Many years ago as a teenager I ran a pair of 250TH in grounded grid.
They worked fine but remember that then the legal limit was less than now and
measured quite differently, Plate input power.
The gain was low but when driven by my pair of 6146B tubes they
worked out just fine.
Had to add a bit of bias to the grid (-65 to-75 volts) but no problem there.
The reason I mentioned this is that the Amplification Factor and other
characteristics of
the 250TH are very similar to the 833. But it is more like one and a half
250th tubes.
73
Bill wa4lav
At 02:18 PM 3/16/2010 -0400, 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!
>
> 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?
>
>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?
>
>4 Operation is CW and occasionally SSB. Bias voltage on Cathode developed
>across about 60v Zener to ground?
>
>5 Power supply is capable of 3000 VDC at 1 Amp.
>
>6 Forced air cooling up from pressurized bottom chassis to box on top
>housing tubes and output components.
>
>7 Tubes mounted in vertical position. Heat sinks for pin connections.
>
>
>
>Greg Weinfurtner AEE BSS
>NS8O
>40192 State Route 689
>Meigs County
>Albany, Ohio 45710
>United States of America
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>Amps@contesting.com
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