The YU-106 appears to be a just 3-4 wraps of 3/8"? copper tubing wrapped around the anode.?
The YU-191B? is the real deal, with the coffee can around the anode.... just like all the other water cooled tubes.??
2-3 years ago, several appeared on the used market..... and several? hb HF amps were built using them.? ?I forget what the required water flow rates were.? The folks were using distilled water, external pump, external air cooled radiator ( shrouded between fan and radiator), and once they got the cooling optimized, the amps worked very well.??
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The beauty was...... there was no noise, nor heat in the shack.? Some of the folks had the hot air from the? radiator exhaust? routed to the outside in hot wx.? ?And routed to the inside in winter.? ?As long as no leaks anywhere, and safety interlocks used, it works fine.? ?IE: with loss of water flow, reduced water flow, water too hot entering the tube, everything shuts down asap, including opening off key line, and shutting the fil off.
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Note forced air is still required to cool the fil.? 7.5 vac @ 50 amps =? 375 watts.?
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It's a superb tube....and afaik, it's still rebuildable per Econco. .?