[Motorola] Motorola Tube Amps

Wed, 21 Apr 2004 01:50:56 -0400

Glen/John: My first reaction to Glen's post was (and I am refering to me,
not Glen) "What an idiot" I was thinking conduction and wrote convection.
Doh. Can't believe I never saw an 8560A single ended Motorola amp. But then
I also do not remember working on any 100 watt IMTS stations on
hi-band--only 250 watters. I do recall a 100 watt IMTS Motrac style base
that used an updated version of the UHF BBB pa--100 watt with 4cx250. The
dual 8560S amps lasted thru the Micor series except on UHF where Motorola
switched to the single triodes in a cavity in the mid eighties. 800 MHz only
used the triodes as far as I remember.

On the 8072: The Motorola amp used only the 8072 (Don't believe Motorola
ever used an 8122. correct me if I'm wrong). Well, not exactly--it was a
selected 8072, Motorola had a different number for that .. a 4??? something.
too lazy to look it up. But i do recall that if one used an 8072 in a
Motorola amp, it often would not make full power. But put the selected one
in, no problem. RCA, however, never had a problem making 100 watts with an
8072. Odd, but it was their tube. RCA used the 8122 (as you said, an 8072
with cooling fins for forced air cooling) in the 1/4K UHF "Super
Control-Phone 500". It had similar charistics to the 100 watt amp you
described. Tune it up to 250 watts, and a few hours later it would stabilize
at 175 and run there for months. Retune, same thing. I've been told the amp
would work just fine at 250 watts if one adjusted all the bi-metal
temperature compensating caps correctly. The full preceedure took about 1/2
hour. Preferred the Motorola amps!

While the Motorola 2 tube amps worked well with power to spare, my
experience was when the tubes failed the base would often be found in a no
transmit condition. My two favorite amps, the 4-400 in the Quintron QT-350
Low Band (love the shorting stick), and the single 4CS-250 (conduction
cooled) high band amp in the QT-250 would fade away slowly eliminating many
after hours calls.

Anyway, I do have tech info on the MICOR version of the 2 8560A amp for low
band. John, if you can find any TL? numbers (like TLD-4010A ) we may be able
to help with the frequencies these amps were designed for.--Mike, WV2ZOW

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Glen Zook
Sent: Tuesday, April 20, 2004 5:27 PM
To: [email protected]
Subject: RE: [Motorola] Motorola Tube Amps

Motorola definitely made a number of the "single
ended" 8560A conduction cooled amplifiers.  These were
used in a number of the "upright" base station 100
watt continuous duty rated units from the late 1960s
well into the 1970s.  They were especially popular in
the 60 to 110 watt output highband repeaters that were
used on RCC (Radio Common Carrier) and IMTS / MTS
(Improved Mobile Telephone System / Mobile Telephone
System).

The 8072 is identical to the 8122 electrically.  The
8072 is rated at 75 watts plate dissipation (without
external heat sinking) and the 8122 is rated at 400
watts plate dissipation air cooled.  The cavity that
Motorola used in the 450 MHz base stations and
repeaters helped with the heat sinking and thus
increased the power handling capabilities of this
particular tube.

General Electric used a lot of air-cooled high band
amplifiers using both singe and dual 4CX250 and 4CX300
series tubes.  However, Motorola used very few air
cooled tubes in their upright base stations.  One
notable exception to this was the amplifier used in
the C74BBB, L74BBB, and J74BBB 100 watt (really a
beautiful 90 watt output 450 MHz base station - you
could load them to 100 watts, wait a minute or two,
and they would almost always fold back to 90 watts,
retune, and the same thing!)series which used a single
4CX250B.  Also, Motorola sometimes agumented the air
flow in the old "quarter-K" lowband and highband units
(of which the later versions used the 4-125 / 6155
tubes) with a blower system.

Now, Motorola used all sorts of tubes that were
"cooled" only by the heatsink (thus were a combination
of conduction cooling and convection) like the 5894
and 8643 in various versions of the Motrac and Compa
base stations.  But these are not the tube types in
question.  As for "convection" cooled tubes, Motorola
used all sorts of them from the very early days!  In
fact, up until the Motrac (the driver tubes in all of
the Motrac were convection cooled and the exciter
tubes in the HHT series were convection cooled) series
all of the "normal" transmitters used convection
cooling!  In a few applications, convection cooling
was supplemented with some sort of fan to move more
air.

Glen, K9STH

--- Mike Clarson <[email protected]> wrote:

I do not recall a one tube version of these using the
convection cooled tube--only air cooled. I do recall
the 8072 one tube version for 450 MHz. The basic
design of these 2 tube decks were quite similar thru
the MICOR era. I have some info on the MICOR amps in
30-50 MHz range, so if you do not get a response for
you exact amps, this may help.

=====
Glen, K9STH