[Boatanchors] Squeal

[Alex [Temple Boatanchors]]

At 02:23 PM 7/6/2018, you wrote:
>Heath SB101.  When I turn audio gain up over one quarter of range, 
>radio takes off into a loud squeal.  RF gain or mode settings make 
>no difference.  Suggestions?  Bad PCB ground maybe?

Maybe a microphonic audio tube? Turn down the volume under a quarter 
of range and gently tap on the audio tubes one at a time (might as 
well do it to all of them) and see if you can hear a thumping noise 
in the speaker. That would indicate the tube is sensitive to 
vibration, so when the audio is turned up the sound will make the 
tube vibrate and cause feedback, just as it was an open microphone. 
Hope that helps.

Alex