Tube DIY Asylum

Thanks for the link, but...

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In Reply to: Re: Why do I have DC on my cathode-biased input tube's grid? posted by mikeyb on April 27, 2007 at 11:03:35:

This is a paralleled triode, so having a 120K plate resistor and 680 cathode resistor amounts to 60K plate load and 1360 ohm Rk's.
So looking at the datasheet you posted, closest design is Vp 200, Rp 47K, Rk 1K5. Whopping 8.5% distortion! Yikes!
So I had .4 volts on the tied cathodes, which works out to .58 ma, or .29 ma per triode, which is about a third of the .89 listed on the datasheet. Is this another indication of a bad tube?
...fwiw, a priest told me the tube tested good, yes, a priest, who sells tubes on ebay in his spare time... hmm, maybe I will try another when I get home tonight!

Follow Ups:

Hmm actually... - Alexo 11:39:22 04/27/07 (2)
Isn't having a 120K Rp ion a parallel triode like having 240K on each one? I've been thinking about that backwards... no wonder it's biasing so cold!
- Actually, actually... - Alexo 11:42:52 04/27/07 (1)
  Looking further down the datasheet, if you use a 220K Rp at 200 Volts, you need a 3.3K Rk, and bias to .36ma, so I am actually right on target for an "appropriate" bias.
  - And put in a 200K Grid Leak Resistor (nt) - Chris O 13:02:57 04/27/07 (0)
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