I need some troubleshooting help on a basket-case Hammarlund Comet Pro that I'm trying to restore. Here's the schematic:
http://www.nostalgiaair.org/PagesByModel/994/M0008994.pdf Mine is the early model with the only gain control a pot that varies the voltage on the cathodes of the two 58 IF tubes. This one was a real mess when I got it but I love these old Comet Pros so I want to get it performing well.
Here are my symptoms: There is low distorted audio when the gain control is turned fully counter-clockwise. As I turn the control clockwise, the audio gets louder but gets very distorted. Right as it gets to full volume, the audio gets clear but is very, very loud. I can't get clear audio at a lower volume.
I have recapped the set (except for the 1 mfd cap right after the second detector). I disconnected the gain pot and tested it. It it turns from 0 ohms to the full 12K ohms. (I used a DMM so I'm not sure just how smooth the change in resistance is). The gain pot causes the cathode voltage on the IF tubes to vary between 0 and 13 V. All voltages in the set are in the ballpark. The resistors all test within 20% or so of spec.
Does anyone have any ideas?
As always, thanks for your help.
Joe Connor