>A few months ago I posted a query about crummy efficiency on my homebrew
>5CX1500 AB1 amp. I have cured most of the original problems by re-doing
>the input circuit and tweaking the output tank coils. Oh, 'tweaking' means
>creating a lot of scrap copper.
>
>It works well on 10 through 80. Efficiency on the order of 60%, the
>'real world' tune and load pF are very close to the calculated values.
>I'm using a spreadsheet I cooked up from the W5FD formulas.
>
>But... I have been chasing my tail on 160M. The calculated C1 / L / C2
>values at 1.9 MHz are 298pF / 25.47 uH / 1708 pF.
** What is the RL and the Q ?
tnx
>Actual values are 276
>pF / 25.53 uH / 600 pF. Efficiency is off to 48%.
>
>The tank coils are 3/16" copper tubing for 10/15/20 and a hunk of coil
>stock for 40/80/160. Plate blocking may be a bit small @ 800 pF
** 800pF is not small for 160m because the Z is not low.
>- would that have such a huge effect on loading? The plate choke is an
RFParts
>RFC-3 (Ameritron) 225 uH & I don't feel any undo heating. Plate bypass is
>a pair of 500 pF @ 30KV caps & I've tried adding an additional 1000 pF 6KV
>disk ceramic with no effect.
** 1000pF at 1.8MHz (88-ohms) is not enough to keep RF out of the PS.
>
>The input is across a 200 ohm grid resistor with a 4:1 balun. It is
>untuned on 160 and 80, tuned on 10 thru 40.
>
** Sounds good.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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