[Boatanchors] GB> Is 4657 same animal as the 8072?

[Glen Zook]

GE had at least 1 450 MHz base station that used the 8072.

The RCA problem sounds like a similar problem with the 100 watt Motorola J74BBB series that used a 4CX250B.  You could tune it up for 100 watts output but in a few minutes it would drop to about 90 watts.  Retune it for 100 watts and then it would drop to about 90 watts again.  Everyone that I knew just let the final run at 90 watts.

Glen, K9STH

Website:  http://k9sth.com


--- On Mon, 10/19/09, Mike Clarson <mclarson at rcc.com> wrote:

Just some additional comments: The 4657 was supposed to be a specially selected 8072 for use in Motorola equipment. I have used 4657s in RCA and GE (Did GE use this tube? I seem to remember using one is some sort of GE radio) radios with no problems, and 8072s in MOTRACs (Mobile and base) and they all operated to spec, so I suspect Motorola just didn't want to use a part with the name of another 2 way manufacturer. 
 
8072 vs 4CX250 series. First, is RCA didn't design the 4CX250. Also, 8072 was conduction cooled, and was designed to be more rugged in mobile applications and had a specified heater voltage of 12-15, perfect for mobiles. RCA also designed it to be LOW COST with a low cost socket. I recall buying NEW 4657s from Motorola parts, at the service shop (NSO) price of $20 in the late 1970s. 
 
8072/8121/8122: As far as I can tell, they are all pretty much the same tube internally. 8072 is conduction cooled, rated for 100 watts plate dissipation when used with simple cooling techniques. One could, with more advanced techniques, dissipate up to 300 watts! --According to the Tube Manual. The 8121 is forced air cooled and designed to run at about the 100 Watt dissipation level while the 8122, also forced air cooled, could dissipate 400 watts. RCA used one of these in their 250 watt 450 MHz base stations. It was an odd setup where the cavity had a bunch of bi-metallic temperature compensation adjustments and was a real pain to tune. It would do 250 watts with a fresh tune up, but would taper off to 175 watts in about a week and stay there. One could retune it to 250 watts, but a week later, 175 again. Didn't seem to hurt the tube.