This is an AM linear amplifier application.
Don't forget that the PEP value for 100% modulated carrier is 4x the
carrier level which is 200-250 watts.
So that translates to 800 to 1000 watts PEP.
73
Bill
At 12:34 AM 3/17/2010 -0400, you wrote:
>I would be somewhat concerned about the quality of an amplifier using
>the 833. Both the Matchlett and RCA data sheets show power outputs
>in the 200 - 250 W range per tube in "Class B telephony" service.
>
>I don't know if that is low level AM or if the efficiency falls off
>that much between class C (plate modulated or FM service).
>
>The 1980 Handbook does not give power output but indicates that
>efficiencies of "55 to 65% can be expected." The design was for
>1 KW input in class AB2.
>
>73,
>
> ... Joe, W4TV
>
>
>
>
>
> > -----Original Message-----
> > From: amps-bounces@contesting.com
> > [mailto:amps-bounces@contesting.com] On Behalf Of Roger
> > Sent: Tuesday, March 16, 2010 7:10 PM
> > To: Greg Weinfurtner
> > Cc: amps@contesting.com
> > Subject: Re: [Amps] Building 833 Amplifier. Hints and Suggestions?
> >
> >
> >
> >
> > Greg Weinfurtner wrote:
> > > Hi all,
> > > I am new to the list so be kind! I went through all of the
> > > threads
> > > on amps@contesting.com concerning an amplifier using 833's
> > and pretty much
> > > came up with very little usable information. Why 833's?
> > Why do I still
> > > deer hunt with a muzzle loader with just iron sites? Why do
> > people still
> > > build tube regens? Just 'cause I guess it is a challenge
> > and the 833 is a
> > > magnificent looking tube all aglow!
> > >
> > Others may not share my views but:
> >
> > I find the 833 intriguing but I've always thought it was
> > ugly<:-)) OTOH
> > I too have wanted to build up an amp using them.
> > w5jgv.com/downloads/RCA%20*833A*.pdf
> > shows a pair of them can run the legal limit and a single one can get
> > about 1200 PEP out, but this is with a plate dissipation of only 350
> > watts so a lot depends on the duty cycle. The filaments ae 10V @ 10A
> > thoriated tungsten so unlike many of the big power tubes the
> > filaments
> > are not terribly power hungry.
> >
> > With forced air cooling they are referring to 40 cfm out of a
> > 2" nozzle
> > directly over the tube with the flow directed between the
> > plate and grid
> > connections. Using a "swamped grid" approach takes about
> > 40-50 watts
> > of drive for a pair of them to get over the legal limit out.,
> > but that
> > can vary widely depending on plate voltage.
> >
> > I think a pair of those with the ability to view them while running
> > would be impressive.
> >
> > Due to the physical geometry I'd think (but don't know) that the
> > isolation of the input circuitry from the output would take a
> > bit more
> > care than with modern tubes.
> >
> > I've been looking at the idea of building up a similar amp
> > using a pair
> > of the GU81M Russian tubes. Those things are BIG!
> >
> > more below.
> > > I was an Electronic Design Specialist for Ohio
> > University for
> > > over
> > > 22+ years and have built a hybrid solid state 160 meter SSB/CW 100
> > > 22+ watt
> > > transceiver (Using a pair of 6146's) from the ground up, (
> > > http://oak.cats.ohiou.edu/~weinfurt/160mrindex.html
> > )including a 500 hz CW
> > > filter. Age is mid 50's and was in Tube/Solid State
> > transition during
> > > college years. Yep, slip sticks to calculators to SMD's.
> > BSS (Bachelor of
> > > Specialized Studies in Shortwave RF Engineering) is from
> > 1994, so that and
> > > being an EDS helped keep me in the loop until I recently retired.
> > >
> > > I have all the parts to put together 160 meter single band
> > > amplifier. I realize that it is a low mu tube of about 35,
> > and would
> > > probably not make a great grounded grid tube... but maybe
> > at 160 meters a
> > > pair of them could reach legal limit with less than 100 watts input?
> > >
> > > I have 5 each of 833A pulls, with only 6 months of
> > use. I got
> > > these from the engineer in charge and he said that usual
> > pull time is at
> > > least over a year or unless some failure occurs. But, the
> > owner of the
> > > station demanded that he do it every 6 months no matter
> > what the condition
> > > and he kept the 'like new' ones. Yes they are old, 20 years or so.
> > >
> > > I would prefer help from someone who has actually used the
> > > 833 in
> > > some type of RF circuit. But anyone with engineering
> > experience with a
> > > behemoth of this type knowledge would be great! I plan to
> > set up a web
> > > page and with my progress to keep those helping informed of
> > my advancement
> > > into the past!
> > >
> > > Characteristics for the 833A are
> > > at: http://oak.cats.ohiou.edu/~weinfurt/833A.pdf
> > >
> > >
> > **********************************************************************
> > > **************
> > > Plan.
> > >
> > > 1 Two of them in parallel or Push-Pull?
> > >
> > Single band you can take your pick. Use link coupling with
> > PP. Parallel
> > is a bit simpler.
> > > 2 Grid driven with a 55 ohm, 75 watt non-inductive resistor
> > to ground.
> > >
> > > 3 Pi output network or Pi L ? Or Link coupled output?
> > >
> > Single band, take your choice.
> > > 4 Operation is CW and occasionally SSB. Bias voltage on Cathode
> > > developed
> > > across about 60v Zener to ground?
> > >
> > According to the data sheet, you might want to run around -90
> > as a stand
> > by bias to limit dissipation.
> > > 5 Power supply is capable of 3000 VDC at 1 Amp.
> > >
> > That "to me" appears to be a bit toward the low end for these. But
> > running higher voltage gives a plate load impedance of over 10K ohms.
> > > 6 Forced air cooling up from pressurized bottom chassis to
> > box on top
> > > housing tubes and output components.
> > >
> > No. Due to the rather unique physical geometry of these tubes the
> > maximum cooling air is needed between the plate and grid
> > seals keeping
> > the temperature down to a max of 145C. 40 cfm from a 2"
> > nozzle directed
> > down and between the plate and grid terminals.
> > > 7 Tubes mounted in vertical position. Heat sinks for pin
> > connections.
> > >
> > That might be a tad unstable...BTW the only permissible mounting
> > position according to the data sheet is vertical.
> >
> > 73 and good luck,
> >
> > Roger (K8RI)
> > > Greg Weinfurtner AEE BSS
> > > NS8O
> > > 40192 State Route 689
> > > Meigs County
> > > Albany, Ohio 45710
> > > United States of America
> > > _______________________________________________
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> > >
> > >
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>
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