Monday, June 14, 2010

Carbon Plate?

Wow... You get new and crazy things every day from eBay. I buy a lot of the older small to medium sized transmitting tubes. I think they are genuine bargains lost in a world of high dollar 12AX7's. Most are directly heated triodes, my favorite style of tube. The real cost of using these babies is in the associated iron. Luckily, I know a guy who can wind that for me (wink!), so I keep buying all these strange old oddballs.

I have purchased quite a few of these 834's over the years. Some have fins. Make that some have one fin, some have two fins, some have three. Several different manufacturers made them. They aren't plentiful, but they also are not in demand. It is just a good old triode. I like 'em. I like 'em a lot. I guess I first fired one up in Class A1 about five years ago. Here is an old picture with a 15E driver.

Notice that the plate is a dull grey color. Definitely a metal plate. All of my tubes have been metal plates up to this point. I recall looking at the RCA Transmitting Tubes manual and thinking that the plate was drawn as carbon, but until a few days ago, I had never seen one.

See how the 800 is drawn as a metal plate? The 834 is clearly drawn as carbon. Very black. So now how the heck do I find a mate? Oh, I know. Just like all the others. I will wait ten more years on eBay.

I guess it would be mean to not show one lit up. So here you go:

[to all the well-wishers: Thank you for your concern and good thoughts. I am back up to full speed. It wasn't fun. I hadn't eaten for too many days and was running a crazy fever. But I am well again. I've been soldering and clip-leading like my old self for two or three days now. Woo hoo!]


  1. I love the asymmetrical construction of the carbon plate. Have you ever used UH50s?

  2. Thanks for the tube porn :) That is beautiful!

  3. Good catch! That asymmetry is amusing. How do you attach carbon to anything? ans: drill a hole through it an use a bolt and nut! As to UH50's, yeah, I have a bunch. I think they sound similar, family resemblance and all. The surrounding components make or break any of these transmitting tubes, IMHO. My issue with UH50's has been getting good ones. My success rate is like one in ten. It is on the list of ten hardest to land working tubes - WL468, gassy; Lewis 4e27, gassy; 304th/tl, one or more filaments dead....


    PS, would you guys sign your comments?

  4. Run those tungsten filaments a couple volts high for a day and the gas might go away. Hot tungsten has a gettering action.


  5. "Hot tungsten." Is there a better two-word phrase?

  6. well, the metal-plate tubes of this type are somewhat self-gettering when run hot. Tungsten (thoriated) filaments are more self-cleaning when run hot. That won't solve gassy issues.

    I have at least 4 or 6 NOS/NIB UH50s but haven't tried them yet. What sort of op point are you using for these and what sort of output tranny? (for A1 operation)

    I'd put WE 242A/C on the top 10 list of pain in the ass tubes to find good copies of. Those are the worst, as far as gassy, I have found. 866jr globes should go on the list too maybe. Seriously arc-prone.

    -Ed Sawyer

  7. can we get a circuit for the 15E tube?


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