This model is a hot rod with no "OFF" switch for the nitrous bottle.
The driver stage is what's called a 'grid driven' circuit that requires much less drive power than the more-common "grounded grid" circuit found in nearly every other CB base amplifier. This also makes it more sensitive to unwanted feedback problems, since it takes a lot less "leakage" from the final tubes' output power back into the driver to make it misbehave.
The high SWR you saw was from the amplifier oscillating, and putting out multiple extra frequencies besides the one the radio feeds into it.
Those 'extra' frequencies are not the ones your antenna is tuned for. This causes the SWR reading to rise, even though the reading with just the radio alone is fairly low.
The single biggest thing that would serve to settle down this model and make it behave had to do with the coax cable that runs from the Load control to the relay in the rear.
The shield on this coax is not connected in the factory setup. This turns that length of coax cable into a transmitting antenna.
INSIDE the amplifier. Causes a portion of your output power to "leak" back into the input of the driver tube. This causes RF feedback, the source of your unwanted 'extra' frequencies.
Simply adding a ground wire to the braid on that coax at each end has been shown to tame this amplifier at least some of the time. Ground it to the frame or the ground lug of the Load control at the front end, and to the "Antenna" socket at the rear end. Stripping 3/8 of an inch of the outer jacket to expose the braid at each end, then wrapping/soldering the stripped end of a hookup wire will let you ground the other end of the hookup wire. This will work as well as any method of grounding both ends of the coax braid.
Cheapest thing to try first, at least.
And if the clear plastic that insulates the center wire of that coax looks like it has been hot enough to soften and "sag", this will be trouble once it sags far enough to dead-short the cable's center wire to the outside shield braid layer.
You'll just need to replace that piece of coax altogether if this is the case. We got in the habit of using teflon-insulated coax for this purpose. Won't melt from the heat.
Just don't use foam-center insulated coax in this spot. It's even more liable to melt.
73
