[Amps] Ameritron AL-1200 problem -- More info..

[k8dio at windstream.net]

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