Transcript Using The Harris Platinum I Amplifier on Six Meters

Converting The Harris
Platinum TV Amplifier
For Use on Six Meters
And A Discussion of Trends in
Solid State Ham Power Amplifiers
D. Hallidy K2DH 3/2012
Background
 Solid State PA’s for amateur use are nothing new- they’ve been
around for decades! Think of the units made by:
 Mirage
 KLM
 Tokyo Hi-Power
 TeleTec
 TE Systems
 The thing about all of these is that they typically only produce
modest power (150-200W is the typical maximum), are fairly low
gain (10-12dB typical using bipolar transistors), and they aren’t
cheap!
 They were designed to provide more RF output power primarily for
mobile VHF/UHF stations, running on 12vdc. So their power
capabilities are limited.
Background
 Technology has advanced! Today, companies have developed LDMOS
(Lateral Diffusion Metal Oxide Semiconductor) devices (LDMOS FETs).
 High gain, can produce lots of power in small packages (20+dB Gain,
Hundreds of Watts to >1kW typical power).
 Typically operate in the 50vdc range, making them impractical for
mobile use, but just fine for home station RF power generation.
 Relatively cheap!
 Some companies (for example Ameritron) have designed products for the
ham using LDMOS devices. The ALS-600 and ALS1300 are examples of
600 and 1300W solid state HF amps they offer.
 Some hams have designed high power VHF/UHF amps using them, also.
We’ll see examples and references to some of them in this presentation.
 Some high power commercial LDMOS amps have become available as
surplus to the hams, too. This presentation is centered around one of
these.
Background
 With the changeover to Digital TV, all broadcasters had to remove their VHF
analog transmitters from service, to change over to digital transmitters.
 Many of these analog transmitters were built by Harris and were sold as the
“Platinum” series of TV transmitters.
 Transmitters ranged in output power from 20kW to 100kW, depending on how
many 1kW modules were installed.
 Very sophisticated units, designed for “Hot-Swapping” failed PA modules, with
many levels of fault detection and protection built into them.
 After these transmitters were pulled from service, some of the modules began
appearing on the amateur surplus market, instead of in the dumpster.
 Two versions exist- low band (Ch 2-7) and high band (Ch8-13). Either can be
converted for 6m operation, but the low band version is easiest.
 Modules were rated for 1kW video service, 24/7 .
 Will provide at or near legal limit output in amateur service with modest drive (~25W).
 Here we will discuss the low band version of the Harris amp in amateur
service.
Harris Amp Specs
 Each module consists of 16 Philips
ON4402H LDMOS transistors connected
in 4 pallets of 2 push-pull pairs each and
combined.
 Operates on 50VDC (as do most of the
LDMOS power transistors in use today), at
about 45A (1500W output).
 Drive for 1500W out is about 25W, well
within range of common 6m equipment.
Where Can I Get One?
 I got mine from Steve W1SMS at
Microwave Update 2011 this past Fall. He
may still have some; he got a quantity of
them from WCBS (100kW transmitter) in
NYC.
 Lance W7GJ has been advertising them
and still has some.
 As far as I know, these are the low band
versions only.
Some Images of The Harris
Platinum Amplifier Module
BIG heatsink!
Fault/operate
indicators
Drawer front, used for
inserting/removing the
module in its chassis
PAY ATTENTION!!!
Inside the module, showing the
four pallets
RF
Output
FET
Switches
to turn
on amp
One pallet, showing all four devices
One Pair of ON4402H MOSFETS
Image Courtesy KB3XG
Where Can I Find Modification
Info?
 John Sortor KB3XG wrote an article (3 parts) in the Mt.
Airy Pack-Rats “Cheese Bits” newsletter in May, June,
and August 2010. This article is very complete and gives
all the steps necessary to convert the low band unit to
6m. He also shows power output achieved, drive and
DC power required, and quite a bit of operational data.
He also discusses cooling at length- good cooling is a
must, as none is provided in the module as it stands
alone (cooling was part of the main Platinum chassis).
He also discusses the power supply requirements, as
well as the need for a high power low-pass filter on the
RF output.
 W7GJ has also written a very complete set of
modification instructions. Lance even tells you how to
combine two of them for as much as 2.5-3kW out! See
the link to his website at the end of this presentation.
Cooling
 The module does NOT include any cooling. Cooling air
was provided inside the main chassis into which the
modules were installed. Therefore, you must provide
plenty of air to the heatsinks on the top of the module.
 From the various articles, it appears that 4-5 muffin fans
above the heatsink will adequately cool the unit, but
SUCKING air up from the heatsink, NOT blowing it onto
the heatsink.
 This forces air past the entire heatsink, instead of cooling only
the area below the fan (which can also cause a hot spot directly
under the fan center).
 KB3XG built a very nice plenum for his cooling fans that is
probably overkill (see image).
KB3XG’s Cooling System
Image courtesy KB3XG/PackRats
End of unit
where “drawer”
front would be
Plenum over heatsink, fans on the side
Cable to fault/operate indicators
W7GJ’s Cooling system
Images Courtesy W7GJ
Power Supply
 See the image on the next page. The amplifier
requires 50VDC at nearly 50A.
 This sounds difficult (read: expensive), but it’s
not.
 Blade Server power supplies are available on
eBay for $38 (incl. shipping!) which are rated for
50VDC @ 57A. These are switchers used in
server applications, and are clean and wellregulated. They operate from 240VAC @20A,
Single Phase. They are new surplus, no junk,
made by HP. The model number is BL20P.
HP/Compaq BL20P Blade Server
Power Supply- 50V/57A
Hardware Modifications
 There are not many mods required- they are:
 DC Power Connector
 The original DC Power/RF Input/PTT Input connector should be
removed and a haevy-duty Cinch-Jones screw-type terminal strip
installed in its place for the DC power connections (see images).
 RF Input Connector
 This was part of the power connector but a BNC or other small
connector can be installed on the end of the chassis very easily (see
image).
 RF Output Connector
 Since the unit was deigned for “Hot-Swapping” and instant plug in, the
output connector is not a threaded type. However, it is the same size as
a Type N and can be easily replaced with a chassis-mount N female
connector which will solder right to the output directional coupler board
(see images).
 PTT Input Connection
 A ground on the violet wire in the original multi-function connector puts
the unit in transmit. This wire can be brought out to an RCA jack or
another terminal of the power connector.
Modified RF, DC, and PTT Input
Images Courtesy KB3XG/PackRats
Added Type N Output Connector
Images Courtesy KB3XG/PackRats
Expected Performance
 Again, it should be emphasized- these amps require no




