[AMRadio] DX100B oscillation problem

[JAMES HANLON]

If you suspect that your oscillation problem may be coming from the audio/modulator chain, just pull out the 1625 modulator tubes and see if that stops it.
 
I like to use an oscilloscope to go chasing an audio oscillation.  But if you don't have a scope, just use a pair of headphones with a capacitor in series, something around .05 mfd with a high volage rating equal to or above the highest B+ level you anticipate encountering.  Ground one side of the phones and touch the open lead of the capacitor to the tube grid or plate you are interested in, and you will be able to hear what the audio sounds like at that point.  If there is an oscillation passing through that point you will hear it.  One caution, there will be a substantial "click" when you touch the capacitor lead to a different B+ level or when you touch the cap lead to ground after the cap has been charged.  So shift the phones off your ears when you first probe a new spot.  
 
Jim, W8KGI