[Novice-Rigs] YTuned / Not-Tuned Input---Final PA

[Ed Swynar]

Good Afternoon Brian,

Thanks for the directions to your 2E26 rig website...

Wow! You've got a LOT of real estate to play around in with that set-up of
yours! I think that was my main problem, i.e. the darn thing was TOO compact
for its (and my!) own good...I simply out-smarted myself, I guess, with
probably all sorts of feedback paths that simply were unavoidale, resulting
in the unstable final...

BTW, did I tell you that prior to going to an untuned input, I did manage to
"dip" the feedthrough power with a neutralizing capacitor...? Alas & alack,
stable operation was simply not meant to be, because the rascal would
take-off on me just when I thought it was licked. That rig had a mind of its
own, I swear...

It's pretty tame now, though---and just in time for the QRN "season" on
80-meters, too (See...? That rig STILL manages to get the last laugh!)...

~73!~ Eddy VE3CUI - VE3XZ



----- Original Message -----
From: "Brian Carling" <bcarling at cfl.rr.com>
To: "Welcome to the Novice Rigs List!" <novice-rigs at mailman.qth.net>; "MOPA
GROUP" <MOPAGROUP at yahoogroups.com>
Sent: Sunday, May 01, 2005 1:20 PM
Subject: Re: [Novice-Rigs] YTuned / Not-Tuned Input---Final PA


> Guys - as Eddy has discovered there is nothing quite like a MOPA
> transmitter!
>
> I used almost the same configuration with mine. In my case it is a 6CL6
> driving the 2E26 final.
> As stated here I use just the RFC and then capacitive coupling from the
> plate of the osc to the grid of
> the 2E26...
>
> Try it - you will like it fine! See:
> http://www.af4k.com/2e26.htm
>
>
> Ed Swynar wrote:
>
> >Hi Gang,
> >
> >Anyone who has ever built a MOPA rig for the low bands, & then found that
the final RF amplifier stage is more T.P.T.G. oscillator than amplifier---as
I discovered to my chagrin with my 6AG7 driver / 2E26 RF amplifier---pull
the L/C network right out of the grid stage of the final, & go it alone with
the 2.5 mh RF choke in the plate lead of the driver...
> >
> >Your input will be untuned by doing this, but on the low bands you should
have more than enough drive, dependent upon tubes used. I'd be hesitant
about trying this on, say, 10- or 15-meters, but it seems to work well
enough for me on 160-, 80-, and 40-meters. Just watch for "double-dipping"
when tuning the final tank---if your VFO output is untuned, you may well be
peaking on a harmonically-related band!
> >
> >A lesson learned: when building that first-time GB rig, always remember
that LESS IS MORE. I started out with an ultra compact set-up here, using a
6DT6 buffer between the outboard 12AU7A VFO & 6AG7 driver, regulated voltage
on the 6DT6, selectable cathode / grid block keying, tuned drive, etc. etc.
What a mistake! I needlessly complicated things with such circuit
sophistication, & the thing never worked 100%...now I've pulled the 6DT6, VR
tube, made it cathode keying only, & extracted the L/C after the
driver---and the result...? It now works like it's supposed to!
> >
> >...AND I have a couple of less controls to fiddle with, & more room under
the chassis, to boot.
> >
> >~73!~ Eddy VE3CUI - VE3XZ
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> >
> >
> >
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