Nah, they're tetrodes, not triodes.
Those amps are all set up for Class C and run fairly low anode voltage
(usually); the tank circuit can handle a lot more power, they were built
to transmit continuously without tune drifting.
I've put 2200V on them, and added regulated grid bias and screen
supplies for AB1 operation, and the dual tube models will run >800W
output with a muffin fan on the heatsink.
WB2WIK
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
On Behalf Of Sam Carpenter
Sent: Tuesday, December 07, 2010 10:55 AM
To: 'Glen Zook'; donroden@hiwaay.net; amps@contesting.com
Subject: Re: [Amps] Trying to locate amplifier
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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