First SE EL34 "triode" project: Help me understand dissipation?

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Hi all,
I'm working on a my first hi-fi amp project. I'm basing it on the schematic & description for the triode-strapped EL34 SE project at the Angela website. A schematic is here:
http://www.angela.com/catalog/how-to/SE.EL34.html (I'll put a hotlink below too)
The design as shown in the schematic has a plate voltage of 375, a cathode voltage of 28, and a cathode resistor of 880 ohms. I'm trying to ballpark the dissipation for the design as specified in the schematic, because something seems wrong with my own build (I currently have a plate voltage of 400, and a cathode voltage of only 15 volts with an 820 ohm cathode resistor).
Before I just start tinkering with cathode resistor values, I wanted to determine the dissipation in the specified design. But I don't know if I'm just doing the whole thing wrong (I've never tried to calculate dissipation for a pentode before, let alone for a triode-strapped pentode).
I know these formulas:
Plate Current = (Cathode Voltage/Cathode Resistor Value)-Screen Grid Current [I just ignore the Screen Grid Current here, right?]
Plate Dissipation = (Plate Voltage - Cathode Voltage) X Plate Current
When I use these equations, the number I'm getting - 11 watts for the design as specified in the schematic - already seems really low for an EL34. When I do it for my own build, I get about 7 watts - even lower.
First, am I doing the math right? If I am, should I drop the plate voltage to 375 and shoot for the same dissipation as the specified design? Or leave it at 400 volts? If so, what cathode current and/or dissipation should I shoot for?
Thanks for helping a newbie...

http://www.angela.com/catalog/how-to/SE.EL34.html (Open in New Window)

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Topic - First SE EL34 "triode" project: Help me understand dissipation? - Hugh 10:21:26 03/06/07 (2)

Re: First SE EL34 "triode" project: Help me understand dissipation? - Anthony Dockrill 16:40:42 03/06/07 (0)

Re: First SE EL34 "triode" project: Help me understand dissipation? - Chris O 10:45:23 03/06/07 (0)

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