The recent purchase of a 500-watt amplifier required a similarly rated tuner to handle impedence matching chores on my 10-80m dipole. Prior to having the amplifier, my tuner was LDG’s AT100Pro which had no problem tuning the antenna on any band and handled the 100 watts from my K3 with no issues whatsoever.
I should note here that the antenna referenced throughout this write-up is an 80m dipole up 22 meters and fed with 450-ohm ladder line via a balun.
With 500 watts out of the amplifier, it was an easy choice of which autotuner to select: LDG’s AT600Pro, based on the good service provided by its smaller brother.
After installing the tuner & amp, I used it to tune my antenna in the CW portion of all 8 bands at a power level of 10 watts. This was done to allow the autotuner to “remember” its settings for those freqs.
So far, so good.
And no problem at 500 watts…except on 40 meters. After a 20-minute run during the ARRL DX Contest (description here), an aroma in the shack left no doubt that some electrical component was hotter than hell. It turned out to be L3 in the AT600Pro – charred black and smokin’.
An exchange of emails with LDG resulted in a replacement inductor a few days later but I knew I’d need to make changes to the antenna or I’d simply cook this inductor as well. The addition of 7 feet of RG8X going from the tuner to the outdoor balun fixed the problem. The tuner now ran cool on 40 meters at full power.
But not on 20 meters.
The problem had now QSY’ed and a few CQ’s at 500 watts on 20 meters resulted in two charbroiled inductors in the photo above.
I realize that my antenna is asking a lot from a tuner, however LDG’s 100-watt tuner handled things perfectly at 100 watts, yet the 600-watt tuner can’t at 500 watts.
For a moment I considered contacting LDG and asking if they’d let me return the AT600Pro and pay the difference for their 1000-watt autotuner but I doubt that tuner would work either, given the amount of heat obvious in the 600-watt version.
In the meantime, a Palstar AT2K is on its way here.
Looking at the size of the capacitors in the LDG tuner, I’m a bit surprised that it can be considered “rated for 600 watts”. That amount of power would seem to call for something of a physical size more appropriate to the power level.