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

[TexasRF at aol.com]

LLoyd, I would suggest you use a different power meter on the output to  
verify the accuracy of your measurements. 
 
With 2500w+ input power and 300w output power, there is a loss of 2200W+. I  
would expect to see the tube or some other component in melt down if this was  
truly the case.
 
73,
Gerald K5GW
 
In a message dated 12/1/2008 6:15:26 A.M. Central Standard Time,  
k8dio at windstream.net writes:

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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