[MIham] Blind Ham Needs Audio Repair Assistance

[Duane Fischer, W8DBF]

Hi All, 	

	I am in Glint, MI Genesee Township. I have a H. Scott LK-72b stereo amplifier.
It was just recapped and completely gone through by a friend in CA. He burned
her in for four or five days with no problems.	
	
It was very well packed, padded and cushioned when UPS made the transit. No
problems there. All of the tubes were shipped in a separate box.	
	
Everything appeared fine. I plugged the four 7591a into the proper sockets being
certain to match the correct tube to the correct socket. The bias was already
sset. I plugged the rectifier tube in. I checked all other tubes to be sure they
were properly seated. Everything was as it should be. 	
	
I plugged the H. Scott LT-110 FM tuner into the unswitched power outlet on the
back of the amplifier. I did not turn the tuner on! I connected the speakers,
being certain that the jumpers were set for 8 ohms. Speaker polarity was
correct.	
	
I connected the FM tuner output to the FM tuner input on the amplifier input
side. I connected an antenna to the FM tuner. 	
	
I then plugged the amplifier into the wall outlet. I turned it on.	
	
I heard a soft hum immediately from the right rear of the chassis. The amplifier
and tuner have no cases, by the way. The big power transformer is located here.
This hum was NOT from the speakers, some six feet away. It was immediate, no
warmup time involved. 	
	
About two seconds after I turned the amplifier on, I heard a sharp pop, heard a
sizzling sound and instantly shut the power off. (I still had my left hand on
the on/off switch). I was bent over the amplifier.  I smelled burne components
at this time. 	
	
I immediately disconnected the line cord, unplugged the tuner, unplugged the
tuner input cable from the amplifier and disconnected the speakers. Although I
smelled no smoke at this time, I still carried it outside and set it on the
concrete sidewalk just in case.  	
	
The fuse did not blow. 	
	
The only visible damage was a large resistor to the right of the rectifier tube.
The side was blown right out of it. 	
	
As far as I know, there was insufficient time for B+ to be present, as the
rectifier tube had not even warmed up. This blew in no more than two seconds
after power was turned on. 	
	
I need somebody in MI with experience who is willing to examine the amplifier,
determine the problem and repair it. I have the service manual and schematic.	
	
If you are willing and able, please contact me by e-mail. Thanks! 	
	
Duane Fischer, W8DBF	
dfischer@usol.com