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So I have an old 9 tube base amp (PAL 750b). The radio has an SWR meter built into it and I have an external watt/SWR meter at the antenna side . When I key the radio with the amp off or on stand by, the SWR at radio and meter are nice and low.
But when I put the amp on, the SWR in the radio jumps to 3:1 how ever the SWR at the external meter to the antenna remains low. In fact the radio cut the transmit a couple of times almost immediately when it sensed the high SWR.
Obviously sound like something inside the amp. This thing is quite old but I know it has been recapped in the last few years.
Any idea what causes that high SWR when the amp is fired up?

[QUOTE="Brian G, post: 766363, member: 60108"] So I have an old 9 tube base amp (PAL 750b). The radio has an SWR meter built into it and I have an external watt/SWR meter at the antenna side . When I key the radio with the amp off or on stand by, the SWR at radio and meter are nice and low. But when I put the amp on, the SWR in the radio jumps to 3:1 how ever the SWR at the external meter to the antenna remains low. In fact the radio cut the transmit a couple of times almost immediately when it sensed the high SWR. Obviously sound like something inside the amp. This thing is quite old but I know it has been recapped in the last few years. Any idea what causes that high SWR when the amp is fired up? [/QUOTE]

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