[Amps] Basic Question Finding Passive Component Up in Smoke

john starr001 jstarr001 at hotmail.com
Tue Apr 9 23:41:32 EDT 2013


I am a beginner learning amplifier basics and decided to build a simple 6146 class C final CW rig with a 6CL6 driven crystal oscillator much like the Eico 720 or Globe Scout.  The power supply is a full bridge 600v B+ and 300v non-regulated screen supply.  I did something stupid and accidentally grounded the B+ supply.  So I blew the 3A AC line fuse but just before one of the components in the 6CL6 or 6146 circuitry went up in a cloud of smoke. I have visualized every cap, resistor and inductor and find no damage.  I have measured every resistor, directly or indirectly, in-circuit and all are to spec.  No open inductors and no shorted ceramic caps (all in -circuit).  I tested the power supply disconnected from the RF circuit and the supply, without load seems fine.  The 6146 and 6CL6 test fine as well.  I want to put it all back together again and test the voltages with the 6146 and 6CL6 removed but I am a chicken worrying about blowing up something else (like my transfomer the next time).   There was a obvious puff of smoke so something was lost.  I figure approaching this kind of problem must be routine for you guys working on amps so would appreciate learning what would be your next steps to find the bad part while minimizing further damage.  I thought the 6146 screen would burn up if the plate B+ were suddenly lost but it tests fine on my Hickock. tnx and 73john 		 	   		  


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