[TenTec] Argo #505 VFO Issues

[Byron Tatum]

Hello-
  I went through a really nice Argo #505 that I bought years back. I wanted to replace all of the electrolytics on the PC boards and give it a general check-up. The radio really works well but one issue that it had, from the day I bought it, was the PTO was very non-linear in the top 10%-15% KHz of the tuning range, on all bands. The amount it was off was around 20 KHz at top end of 80 meters (when zeroed at lower end); most of this non-linearity was in the top 75 KHz or so. 
  Since it was this way on all bands I looked at the PTO itself rather than start trying to re-span the tuning range with the pairs of coil slugs.
  When examining the PTO mechanism the non-linearity was occurring on the end of the tuning range where the core was most-withdrawn from the coil. 
  Sure enough, the coil form had loosened from the 2 plastic holders and moved toward the rear of mechanism, an estimate is slightly less than 1/8". There was some of the coil form protruding beyond the backside of rear plastic holder; I pushed on it with the tip of a small screwdriver until the rear edge of coil form was flush with the rear edge of the black plastic holder-I could tell by the appearance of the portion of coil form that moved out of the mounting hole (of black plastic holder front edge) that I had the form the way it originally was. I temporarily powered up the radio and made a quick check of the dial tracking (had to adjust on cores some) but saw real quick this was the fix so I glued the PTO form in place with a small amount of cement.
  After re-adjusting the cores some the PTO linearity is about as good as can be had with these sets; zeroed at bottom edge of band it was off about max 3 to 5 KHz max anywhere else in said band 80-15 meters.
  By the way, I cannot find any info on the correct way to tune the pairs of PTO tracking coil slugs. I have been using the bottom core to adjust for zero beat at "zero" on tuning dial and the top core to adjust the span (zero beat at "500" on tuning dial). Anybody know if this is how Ten-Tec did it?
                    Thanks, Byron WA5THJ