On Sun, 14 Feb 1999 08:47:44 +0000 W7XU Arliss <w7xu@dtgnet.com> writes:
>
>Hi,
>
>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
>situation.
>
>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
>lid.
>
>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
optimized.
Is the plate choke or plate blocking cap eating up power?
73 Carl KM1H
.
For >
>Thanks & 73, Arliss W7XU
>
>
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>
>
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