[Amps] Trying to locate amplifier

[Sam Carpenter]

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 at yahoo.com] 
Sent: Tuesday, December 07, 2010 11:14 AM
To: donroden at hiwaay.net; amps at 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 at 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.