There's always the "classic" RCA design, which is seminal to all passive designs. You'll need to add a buffering voltage follower if a stand alone project is what you have in mind.
No matter which design you settle on, a DC heater supply is a must.
Edit: fixed typo
No matter which design you settle on, a DC heater supply is a must.
Edit: fixed typo
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dsavitsk said:Is a 12ax7 close enough to use in this circuit, or is the 7025 essential?
With DC heating, 12AX7s are FINE. The 7025 is a 12AX7 with a spiral wound hum bucking heater. The current production Sovtek 12AX7LPS is a 7025 equivalent.
While you MIGHT be OK using AC heating on the 'LPS, why take the chance, when setting up a 7812 regulated heater supply is really easy.
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