[Amps] Homebrew is back..

Tue Mar 29 09:11:28 PDT 2011

   Also, look at the tensioning springs on top and
see if they are  slightly and equally compressed.
If one filament strand breaks one or both will pop
up. Sometimes the filament will not drop out.
    I have not seen $5 or $10 new ones for a while.
But on the other hand, I have plenty and have not
been looking very hard.
     Good modulation transformers are hard to come by
these days. And if you really want linearity you need
a modulation choke. Many old AM broadcast transmitters
are built with these features and if you have one that
is great. I have one but sold the modulation iron to
a friend trying to get a AM station's transmitter back on
the air. The station's owner was really tight.
     But, since the legal limit is 1500 Watts PEP output,
you could get better fidelity, especially low frequencies using
low level modulation, maybe even screen grid modulation, and
a good amplifier. Not as quite as efficient as a plate modulated
class C amplifier but more practical sometimes. Face it, the modulator, which
is has to provide an output power of half the plate input power of the 
class C amplifier
on the peaks is class AB usually. The same efficiency as your linear 
amplifier and
has two more high power filaments to power. The overall efficiency is not a 
lot
better than a linear amplifier.
    I will have to say however, plate modulated AM transmitters are still 
cool from
an old timers point of view.
73
Bill wa4lav

At 09:19 AM 3/29/2011 -0400, you wrote:
>----- Original Message -----
>From: "Jim Thomson" <jim.thom at telus.net>
>To: <amps at contesting.com>
>Sent: Tuesday, March 29, 2011 7:17 AM
>Subject: [Amps] Homebrew is back..
>
>
> > Date: Mon, 28 Mar 2011 14:38:12 -0500
> > From: "Diane & Edward Swynar" <deswynar at xplornet.ca>
> > Subject: Re: [Amps] Homebrew  is back..
> >
> > Hi Roger et al,
> >
> > I use a pair of 813s in parallel grounded-grid service here in my
> > homebrewed
> > KW amplifier, and---I'm blushing as I type this!---but I have NEVER EVER
> > purchased any of the jugs that are in it, or the spares that I have here,
> > brand new...
> >
> > They are all either Hamfest finds, or freebies from friends.
> >
> > Life's far too short to pay-off a retiree's ransom for new & exotic
> > tubes---and I have yet to hear anyone at the DX end of my QSOs asking me
> > (or
> > expressing any care whatsoever) which tube(s) I might be using! Hi Hi
> >
> > ~73~ de Eddy VE3CUI - VE3XZ
> >
> > &&&  813`s  are a half decent tube....but not in the same league as a
> > YC-156, YU-148
> > or 3CX-3000A7    A single YC-156 = 14 x 813`s    A YU-148 = 20 x
> > 813`s.....and yes,
> > the the DX station will hear the difference.   The IMD  on the 813 and
> > 4-1000  is nothing to write home
> > about...and ditto with russian tetrodes.
>
>
>The 813 is in the mid -30's in GG, which is better than many xcvrs and
>certainly acceptable. Same with a 4X1 if run sanely.
>
>The 813 is still a hamfest $5-10 out of the carton. Just pass on ones with
>filament pieces rolling around inside and discolored glass. Many Ive picked
>up that way that look new but just a bit scratched from loose storage work
>as new at RF.
>
>With 4 in parallel use a vacuum variable, the 5KV 365pf that are so common
>are fine, or tap the 10M coil in the center with the Tune cap which gives a
>4X stepup for the required C. Do not add a seperate L coil.
>
>The last 4x 813 amp I built used the vacuum variable with the tap and it ran
>full power even at the high end of 10M.  Keep the layout compact, and with
>minimum length copper strap leads. A rats nest of wire wont cut it at 10M.
>
>Carl
>KM1H
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>  The folks with the infamous 4CX-1600B  in their Ten tec`s are
> > really screwed. Apparently, it can be converted to another tetrode. IMO,
> > I`d  convert it to a
> > chinese 8877....and be done with it.
> >
> > Jim  VE7RF
> >
> >
> >
> > **********************************************
> >
> > ----- Original Message -----
> > From: "Roger (sub1)" <sub1 at rogerhalstead.com>
> > To: <amps at contesting.com>
> > Sent: Monday, March 28, 2011 1:11 PM
> > Subject: Re: [Amps] Homebrew is back..
> >
> >
> >> On 3/28/2011 12:02 PM, Lou Spradling wrote:
> >> > It has been several years since I have attempted to "build something",;
> > and in
> >> > that frame I become an (operator). A real pleasure to pursue the hobby
> > with
> >> > researching material for 10-160 linear amps ! and in doing so I
> > discovered this
> >> > reflector !! Wow, a real goldmine of experienced builders in my
> > library'.  It's
> >> > great.
> >> >
> >> > Now, my problem is trying to locate one or more Tubes 4CX1600b for a
> > Ten-Tec
> >> > Titan II, OR. any thoughts or suggestions as how I should approach this
> > item. It
> >> > is working fine but it looks like a little rework of the final area
> > will be
> >> > required if I can locate a tube that I should use.?
> >>
> >> There are people on here who know a lot more about tubes than I, but:
> >>
> >> Unfortunately even though "The Handbook" still shows projects using it,
> >> the only 4CX1600B's left are the ones "a few" might have on their shelf
> >> for spares, or "that planned project". IOW they are no longer in
> > production.
> >>
> >> If you still desire a tetrode of that size or close to it, there are the
> >> 4CX1500Bs, 4CX1000s, Chinese FU728Fs in production.  There are lots of
> >> surplus NOS Russian Triodes and Tetrodes available with plate
> >> dissipation ratings from around 800 watts to 4000. but the price on the
> >> good ones is going up, but still cheaper than new 8877s or 4CX1600Bs
> >> when they were available.  Calling them good will probably raise Carl's
> >> blood pressure <:-))
> >>
> >> The field for legal limit triodes,  if you want a tube still in
> >> production.  8877s, 3CX and 3CPX800s as a pair, are popular, but pricey
> >> and available as tested pulls much more economically.  Although no
> >> longer made the 3CX1000A7s are still found occasionally.
> >>
> >> The more popular tubes on here are the substantially larger 3CX3000A7
> >> and 4CX3000A7 (ungodly pricey socket but available used) and the YC156
> >> (tube with handles and no socket required) is probably the most popular.
> >> Any of these can easily be set up to run the legal limit plus a bit, but
> >> we are talking tubes that weight from around 6# to nearly 10# and about
> >> 10" tall with about 5" diameters.
> >>
> >> 73
> >>
> >> Roger (K8RI)
> >>
> >>
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