My original posting to the group was in regards to a problem I have with the
Al-1200 on 160 mtrs. I have since borrowed a Cantenna dummy load so I could
check the amp on other bands. My driver is a TS-2000 going through an old
Kenwood antenna tuner. I am measuring 25 ma in CW and 125 ma in SSB positions
with no drive. My problem is that I am getting very low efficiency. Here are
some readings that I have taken:
Approximately 75 watts drive power
40 mtrs - CW position
Plate Volts = 3400 vdc
Ig = 200 ma
Ip = 750 ma
Power Output = 300 watts
Power Input = 2500 watts
160 mtrs - CW position
Plate Volts = 3400 vdc
Ig = 200 ma
Ip = 700 ma
Power Output 450 watts
Here are few things that I have tried from suggestions on the group:
I used my cap meter to check all of the padding caps. All of the doorknobs and
the small caps on the pc board checked okay.
I inspected the bandswitch contacts for signs of arcing.
I used a MFJ antenna bridge to check the ability of the amp to resonate. I put
a 2.7K resistor from plate to ground and fed the bridge into the coax line at
RFC 4. I calibrated the bridge with the Cantenna. All bands, except 80 and
160 meters gave me a deep null on the meter when I tuned the Plate and Load
controls.
I checked the 1N5408 diode on the capacitor board and that was okay.
The input swr is below 1.5:1 even without my tuner in line.
Can the tube be the problem??
Thanks,
73, Lloyd K8DIO
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