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[AMPS] Swan has Big Bang !!! ??????

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Subject: [AMPS] Swan has Big Bang !!! ??????
From: (KB7WW Art Moe)
Date: Fri, 06 Jul 2001 20:38:23 -0700

Well after 30+ years my Swan MK 6 finally died, WITH A BIG BANG !!

I thought I would run my repair plan by the group to make sure I don't 
miss anything. If you want to look at the schematic it's here.

The amplifier had been turned on for about an hour and used to make 1
qso about 45 minutes before it blew. KL7N0 a weak double hop E's
signal from Al in Fairbanks.

After first inspection the following damage can be seen visually.

In the power supply 4 of the equalizing resistors are charred and part
of each is burnt away. These are all in the same leg of the voltage
doubler.  Nothing found bad in the RF deck. The 4 amp fuse in the 
negative lead is not blown, one of the Primary fuses blown.

Plan of attack to repair the failure.

1. Check each of the capacitors in the HV supply. I will run each of them
   up to there working voltage through a resistor, and hold them at that 
   voltage for a while.  Is an hour long enough????  If they pass this test 
   should I run them above working voltage????????

2. Check the power transformer for shorts and voltage. Replace if needed,
   yes there available, but big bucks.

3. Replace the diodes (surely one or more are gone) Now what do you recommend,
   and where can one get them at a good price and no minimum order. I understand
   that modern diodes do NOT require resistor and capacitors TRUE???? The 
   original had 8 diodes in each leg should I use more????

Thanks for any help.


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