A My guess would be a problem with the amplifier-input circuit. A lot of older amps used tuned inputs that were switched as you changed bands. Over time, the values of the coils or capacitors can change, resulting in the input impedance changing. If you have the manual for the amp, take a look at the schematic. If the input circuit has adjustable coils or capacitors, you can try tweaking them for a better match. You could also use an antenna tuner between the rig and the amp, although you may still experience some power loss in the input circuit after the tuner. (Remember: An antenna tuner does not change the SWR at its output. See Figure 2.)
Although Gonset is long out of business, you might still be able to obtain a copy of the manual if you need one. To find a source for old equipment manuals, access the Web and go to the ARRL Technical Information Service page at: http://www.arrl.org/tis/ and click on the TISfind link.
Figure 2—An antenna tuner installed between a transceiver and amplifier will provide a 1:1 SWR for the transceiver to prevent power foldback. However, the tuner does nothing for the SWR between the tuner and the amplifier.
From QST June 2000
