 3" to make it a S500-37". For a 15 to 20 pound sash, go with the red tip color option. Below is a set of generic directions to help you.

With someone helping you, you will need to drop the new balance in from the top of the sash, screw it in at the top, then let the spiral drop down. You will then raise the sash and, while someone holds the sash in the open position, spin the spiral up to the bottom of the sash. Finally, with our 75-004 tool, give the balance about three turns to charge it and lock it to the end into the sash clip.

Let me know if you have any more questions.
How to Identify a Replacement Spiral Balance
How to Identify a Replacement Spiral Balance
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How to adjust a spiral balance on a non-tilt window
How to adjust a spiral balance on a non-tilt window
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How to choose the proper spiral balance tip color
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