Teonex 12AU7 Tube

Mykale · 622

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Offline Mykale

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on: April 08, 2022, 04:05:42 PM
Hello,

Looking for some advice. I bought 3 bottlehead cracks for myself and some friends. I built the first one and it came out fine. On the second one, there is noticeable left side hum from the bottlehead crack on the same setup that was fine for the 1st crack.
After reflowing all the solder joints, the problem didn't get fixed.

I noticed the 12AU7 tubes are different. On the 1st crack, it has a green label that is peeling off: "CONN USA 381226". The 2nd crack has a Teonex 12AU7. I noticed that there is a tube flash on startup, but googling around it seems to be normal for this brand.

I swapped the tubes and the 2nd crack sounded fine with no noise and the 1st crack has the noise now, so it seems to be the tube that's the problem.

For reference, the Teonex tube came with the bottlehead crack and was not purchased elsewhere.


Offline Mucker

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Reply #1 on: April 08, 2022, 07:20:34 PM
With a new Crack, I personally would let the tubes "cook" in the amp for a few hours (or more, 24-48) and retry a listen. Some tubes that have not been used for many years take some time to quiet down. If the hum didn't go away in a couple days or so, it could be the tube is just not a good tube.

I just received an old Sylvania black plate 12AU7 that had a huge buzz at first start, one of the loudest ones I've ever heard. I thought it was defective until cooking it over the course of the day. 8 hours later it settled down with just a tiny bit of white noise and sounded really good. I was ready to toss it but glad I did not.

It sounds like the amps are performing well otherwise. If they are quiet, you did a great job!

Edit: Another suggestion would be to clean the pins. I had a 2399 tube that was giving me some hum (from vibration I believe) and I went to town on the pins. I used high grit sandpaper on each pin and then coated the pins with deoxit. The hum was eliminated. Tubes can be strange things to deal with ....
« Last Edit: April 09, 2022, 04:31:21 PM by Mucker »


Offline Mykale

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Reply #2 on: May 28, 2022, 09:21:21 PM
After almost 2 months of being busy with life, I have come back to tackle the tube issue again. I have tried "cooking" the tube amp for 36 hours and it made no difference on the left side humming. I have also tried doing a light sanding of the contact pins and cleaning it with the isopropyl alcohol and there was no difference.

To clarify the left side humming, I would describe it as a medium volume hum that is unaffected by the volume knob and is present at all knob positions. Additionally, the hum is not there until the tube is warmed up and then there is sound that comes out of my headphones. The above humming follows the tube when doing mix-match testing with another Crack.

Is there any other suggestions or is the tube defective? Would I need to get another tube or does Bottlehead warranty the defective tube?

Thanks for all the help.


Offline Paul Birkeland

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Reply #3 on: May 29, 2022, 04:59:45 AM
You could try a replacement 12AU7 if running the tube in long term doesn't quiet it down for you.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Mucker

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Reply #4 on: May 29, 2022, 06:11:44 PM


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