[Amps] Homebrew is back..

Tue Mar 29 11:26:19 PDT 2011

    By the way. I do like old broadcast gear. But a beginner building from 
scratch on a budget can get legal power limit using a linear amplifier and
low level modulation in a very compact package. That would only be about 
750 or so watts plate input power. Not the classic way but should work well
within a budget.
    I used to have a old Phasatron 250 watt FM transmitter that
I sold a collector that really wanted it for a $1/lb. It had a pair of 
4-250As in the final.

73
Bill wa4lav


At 01:09 PM 3/29/2011 -0400, you wrote:
>Youre not going to get 100% modulation with "economy" approaches much less
>125% positive peaks and BC quality audio.
>
>The Gates frequency response is 30-12000 cps within 1.5dB.
>
>Carl
>KM1H
>
>
>----- Original Message -----
>From: "Bill Fuqua" <wlfuqu00 at uky.edu>
>To: "Carl" <km1h at jeremy.mv.com>; "amPS" <amps at contesting.com>
>Sent: Tuesday, March 29, 2011 12:11 PM
>Subject: Re: [Amps] Homebrew is back..
>
>
> >   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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> >>
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