[AMPS] care to take a guess..? Alpha problem

Lamb k7fm@teleport.com
Tue, 29 May 2001 22:13:51 -0700

The fun begins.  Fixing something that does not work is the joy of ham

Perhaps the worst feeling when making repairs is taking something apart,
spending a lot of time confirming all the components are correct, then
finding something else was the problem.  So, here goes:

1.  The note did not say what element was in the Bird wattmeter.  Is it a
known good element?

2.  Is the dummy load a true 50 ohm load?  A dc resistance check is
generally ok to check with.

3.  Is there any resistance between the output connector and the plate
coupling cap?

4.  Since there has never been any known full output, do not assume that the
configuration is correct.  It may have come out of the factory with low
output.  I have seen an improper L network from a factory.

5.  Is the bandswitch on the right band?  Sounds stupid to ask that
question, but bad things happen if the knob gets moved to one higher band
and you drive the amp set for 20 meters with a 40 meter signal.  And,
consider what happens if the plate pi or pi-L network gets shifted one band
while leaving the input at the lower band.  Plenty of grid drive and plate
current, but low output.  I have seen that happen.

6.  What is the true plate voltage?

If the tube is driving ok, then the tube and the input are probably ok -
which means it is in the output circuit.   If the tube truly has that much
input, it will either be dissipating a lot of heat or something else will.

Or, perhaps it has a  parasitic suppressor added that is dissipating 1200
watts (ouch).

I once had a friend who purchased a new Rover 2000TC auto and had the water
temperature running in the red.  After a number of returns to the dealer, he
filed a lawsuit and the dealer took the car back and finally fixed it and my
friend was very happy.  It ran faithfully for 100,000 miles.  He finally
purchased a new car and gave the older car to his younger brother.  I was
visiting and he commented that the water temperature gauge has stopped
working.  I had some free time and volunteered to fix it.  I had been there
during the temperature fight years earlier and I had to smile as I found a
carbon resistor broken in two - in the temperature gauge circuit.  I pulled
it out and asked my friend what he wanted the temperature to read.  So, the
point is, if you do not find anything wrong you can simply recalibrate the
output wattmeter so that it reads 1500 watts instead of 200 watts.

73,  Colin  K7FM

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