[Amps] Tank tweaking
Sun, 22 Sep 2002 11:15:28 -0400
Bill Coleman N2BC
----- Original Message -----
Sent: Sunday, September 22, 2002 10:42 AM
Subject: Re: [Amps] Tank tweaking
> >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. 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 - 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.
> >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.
> Search reveals no _Q_ or _q_ in message body. He who dance around Q can
> never achieve bliss...
> Bill K2AME
> Amps mailing list