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
>>
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