[Collins] 75S-1 Problem (update)

[pete wokoun, sr.]

Another source of audio crackle I've found in some of these older pieces is 
the ground connection on terminal strips starting to go bad.  Corrosion or 
what-not starts affecting the terminal strip to chassis junction.  Loosening 
the screws and re-tightening usually fixes it for awhile.  If you do it 
while the radio is powered up you'll immediately know when you 'find it'.  
Then, clean it up, not just retighten the screw.  Also, tube sockets that 
have ground lugs built into their mounting straps fall into the same 
category (on 51S1s, I think).  Naturally, take precautions when the things 
are powered up!

pete KH6GRT


>From: Dr.Gerald Johnson
>
>Audio crackle.
>1. Tubes.
>2. Leaky coupling capacitor between driver and audio output. Leads to
>damaged output tube.
>3. Way too much audio output power to high impedance load driving the
>plate voltage below the screen voltage frying screen of the output tube.
>4. Audio output tube plate bypass capacitor (HF roll off) breaking down 
>with
>excessive audio voltage.
>