Since getting back on the
air in South
Australia ( VK5 ) I have generally run fairly low power (25- 100Watts)
on 144MHz but
while living in Alice Springs I had built or converted serveral valve
amps for 144MHz. I have through the kindness of others been able to buy
back my original single 8874 triode amp but have not been able to get
up the courage to excite the HT on that amp, it requires a bit of work
around the HT rectifier and capacitor bank, so in the main part have
not had an amp to use. During the work on my LARCAN modules for 50MHz I went wild and bougth an LDMOS module from ITALAB in Italy but swore I would wait until the LARCAN was going on 50MHz before I dedicated any time to the new 1KW amp for 144Mhz. Around this same time the NEC V360 amplifiers from a Channel 5A TV transmitter started to appear in local shacks, so I asked about getting one and in due course one appeared. I am not sure why I did this as I had the LDMOS module there on the shelf waiting to have DC put onto it. Oh well it is done now, maybe I will use it for something or give it to some one who needs an amp. Well a need arose where I knew it was going to be benificial to have a bit more power and be able to off load the heat from the ICOM 275 multimode into the external amp so the evaluation of what needed to be done had to become number one priority in March 2014. |
Power Supply
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Drive power, too much drive power
As is typical in these
sort of amplifiers the input level needed to drive them is very low and
presents a problem of how to disperse the extra power from a modern day
transceiver to meet the low power level needed. In the case
of
the V360 if you look at the internal layout you will see there is a
multi stage driver stage to take the low input power up to a level
required by the output stages so why go down in level then back up
again? When talking with Colin, VK5DK he alerted me to this
option and had already converted his V360 in a similar fashion. {Edit -
Col had actually injected one stage earlier than me to get more gain}
Thanks
Colin, you saved me a lot of trouble. |
V360 P.A input splitter, high level drive goes in at the bottom of this after you lift the hard line coax's off |
Connections to the V360The V360 uses a DC connector on its rear panel that I have not seen for many years and have no idea where you would source one to use for the DC input as well as control and alarm voltages out. Having no hope of getting one of these it seemed obvious I needed another way to get power into the module. After some poking and proding I decided to drill two holes in the rear panel to allow some heavy DC leads to be connected.NOTE: While investigating the centronic connector I undid the screws for the socket on the V360 and pulled it forward to see what was connected. This led to the two wide tinplate steel strips that come down from the PA's deck comming into contact and they did not seperate after I pushed the connector back in. I was quite shocked to find the module now had a dead short on the B+ to ground. Sigh, nearly another tradgery as I was about to turn the power swtich one to do some tests. |
Original rear panel of the V360 showing the muti fuction DC connector |
RF out of the V360Getting power out was very easy, after deciding on the high level drive configuration, I piped in 5Watts from my FT-817 via a coax fly lead, applied the needed 28V and connected a power meter and dumy load the output connector (shown in the photo below). I was immediately rewarded with over 50Watts of output power and the Alarm LED went off now that there was some output, time for a cuppa to evaluate my victory : -) |
part of the V360 front panel (top 1/3 rd) showing the standard output connector and the Alarm LED |
V360 documents |
Looking across the RF section of the V360, output is to the right. Oh the big blue things are circulators (black magic) |
Looking down on the otput stages of the PA, output is at the top where the two blue circulators meet |
Where to nowSince my initial run up and tests, I have been using the amp on SSB and digital modes. It needs no extra cooling in SSB or CW operation and gives a smooth 300W PEP. Digital modes can be run at 200W out (according to my Bird 43) without any undue stress but the module could do with some fan cooling at this level. This has all been done in Winter, so in summer a fan is definitely warranted for any digital mode in a non air conditioned shack. |
Yet to do1. remove BIAS on Rx to reduce idle current / heating on standby2. fans on heatsink for summmer / digital mode 3. tidy my mounting of the coax relays 4. fit a SWR / Power out display to be driven by the internal coupler |
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This web page was last edited on 6th May 2014 by vk5pj |