Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

June 23, 2024, 10:55:13 PM

Login with username, password and session length

Recent Posts


Anybody build a hybrid tube/FET amp?

Started by Gewehr98, September 16, 2007, 08:50:29 PM

Previous topic - Next topic


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!

J M Fahey

Don´t waste your time. With 12 Volts nothing you do will beat a TDA2030 or similar. You´re not trying to build a real "Tube amp".


I would have to say on a 12v supply that a Tripath based map would be easily the best option. This is based purely on the fact that they are some of the nicest sounds amps out there at any price and when you factor in the low cost, and tube liek sound you have a real winner. I am current building a guitar amp based on one of www.41hz.com boards and if it is anything like as succesful as my hifi amps based on there kits it should be a huge success.


I've been toying with the idea of doing this. I'm a real novice with this stuff, though. Hoping to make something small, that could run from a set of batteries. I would like to try using a subminiature tube (like a 2P3 or 1S4 or 1S5) to drive an LM386. I've built the Li'l Gem and similar simple amps from the 386, but it would be nice to have a tube in there to see what it would sound like. I know the Gem uses a mosfet to drive the 386. A submini tube should be low-power enough to work in this application, shouldn't it?


OK, found my answer in a link posted on another topic in this forum. Ruby Tuby