Youre not going to get a 375W carrier and DSB AM at 750W input. A SB-220 is
PS limited to around 250W carrier for a typical transmission length. I can
get the full 375W easily from my LK-500 with the external Power Pac. Even
more with SSB AM from the TS-950SD with a full 3300Hz of audio. Its also
possible to get a full 5-6KHz BW from that rig but I havent bothered.
Carl
KM1H
----- Original Message -----
From: "Bill Fuqua" <wlfuqu00@uky.edu>
To: "Carl" <km1h@jeremy.mv.com>; "ampS" <amps@contesting.com>
Sent: Tuesday, March 29, 2011 2:26 PM
Subject: Re: [Amps] Homebrew is back..
> 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@uky.edu>
>>To: "Carl" <km1h@jeremy.mv.com>; "amPS" <amps@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@telus.net>
>> >>To: <amps@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@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@rogerhalstead.com>
>> >> > To: <amps@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)
>> >> >>
>> >> >>
>> >> > _______________________________________________
>> >> > Amps mailing list
>> >> > Amps@contesting.com
>> >> > http://lists.contesting.com/mailman/listinfo/amps
>> >>
>> >>_______________________________________________
>> >>Amps mailing list
>> >>Amps@contesting.com
>> >>http://lists.contesting.com/mailman/listinfo/amps
>> >
>
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