I have seen these come through. I had always assumed that the tubes were
basically 8873 but the size was like the 250. I think there may be a VHF
that had been used for Mobile Phone service at a site across town. You have
renewed my interest. I may have to drive over and look.
N9FUT
-----Original Message-----
From: Glen Zook [mailto:gzook@yahoo.com]
Sent: Tuesday, December 07, 2010 11:14 AM
To: donroden@hiwaay.net; amps@contesting.com; Sam Carpenter
Subject: Re: [Amps] Trying to locate amplifier
Those amplifiers used 2 of the 8560A which is basically a conduction cooled
4CX250B. The lowband versions were rated at 330 watts output and the
highband versions were rated usually at 250 watts output although a few were
rated at 300 watts output. There were a relatively few amplifiers made with
a single 8560A. The amplifiers had huge heat sinks and most did not have a
fan/blower. The tubes were mounted to ceramic blocks which were then
mounted to the heat sink.
If I remember correctly, those were in the highband MPB and MPY stations
(i.e. B93MMPB-3100A) and in the lowband LPB stations (i.e. B91LPB-3100A).
The MPY repeater version was very popular with mobile telephone and RCC
operations.
Glen, K9STH
Website: http://k9sth.com
--- On Mon, 12/6/10, Sam Carpenter <sam@owenscommunication.com> wrote:
Moto did make some very robust VHF tube amps. Most that I have seen come
through the shop over the years have been with a Moto marked conduction
cooled tubes that strap to a very large heat sink in the back. The tubes
looked like 8873 series tubes. The tank was VERY robust and I have seen
people use the RF deck with 8877 tubes. I think these were quarter K
amplifiers but would do much more. I will look around the service manual
archives we have in the shop and see if I can find models and spec's for
you. There were also tube HF amps made. I think they were rated at a K.
Power supply would not do too much more. There is a bit of data on the web
if you google around. I think I found things using Motorola HF amplifier. I
think that is where I saw the conversions as well.
There are tons of paging transmitters sitting idle right now. When I go out
to high profile sites they are just sitting there unplugged. I think the
market fell out so fast that they never picked them up or hauled any away. I
think most of the site owners would gladly have someone haul them away. Most
of the tube units were back-up for the newer glenayre solid state units.
They are pretty sweet too. I think though that the VHF amps were run in
Class C. I think that the HF amplifier started with the letters THD, or THE.
That may help refine the search. I will save this and let you know if I run
across anything.
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