Discussion in 'VHF/UHF - 50Mhz and Beyond' started by N6YFM, Jul 26, 2018.
Tell us more please!
I buy junk on Ebay & repurpose it. Just like the old days & tubes, but with LDMOSs.
At the moment, on pallets, I have:
4 MRF 574s
12 MRF 154s.
All Ebay junk that actually works. Not a single bad pallet.
I also have 5 (Was 6) of the 1800W 65VDC LDMOSs. They will give me 160M-70cm at legal limit, waercooled & excited by an SDR setup, all in an old MAC G5 case.
I got junk...
Back in the 1970s we ran a KLM mobile amp on the 146.94 repeater in Holyoke, MA. That machine was very active, and the KLM mobile amp was in use for three or four years before being replaced by a GE power amp.
The only problems were a poor soldering job on the collector tabs, easily fixed, and the amplifier not liking looking into a duplexer that presented a reactive load off frequency. A ferrite isolator fixed that problem.
The amp had a squirrel cage blower running air over the PC board, and set of muffin fans on the heatsink fins. It did a good job at the 90 watt power level. The last amp at the site was a custom built repeater amp from Henry Radio. I still have that old KLM amp in storage... it was last used about 10 years ago on my 146.715 machine until being replaced with a commercial Motorola repeater system.
Move air, keep the board and devices cool and even a good mobile amp with do 100% duty cycle when run conservatively.
I assume if you used a "mobile amp," you bypassed or removed the relays so the amp would always be in the "transmit" condition without relays clacking. They were the "weak link" in almost all SS "brick" amplifiers if put into repeater service.
No. The relays were left operational. They were constantly energized and not keyed so we could be
able to bypass the amp via the control link in case it failed. The repeater was at a remote TV transmitter site that
was a bear to visit in winter.
I'm surprised the relays lasted, energized all the time. They're not rated for that.
I found to use the old KLM PA10-140Bs and such I had to get rid of the relays and also add a very good feedthrough filter for the +14V power lead to prevent radiation from the power cable. Rather than add fans, I took out the PCB and mounted it to a solid copper heat spreader, and then bolted that to a much larger heatsink. No fans, passive cooling but probably 4x the surface area.
Darned thing lasted 25 years.
I think Jim Decent went out of business a few years back. He was known for his gear. Especially his amps.
His advertising slogan was "If you need an amp, make sure you get a DECENT one!"
Mirage, MFJ, others are ok, if your budget minded, try out TE Systems amps, have 2 now, error of caution with
any solid state amps. Do not skimp on power supplies, I carry an overage there on supplies, then there is no fear of
straining your amp.
Preamps on TE's are ok, but i like an outboard preamp at the antenna for maximum effect. You planning on MSK144
ops or just usual cw/ssb ops on vhf?
Also, spend good money on feedline, makes a difference on weak sig work, I promise you will notice a difference instead
of Walmart brand X coax!
good luck, keep us posted to your station.
73's Steve WD5HNI ....
I recall a gentleman, I think he's SK now, who lived north of Enid, OK who had a 2m Henry kW and maybe a 6m version as well. Rather impressive.