[Amps] L7 FIXED (was L7 problems)

[Jim W7RY]

Glad you found it Paul!

And I put the new "D2" diode in the power supply because that is where the 
caps are.

73
Merry Christmas
Jim W7RY/0


-----Original Message----- 
From: Paul Kraemer
Sent: Sunday, December 11, 2016 11:08 AM
To: amps at contesting.com
Subject: [Amps] L7 FIXED (was L7 problems)

The L7 amplifier with the negative grid current on standby has been repaired 
and tested.
The problem was not the transformer I was suspecting but rather one of the 
0.05mfd disc ceramic filament bypass capacitors was leaky.  I don’t know how 
I missed it but after so many suggestions to check the feedthrough 
capacitors (like the L4B has but not the L7) I cut them loose and the 
problem went away.  The capacitors have been replaced and operation 
verified.

I also installed the recommended diodes across the meters and I installed a 
string of (8) 1N5408 diodes in the filament ct to the antenna relay contacts 
and placed a 100K 5W resistor across the contacts so the resistor is the 
cutoff mechanism in standby and shorted by the relay in transmit.  No more 
of the 120v going to the ct as Drake had it and now the amp runs a lot 
cooler with the small operating bias---you really have to be long winded on 
ssb to get the fan to kick into high now.

As far as 10m conversion here is what I encountered.  The amp already went 
to the extra position when I got it, there was not stop to remove or even 
any sign of one having been there.  I removed the 10m trap on the input and 
ran new input coax direct to the ts in the input compartment.  Not looking 
forward to what one would have to do to add or change the mica cap buried in 
the bottom of that compartment I cautiously tried the operation on 10m and 
found the match to my FT-950 as good or better than any band and the output 
was good.  With 50w drive, swr was very low, output was over 550w on 10m 
whereas it is approaching 650w on other bands.  I left it as is---it works.

Thanks to all for the advice and suggestions.  Got it repaired  and I couldn’t 
be happier with the outcome.

Paul K0UYA

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