Marti frequency control module temperature

[ChuckG]

Marti used these in their STL transmitters. Basically a heater module strapped to the crystal with a transistor controlling the heater current.
Unfortunately I can't get into the heater module without destroying it and these things are unobtanium from BE.

Anyone know roughly how warm/hot these should run? I have one that is operating but is far hotter than I remember them being. Not sure if there is a temp control element that has failed, or my memory has failed.

[kcbooboo]

A Moseley PCL6000 manual claims (in several places) their crystal ovens operate at 65C. I would think they have to run at slightly above the maximum temperature the unit is rated for, such that the crystal will always be higher than the highest ambient operating temperature expected. That manual says that's -20C to 70C, but perhaps the 65C is still high enough to get it on frequency. Perhaps the Moseley units are similar.

Bob M.

[RGORJANCE]

Chuck:

Your question and Bob's comment got me scratchin my head. Did some real quick googling and found this. It might help.

"For instance, a crystal may be specified as having a frequency tolerance of ±50 PPM @ +25°C in a frequency stability of ±50PPM over an operating temperature. This would give the crystal an overall stability and tolerance budget of ±100PPm or .01% potential frequency error".

Fossil

[ChuckG]

Well, I cheated and used an Airpax thermal control in line with the runaway heater element. Keeps it at just under 90F. I figure that will be the highest ambient temp it will ever see inside a studio building. If the temp jumps above that I'll have the firemen unplug it.
The frequency does stay within tolerance from 60F to 100F without any crystal heater at all, so I'm not sure what I bothered for, other than satisfying the OCD.

[TPT]

Don't remember what the equipment was, but I remember using a Christmas tree bulb to replace a failed heater in some kind of STL transmitter.

Worked fine even though the equipment rack was in an unheated room.