Hi Musky,
Let's see if I can clear up some of the mud about that "bias" thing.
I like the AL-80B for a couple of reasons. To start, the 3-500Z is a fairly tough tube. If that one is run right, AM won't destroy it too quickly. The "heat" rating of that tube is 500 Watts. The rating of a 572B is 160. Multiply that times four, and you're comparing 640 Watts of heat rating to 500, about 30% more. Not such a large difference in that sense. This is the basis of Ameritron's OUTPUT rating of "1.3 kW" for the AL-572, and "1000 Watts" for the AL-80B, about 30% more.
An amplifier with four tubes is four times as likely to see a tube go bad as an amplifier with ONE tube. More parts tends to predict more things to break, all other things being equal. A box with one tube SHOULD be more reliable in the long run, than one with four.
The whole "bias" issue has to do with the current the tubes will draw with NO drive power. EITHER of these models will need to have that steady "no-drive" current level reduced to keep the steady AM carrier from overheating the tubes.
Best I can remember, NEITHER of these models has a "Low" or "CW/Tune" switch on them. Older ham linears would allow you to reduce the heat stress when running AM, by flipping a switch that would "turn down" the power level. No such luck on these two models. Besides, very few AM operators want to sacrifice the additional power, anyway.
What gets increased is the voltage rating of the component that sets this "no-drive" current load on the tubes. Both Ameritron models use a zener diode to accomplish this. Changing that part to one with a higher voltage rating reduces that "no-drive" tube current. And the excess tube heat along with it.
Changing the "bias zener" to one with a higher voltage spec will also require using a larger zener. One with a larger wattage rating than the stock 10-Watt (I think) part installed at the factory. This part will now get hotter than the stock zener, if you don't boost its wattage rating to match. We use a string of rectifier diodes in series on a circuit board to accomplish the same thing. Costs more, but lasts longer. That detail applies to ALL legal amplifiers sold to hams, since the factory assumes you will mostly be using SSB. No carrier, no heat-overload risk for them to worry about.
And there's one more little detail about "legal" ham amplifiers that still hasn't come up, yet. No 10-meter band. The larger Ameritron models, the 1200 and 1500 are dead easy to "convert" to 10 meters. You cut a green wire. Other models are not so easy. Those require that you obtain a "parts kit" from Ameritron, and have them installed. My info on that detail may very well be out of date, but that's what I discovered last time this came up a few years back. The 10-meter band is what you would use for 27 MHz. 27 is close enough to 28 that it will work. That's the whole reason the FCC won't let them be sold with that band installed. Too easily adapted to 27 MHz.
Your point about a KLV being overdriven by your radio is well taken. Probably would, unless the KLV got modified. Trouble is, there's an even bigger problem with your description of a driver to use in this "theoretical" setup. Both the Ameritron models mentioned so far require approximately 100 Watts PEP drive. Just to simplify things, we'll round that off to 120 Watts peak. Sure enough, a radio pumping 35 won't do the whole job. Trouble is, the "spread" between what the radio delivers and what the 'big' amplifier needs is only about three and a half-to-one. So, who offers an amplifier that ONLY boosts the radio's drive power by that factor? Nobody comes to mind.
The ratio of what comes out to what goes in is the "gain factor". Most linears deliver a gain factor of at least 7 or 8 to one. The AL-80B is shown as roughly ten-to-one. The gain factor for the AL-572B is roughly 12-to-one.
Your "power gap" between the radio's 35 Watt peaks and the 120-Watt peak drive needed is about three and a half-to-one. Oops. You need a driver that delivers about half the "gain factor" offered by the wimpiest driver you can get.
Modifying a small KLV to throttle down this low would involve cutting the drive level inside, so the radio's power level would get handled that way. Nothing stock you can buy that only boosts the radio by a gain factor of 3.5.
There is one alternative that comes to mind. The larger Ameritron amplifiers offer a gain factor of between 25 and 30 to one. Your DX11 into an AL-1500 would show right around 1000 Watts PEP coming out. Never mind that this is half (or less) what it CAN do. It would take that radio to the thousand-Watt level with no driver, anyway. Not cheaply, but at least you would NOT need to worry about modifying the bias in the AL-1500. Running it at roughly half throttle should be safe enough on AM without having to modify the bias.
The AL-1200 comes close to this level with a barefoot base station driving it, but would be hovering just below the thousand-Watt mark, where the 1500 would be hovering just past that power level with your DX-11B.
Sure reminds me of one of my regular customers. He likes to wheel and deal, trading equipment, buying and selling. More than once, he'll have a large box that he likes, but everything else he has either pumps twice as much as the new box will take, or half as much as it needs. Keeps discovering that nobody sells a box that will only double what you drive into it, take up the slack and make his new setup work like he wants it to.
Just feeding the DX-11B into a AL-1500 or AL-1200 would be pricey, but you'd have one less cabinet on the desktop. And it would never even break a sweat. One more little thought. A linear being run at half-throttle tends to be cleaner than one at full-bore or higher.
Almost forgot the relay. Which 300A and which relays? ?
I can think of five different kinds of relay used in the all of the Palomar 300A versions that come to mind. All but one of those is discontinued and/or very pricey. I'm gonna guess that the relay you need is not the 'easy' one still sold by Mouser and other suppliers.
Size, shape, and the markings on the old relay would narrow things down a bit.
73
.