I have a replaced the fan on my TM506 with this fan: ETRI LV 141 1700RPM 55CFM 115V 8W. Link to data sheet here: This particular model is very quiet.
The higher speed models listed on this datasheet are noisier fans, those models are typically used on CNC machines to cool the power supplies and electronics.
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Michael Lynch
Dardanelle, AR
Michael W. Lynch