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Old 5th August 2004, 01:36 AM   #1
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Default 833a plate resistance ?

I have found a lot of pages with specks for this tube but none of them has the plate resistance.

Any ideas?

thanks,

Woody
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Old 5th August 2004, 02:41 AM   #2
GaryW is offline GaryW  United States
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The Amperex spec sheet at Franks Tube page 833a list 2375 ohms with 3000v supply and 50ma idle current, Class B. Pretty healthy voltage - more than I'd care to try to make safe.

These guys have done a lot of 833a stuff and supply to the hobbyist. Lancroft Audio. Looks like their site is being revised though.
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Old 5th August 2004, 04:56 AM   #3
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Default 833A Making plasma

I haven't yet used the 833A for an audio amp but have as a high powered, self excited RF power oscillator. This triode can process a lot of power! Here is one with a nice orange spot on the plate making a 22" hot fiery RF plasma discharge. Modulate this oscillator with a 500 watt plate modulator amplifier and you'd have a wide range plasma speaker!

BTW, if you DO get an 833A operating in an amp do not operate it with this bright a plate glow or it will not last. I was pushing this one hard for a very short test. A bit hotter and I could have melted a hole in the plate. The 833A shown has a tantalum plate. There is a graphite plate version called an 833C which can handle this kind of abuse and the plate will stay dark or just barely glow. A standard 833A will be more than plenty for any audiophile application.

Note that these tubes operate at lethal voltages and special knowledge and precautions are necessary to prevent from being killed. You do not get a second chance to have a mishap with this kind of equipment.
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Old 5th August 2004, 04:59 AM   #4
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Here is a much better photo of the actual plasma discharge I showed in the previous post. The space from the tungsten discharge electrode on top of the coil to the aluminum grounded target is 22". This may be of some inspirational value to those who want to pursue plasma speakers.
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Old 5th August 2004, 05:10 AM   #5
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Default plate resistance

Hello Woody,

my 833 amp was finished some a half year ago. I had the same "problem" when looking for the plate resistance. Here's a list of trial-and-error by me and other 833-builders:

voltage/plate resistance/current:
3 kV / 20K / 100 mA
2 kV / 10K / 150 mA
1,5 kV / 8K / 200 mA
1 kV / 5K / 250 mA
650 V / 2K / 290 mA

All the data in the tube handbooks are for Class B, push pull, 2 tubes, etc. Not for a SE amp (which i assume you're wanting to build ?)
I stuck with the 1000 V / 5 K option. And it works great.
My amp: input transformer - 6SN7 - interstage - 300B - interstage - 833 - output transformer. The attached picture is only the amp; the power supply is another chassis of the same size.

Lots of luck with your project. The 833 is worth it; great sound !

With regards,
Reinout
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Old 5th August 2004, 05:36 AM   #6
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Reinout,

You must have no pets or other forms of children around as that exposed plate terminal looks like an invitaion to disaster.

That is a large chassis. Nice job!

Are you plate loading the 300B driver or cathode coupling through the driver transformer?
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Old 5th August 2004, 12:14 PM   #7
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Default 833 chassis

Hi RCA-Victim,

your richt: no pets or children. But if they come (visitors) i'll place a cage over the amps. They are made for that purpose. Not very beautifull, put effective enough.

I like it without the cages....don't hide those tubes please. they deserve it to be shown.

In total the amp consists of 4 chassis: amplifier left/right with dedicated powersupplies.
280 kg.....so pretty theftproof.

Your question plateloading or cathode-coupling: plate through interstage coupled to the 833. The interstage is a step-DOWN interstage !

I saw you nice pictures of the arcs......mighty impressive !

with regards,
Reinout
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Old 5th August 2004, 12:21 PM   #8
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Default power supply detail

Ha RCA-victim,

the powersupply of my 833-amp is again the same size chassis (52 cm x 75 cm) and is stuffed with a lot of transformers and coils. There are 10 visible transformers/coils visible on the outside. On the inside are there 5 more.
The powersupply weigs in at 77 kg, whereas the amp does only weigh 62 kg.

Allmost all tubes have their own dedicated transformer / capacitor / coil powersupply line. In all a very stable power supply.

I can switch between 1000 - 1200 - 1400 VDC on the 833, but found no need for 1000 V+. The bias of the 300B is directly visible (panel meter) and can be adjusted while playing.

With regards,

Reinout
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Old 5th August 2004, 03:06 PM   #9
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Thanks for the help. I was sort of hoping to use it in inverting
mode but the new (plate) resistance would still be too high.

Woody
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