[QuadList] Headwheel blower questions

[Don Norwood]

I recently dealt with a problem that led me to discover something I had never thought much about before, the various schemes used to provide cooling air for the video headwheel, and what the requirements were for cooling the headwheel motor. It's something that had just always worked. Aside from cleaning filters, I never thought much about it. Now I realize that there was an evolution in this process, and it's caused me to wonder about several things.

The original head blower on the VR-1000 was an incredibly heavy-duty device. It was built like a vacuum cleaner inside of a very thick-walled canister. The same assembly was used on the VR-1100. If you measure the vacuum at the head-cooling ports on the transport plate, you'll see that it pulls about 20” of water! 

By comparison, measuring the cooling port on a VR-1200 indicates only about 2” of water, and then, there's the AVR-2 with no head blower. I haven't checked the AVR-1 or AVR-3, but I don't think they used any cooling air either. Of course, the AVR series machines use different head assemblies than their predecessors.  RCA machines had fairly substantial head blowers too, from the TRT-1 up through the TR-70. Don't know what was done in the TR-600.

I have some Mark-3 heads which I never noticed running hot, but then they were run on VR-1100's with the massive air flow. All newer 1100's were spec'd for the Mark-10 head, and there was obviously no cooling problem with that combination!  But the VR-2000 and 1200 still had warning lights for the cooling air, even though the flow was much reduced. 

So, did the original headwheels really run hot and need the cooling, or was this just “good engineering practice”? And a service question too..... does anyone know the proper setup procedure for the airflow warning switch in a 1200?  I have the procedure for the 1000/1100, but can't find anything for the 1200, and they are very different.

Don
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