[Fourlanders] UHF contest, Amps, Sept contest

[Bob Lear]

I'm not operating in the UHF contest.  It has just been too hot to 
consider putting up antennas for it.  I will start taking stuff down for 
the September contest soon.

I have been working on my 6m amp for the past week, mostly drawing a 
correct schematic of the control board and control wiring which was not 
correct on the supplied schematics.  I still don't understand it, but 
I'm trying to figure it out.

Anyway, no joy in mudville.  The 6m amp still is doing the same thing. 
Full output indicated by meters:  normal Vp, normal Ip, normal Ig but NO 
output on the wattmeter.  NONE.  Doesn't move the needle at all and when 
bypassed, the drive will move the needle.  Still have a couple of more 
things to try next.  I have changed wattmeters and jumpers numerous 
times.  Both my 2500 watt slugs read properly when tested with the 2m amp.

As to Jim's 2m amp, it was a relatively simple fix.  The meter 
multiplier resistors had increased in value significantly (two were over 
2 Mohms!) and thus indicated a lower B+ voltage than actual.  I replaced 
the three 1 Mohm 5W carbon resistors with some 1 Mohm 5W units that I 
had gotten from Dick some time back.  I did not calibrate the B+ with an 
external meter, but the readings are reasonable now anyway.  Vp No load 
is 2850 dropping to 2500 under load of 550mA Ip, 25mA Ig giving 700W 
out.  I also got it to 800 out while testing with my FT920/DEMI 2m 
setup.  The loading capacitor that we fixed before is still working FB 
and no further indications of arcing.  It is ready for the contest now. 
  I did find that there were several errors in it's schematics also. 
Most were the same as the ones I found on the 6m control board as it is 
the same board, but what prompted me to start checking the actual 
circuits against the schematics was the fact that the meter multipliers 
weren't even shown on the 2m Commander schematic and they were shown on 
the wrong place on the 6m schematic.  I've sure learned a lot about 
these two amps.  I am drawing up corrected schematics for the manuals in 
addition to the copious notes I made on the originals.  I still don't 
understand how they work though as there are differences.  For example, 
the 2m amp shows a B- resistor on the schematic, but there is not one 
actually in the amplifier.  I don't know how it works this way, but it 
sure seems to work.  I haven't found another amp schematic in my 
investigation that is similar and doesn't use a B- resistor.  Any ideas 
from the peanut gallery?

Looking forward to Shelby and the September contest while trying to keep 
cool during this heat wave!

Bob