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

[cemilton at aol.com]

GM Lloyd,

Curious..........why the tuner between the 2000 and the amp?

73
W4MIL
Chuck

-----Original Message-----
From: k8dio at windstream.net
To: amps at contesting.com
Sent: Mon, 1 Dec 2008 7:15 am
Subject: [Amps] Ameritron AL-1200 problem -- More info..










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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