• 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.

What can I do with these tubes?

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Hello all. I have bought a box of 40+ old tubes for $20 and am a tube newbie. I have electronics experience (build SS amps and design/build guitar pedals from scratch), but have not ever delved into the magical realm of tubes. I have intended to, and bought these to have something (anything) to play with.

I am hoping someone in the know can look at this list and tell me if any of them are good for anything. They all look mostly unused and appear to date from the 40s (from the codes I have looked up). The brands are mostly RCA and GE, with a few Sylvanias and Tung-Sols thrown in. Oh, and one unmarked TrueTone.

So, here is the list:

  • 25A7
  • 25L6
  • 3A3
  • 6AC7
  • 2x 6B8G
  • 6CJ3
  • 4x 6C5 (1 is GT/glass)
  • 2x 6H6 (1 is GT)
  • 3x 6J5
  • 2x 6J7
  • 6K6GT
  • 4x 6K7 (1 is GT)
  • 2x 6K8
  • 3x 6L7
  • 6SC7
  • 2x 6SJ7 (1 is GT)
  • 2x 6SK7 (1 is GT)
  • 6SN7GTB
  • 6SQ7
  • 2x GL-502-A
  • IP39

And also, I read TrueTone often did not mark their tubes. Is there any way to identify an unmarked one?

Thanks in advance for any help anyone can offer.
I was afraid it would be as DF96 suggested.

I am into guitar and was hoping to have something out of these to build an amp with. Or at least something I could build a working, although not usable, amp out of, even if it sounds horrible, just so I can see these things in action. Even if I used the wrong type of tube just to make a sound louder (and more crackly and distorted in a bad way). That way I don't care if I cook it.

So, the 6SN7 would be good for a preamp?

Oh, and two did get left of the list and they are, surprisingly enough, 6SL7GT's. Those could be used as drivers for an amp?

Is there a naming convention to identify which ones are diodes, triodes, pentodes, etc?

Also, is there an emergency room discount for electrocution while working with tubes?
DF96 offers sound advice, but I see a guitar amp there too.

Use the 6SN7 as the first and second stage and the 6K6GT as the driver. It would make a good first project. If you aren't into guitar, you could make a single ended mono hifi amp in much the same way.

Captn Dave said:
On second thought, you really need a 6SL7 for the guitar amp. The mono single ended amp is doable though.


I found this thread interesting because I had designed and built a low power stereo tube amp during my high school years in the 70's. I ended up using several 6SL7 along with PP 6K6, cathode biased, for outputs. The main reason was those valves and the power xfmr and output xfmrs were "in stock" for what ever reason in my shop class school lab. Saved some cash for sure in that project.

I still have that amp, it still works, and it even has a 5Y3 coke bottle rectifier.
I have always liked octal base valves. I think part of the reason back then
was because of the ease of wiring to the sockets instead of smaller sockets.

I do see a couple other valves in your list that "could" be utilized for audio projects like the 6J5 for one example. These are only a single triode and would not be as space saving as dual triodes, but fun nontheless.
I used some other valves in your list when I had built a (non FCC approved) AM broadcast band radio transmitter in my teen years. It actually worked, I still have it on a shelf in my lab at home.

Enough rambling here for me.

Carry on and enjoy
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