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[AMPS] 6m amp

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Subject: [AMPS] 6m amp
From: (
Date: Sun, 14 Feb 1999 14:01:42 -0500

On Sun, 14 Feb 1999 08:47:44 +0000 W7XU Arliss <> writes:
>I think the efficiency of my homebrew 6m 8877 amp is 
>lower than it should be (currently about 50 %), and am
>looking for some suggestions on how to improve the
>The amp runs about 2800 V key down at 1 amp, with 50 mA
>of grid current, into a 50 ohm load.  Idling current 
>(set with a 12V Zener) is about 75 mA.  The plate 
>circuit is a Pi-L network patterned after Lauren Libby's
>(W0LD) HR article from July 1986, using a vacuum variable
>tuning capacitor, 3/16" copper tubing for the coil, and
>a 250 pF air variable for the loading coil.
>I've tried varying the coil size somewhat but that hasn't
>made any difference.  I also tried increasing the plate
>voltage to 3500 V, which reduced the drive requirement, 
>but didn't make a significant difference in the amp's
>efficiency.  The coil is about 1.5" away from the cabinet
>Other suggestions?

What is the drive power? What is the input circuit and VSWR? The input
network should be right at the socket and not thru a length of coax.

How good is the tube? Compare it with a known full emission one on 10 or
6M. Radio Recyclers is selling full emission pulls for $190 which is a
great price.

Try a straight Pi for comparison. That L coil can be tricky to get right
especially with close spacing to cabinet walls and lids. I prefer to let
a good LP filter do the clean-up work and a Pi is simple to get

Is the plate choke or plate blocking cap eating up power?

73  Carl  KM1H


For >
>Thanks & 73,  Arliss  W7XU
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