• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

some help for a newbie


I'm not new to electronic but i want to start using tube for electronic. i have recently found some old tube and would like to use them for practice.

They was taken(wekk suposed to be) from an old radio and it was working. I check the tube and they seem to be good.

I would like to know what would be an easy and cheap way to make those little guy work. Also some of them must be some sort of rf or maybe something else so I would like some info on them if someone got time to lose on that.

The tube number are:


the two others are unmarked.

tanx for any help.
Those tubes aren't generally used for audio.If you want to learn about tube electronics,a good approach is to either build something from a kit or look for a working piece of gear and get a schematic for it.This way you can study a working circuit,which is pretty helpful.Doesn't have to be anything fancy.Could be something like an old PA amp or whatever.As long as it works OK. The 2 pieces that started me going were a Fisher 400 receiver and a Harman Kardon integrated amp.This is the best way if money is an issue.Search the tag sales and second hand shops. Eventually,you'll find something.It's a lot easier learning from something that works.
The two output tubes tubes that I would recommend to the first time audio builder would be the 6AQ5 and 6BM8. The 6AQ5 will work in any circuit that features the 6V6, and they are so plentiful and cheap that you can experiment with (near) reckless abandon. I would highly recommend the 6BM8 for the first timer simply because of the circuits involving this tube require so few parts. In addition, there are literally hundreds of web pages (most of them in either Japanese or Korean, luckily schematics are schematics no matter where you're from) dedicated to using the 6BM8 in audio. You could build a stereo power amp with only two 6BM8s. Good luck and welcome to the world of tube DIY.
Hmmmm, given the tubes you're listing, the other two are probably a 35W4 and a 50C5. The 35W4 is a half wave rectifier tube and the 50C5 is a power amp pentode (beam tetrode?)

It's easy to tell the 35W4 and 50C5 apart by looking at their internal structures. The 35W4 plate will be smaller than the 50C5 and "hug" the cathode more closely.

If you are motivated enough, you could probably build a mono power amp with the 35W4, 50C5, and the 12AV6 (hope you saved the output transformer). You won't need a power transformer, but you will need to drop the line voltage to the heaters 22 volts (assuming you're using 120VAC line) so use the appropriate dropping resistor. You won't need the two diodes in the 12AV6; these were used for the detector and AVC in the radio and won't be needed in the amplifier. I'm attaching the schematic for a radio that uses these tubes so you can study the amplifier portion and perhaps hack the design to make your amp. Good luck.



  • aa5diaa.jpg
    59.5 KB · Views: 435


2001-06-01 4:53 pm
Dangerous circuit

You should not build an amplifier without using an isolating transformer of some kind. The schematic shown above is an example of the classic non-isolated radios that were built back in the days before transistors. This approach is fine for a radio or TV set that can be placed in an insulating box (wood or plastic), and does not need to connect to anything else. To connect to an external signal source you need to expose the internal "ground" as part of the signal input. There's a 50-50 chance this terminal could be the Hot side of the AC line and will electrocute somebody, probably you.
You can buy 120-to-120 volt isolating transformers for not too much money.
If it's guitar effects that you're interested in, check out: http://www.geofex.com/
Most of their tube schematics are for amps but I think I remember some for pre-amp stomp boxes using 12AX7's.

These sites have some good information on tube circuit design for newbie-types:

I'm starting my first tube project, too, but luckily there are lots of places on the web for info. DIYAudio is definitely one of the best for answers to questions.