[Amps] 4-1000A Vs 3-1000Z

[W0YR at aol.com]

One of the reasons the 4-1000-A became so popular was the easy and low-cost 
availability of "pulls."  Broadcast transmitters used the tube in the 50s and 
60s (some still do) and there were many which were working fine but which 
were retired after a certain number of hours in service.

That is how I obtained the first five 4-1000's I had.  

On the other hand, the 3-1000-Z was used in far fewer commercial amps and if 
you wanted one you had to shell out over $400 to get one.

There may be other reasons, but these are the first that come to mind.

73

Mike
W0YR