tuning for optimum performance on 6 meters.
SOOOOO…
Pin=26W; Pout=1475W; Ids=43.7A; Vds=47.3V; Max
temp=61.2oC; Gain=17.5dB; Eff=71.4%
As you can see, these are pretty good numbers- and
these were taken AFTER the low-pass filter was
installed!
The performance numbers listed above are not mine,
they are KB3XG’s. My unit is still a “work in progress”,
but should be complete by Spring.
I highly recommend referring to both KB3XG’s and
W7GJ’s articles for details not presented here.
What Other Choices Do I have?
 There’s another TV amp out there (Canadian)
called the LARCAN. These were also pulled
and made available; with careful searching you
might find one- they are similar in power to the
Harris amps.
 You can roll your own! This is not as ridiculous
as it seems. There are LDMOS transistors out
there that will do >1kW output from 1-600MHz
(Freescale MRFE6VP1K25HR6) for about $200
and there are many articles and folks building
them- see the links at the end of the
presentation for more info.
Popular VHF+ Solid State
Devices for High Power Use
 Freescale MRFE6VP1K25HR6 (1200W out/1-600MHz)
 Articles and kits for both 50 and 144MHz 1kw+ amps
using this device (DUBUS 4/2010 for F1JRD article).
See W6PQL.com for his 144 and 222MHz 1kW amps
using this device.
 Freescale MRFE6VP5600H (500W out/1-600MHz)
 Article and kit for 432Mhz 1kW amp using 2x this
device (DUBUS 1/2012 for F5FLN article).
 NXP BLF578XR (1200W out/1-500MHz)
 No article I’ve found yet, but I’m sure there is one, as
the price is about the same as the Freescale part.
F1JRD’s 2m 1kW Amp
Sources of Info, Parts, Kits,
Complete SSPA’s











http://www.italab.com
http://www.rfham.com
http://bigskyspaces.com/w7gj/HarrisAmps.htm
http://www.packratvhf.com/Cheese%20Bits/cheesebits.html
http://www.w6pql.com
http://www.freescale.com
http://www.nxp.com
http://www.dubus.org
http://www.ad6iw.com
http://www.mmra.org/larcan/index.html
http://www.qsl.net/f1jrd/MRFE6VP1K25H.html