If the tubes are good, you can remove them and sell them for double the price you're paying for the box.
If they aren't good, you're wasting good money to buy it.
Have a VERY close look at the filter capacitors, and run the tubes through a good-quality tube tester before reaching for the money.
The thing is between 25 and 30 years old, so there will be age issues if it still contains original electrolytic capacitors.
How much power it should show has a lot to do with the radio AND the wattmeter in use. Not all versions of the 750 are the same, by a long shot.
Some versions of the 750 were designed to match a tiny radio, by modern standards. If you can't get it hooked up to try so you can see/hear what comes out of it, the thing is a pig in a poke.
Some of these left the factory not set up just exactly right. If you do a check-out run into a dummy load, watch to see that the gray plate surfaces inside the tubes don't "cherry" or show a red glow after you're keyed for 20 to 30 seconds. If they do, you'll need to have the bias, and maybe some coil adjustments inside "fine-tuned". If only one or two of them does this, it's a sign that the tubes in that section are not well-matched. Typically mixing new and used tubes will cause some but not all of them to "cherry up" before you have been keyed that long. And if it shows too much carrier even with the radio turned down below 2 Watts, you have one of the "too-hot" versions of the 750.
Think about buying a 1978 car (turbocharged motor) without being allowed to start the motor or drive it around the block. It's not JUST the miles, it's the years, too.
The 750 really is a radio hot-rod, so if it blows a tire, you could hit the wall on the straightaway. Lots of smoke and broken pieces.
73
