On Sun, 14 Feb 1999 08:47:44 +0000 W7XU Arliss <firstname.lastname@example.org> 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
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
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
>Thanks & 73, Arliss W7XU
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