[Hammarlund] HQ-150 Problem

[Bill Stewart]

My HQ-150 has been working just fine until recently.  Now, on any cw/ssb sig (weak or strong), everything is fine until I adjust the sensitivity control upward into the 8-10 region. In that area, the cw tone freq. changes (probably around a kc) and wobbles a bit (I can use the sens. pot as a fine tuning control). I only get the freq change when I rotate the sensitivity pot into that area. Below that point, I can change the sens. pot with no problem. If I need to, I can adjust the BS and get the freq back to my desired listening tone and it will stay there...until I adj. the sens. pot again. A week or so before this happened there was some freq. jumping going on. I don't think the freq of the rcvr is changing, just something to do with the bfo tone freq. I see the wiper of the sens. pot (R39) feeds the cathodes of the 6BA6s (V2, V4). I changed the 6BA6s but ND. When I get a clear spot on the bench, I'll do some voltage checks around the 6BA6s. 

In the mean time, I'm just trying to get an idea before I lug the thing into the house. Has anybody run into this problem or got an idea about a fix. 

Thanks, Bill K4JYS