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

[Mike Clarson]

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.



-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Glen Zook
Sent: Sunday, October 18, 2009 11:06 PM
To: 'Sandy'; 'Glowbugs reflector'; boatanchors at mailman.qth.net; Scott
Johnson
Subject: Re: [Boatanchors] GB> Is 4657 same animal as the 8072?

The tube is just an RCA 8072 branded with Motorola's part number.  I have
seen hundreds of these tubes when I owned the Motorola reconditioned
equipment center for the south-central United States.  Starting in the mid
1970s Motorola usually just put 8072 tubes in the boxes marked with their
part number instead of having them specially marked.

Glen, K9STH

Website:  http://k9sth.com


--- On Sun, 10/18/09, Scott Johnson <scottjohnson1 at cox.net> wrote:

If a 4657 looks like an 8072, it is probably a 26 V heater variant, or
perhaps pulse rated, or some other difference. Also these tubes are not
> planar construction, they are coaxial.