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EL802 driving a 845 ?

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Hello !

The latest silly idea of the day !

Driving a 845 with a single stage !

EL802, G2 = 170v, Ia = 20mA, Rk 90 Ohms un bypassed, RL = 12K, B+ = 500v.

Did WE already used a penthode to feed a 300B ?
Plate curves look like a tetrode, and I can't see any suppressor inside, just two beam plates !

Yves.
 

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I tried this with a similar tube (12GN7). The output voltage is enough but you need more current to overcome the miller effect of the 845. Think perveance. At the very least a 12B4 or 12BX7, a triode strapped 6AU5 works well. My 845 amp uses a 417A gain stage into a 6AH4 triode.
 
EL802 driving a 845?

Not so silly at all! But then you won't really know for yourself until you try it!

I'm presently using a single-stage 8077/7054 to drive an 845B. I run about 225V at ~20ma on the plate with a 25K load, directly taken from the 845's 730V plate supply, with 150V on the screens. Just like the old and venerable WE91, it has that technicolor midrange and very good frequency extension both up and down. I measure a -3dB point at the top of about 60kHz with MQ FS100 output trannies and get about 15W out at 5% thd. I've had no motivation to return to my 6A6/300B drive stage.

I've also tried a 6CL6/6677 and a 6197 and they work fine, too. They're also a bit more filament friendly, as the 8077 requires 13.5V. I haven't tried the 12GN7; generally speaking super-high-gm tubes aren't my cup of tea.

JL
 
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