One of my first linears I built as a high school kid back in 1960 used a
pair of 833A in push pull in and out. I had a bunch of big amp parts given
to me and that is what I built. The power supply was a pole pig with a pair
of 866 rectifiers. Of course, it also required a significant grid bias
supply.
Plug in coils with swinging links and split stator tuning capacitors. Not a
design for multi bands but nobody asked me to "say again" on 75m with that
amp.
I always wanted to try a more modern approach with one tube but I also
thought they were ugly and sold them.
Paul K0UYA
----- Original Message -----
From: "Roger" <sub1@rogerhalstead.com>
To: "Greg Weinfurtner" <weinfurt@ohio.edu>
Cc: <amps@contesting.com>
Sent: Tuesday, March 16, 2010 6:09 PM
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 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
>> _______________________________________________
>> 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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|