Tube Amp causing high SWR at Radio when "on"

[Dxrta]

Have seen a simple solution but not tried it. Try a few 5W carbon or thin film resistors in the linear, going from the ground near the input to the input pin that the relay switches the center pin of the coax to while in operation. Perhaps a few 100 ohm in parallel. I think this will help soak up and balance the reflected seen by the radio when in operation. Perhaps you can experiment with the value. Tuning via capacitor is also possible as mentioned. Try to find schematics of other amplifier designs that use such input tuning and copy where they placed it with perhaps some auxiliary components working along side it. I need to brush up on my amp building skills.
As seen in a youtube video. lol

 

[nomadradio]

Good call! This should also reduce the driver tube's apparent drive power level. This is almost always a good thing. A single driver tube is a good match for 1960s radios that would bust a gut to dead key 3 and swing 11 or 12 Watts. And a tube-type CB final stage wouldn't care so much about the SWR.

More-recent radios routinely deliver twice, three or four times that drive level. My usual advice about linears with a single driver tube is to remove it and bypass the radio drive directly to the final stage. The resistor fix is probably a better bet than adding an impedance-matching circuit like you see in a D&A or later Palomar design. That would fix the high-SWR issue, but also have the effect of increasing the drive power to that single tube. Probably bad juju unless the radio is older than the amplifier.

73

 

[Dxrta]

This guy has some great videos that make it easy to understand amplifier design and tuning. The last one I watched was great. Him and the "Gatekeeper" both are easy to follow. Gatekeeper more for beginners.