[Amps] Building 833 Amplifier. Hints and Suggestions?

Roger sub1 at rogerhalstead.com
Wed Mar 17 00:20:25 PDT 2010



Joe Subich, W4TV wrote:
>   
>> 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.
>>     
>
> 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 data sheet is interesting in that is shows a wide range of output 
power from the 200-250 watts above to over 1200 watts. They show a 
maximum plate voltage of 3000 and turn around and put more than 4000 on 
the plate with a resulting PEP output of over 1600 watts for a pair of 
tubes.. It appears to be more than just the class of operation. IOW 
reading the sheet it appears if you can keep the tube cool within specs 
be it convection cooled or forced air cooled, (145 deg C on grid and 
plate seals)  the tube can do the job.  OTOH I have no idea as to what 
the IM products are at these various voltages and power.

Just like the Russian GU81M they appear to be capable of a lot more than 
you would expect.  A pair of the GU81Ms for  instance is listed at being 
capable of 3KW out in SSB, or CW with no forced air.  One user told me 
the only way  to hurt one would be to take a hammer to it.  I don't 
think the 833A is quite that versatile with only a 350 watt plate, but 
still...
> 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. 
>   
To me the data sheet would indicate a pair of them are certainly capable 
of the legal limit out if you don't exceed the seal temps or melt the 
plates.

73

Roger (K8RI)
> 73, 
>
>    ... Joe, W4TV 
>    
>
>
>
>
>   
>> -----Original Message-----
>> From: amps-bounces at contesting.com 
>> [mailto:amps-bounces at contesting.com] On Behalf Of Roger
>> Sent: Tuesday, March 16, 2010 7:10 PM
>> To: Greg Weinfurtner
>> Cc: amps at 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 at 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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>>> Amps at contesting.com 
>>>       
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>>     
>>>   
>>>       
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>>     
>
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>   


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