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Topics - Gewehr98

#1
Tubes and Hybrids / Anybody build a hybrid tube/FET amp?
September 16, 2007, 08:50:29 PM
I've just started building a miniature tube amp, using the low-voltage 12K5 and 12U7 space-charge tubes.  I want to build what's essentially an iPod amp, using a 12v, 5 amp LCD monitor/laptop power supply, and drive a pair of bookshelf speakers to around the 5-watt level. (ala' a nice combination of new vs. old in a very small package) I want tubes because I use the same in my guitar amps, as well as my Jolida 502A main amplifier for my living room system. 

However, the 12K5 isn't a real powerhouse of a tube, so I'd like to add a FET or some other solid-state output stage to the tail end of the 12K5 while still keeping things in the 12 volt power supply range.  The LM386 is often used ala' the Ruby Tuby, but is still somewhat shy on the output power.   I notice through my MCM Electronics catalog that there are several nice audio amplifier ICs out there to select, but I wanted to tap the minds here to see what kind of trouble I'm in for.

Also, if I'm remembering things correctly, the plate output of the 12K5 likes to see some sort of load, so running it directly into an IC or final output transistor requires some intermediate resistance, right?  Would this be a good place to add a volume potentiometer, or should that go somewhere else in the circuit?

Thanks in advance for any suggestions and help!