[K31TH3R]

So I recently bought a Nobsound Little Bear P10: https://www.amazon.com/Multi-Hybrid...id=1542257306&sr=8-1&keywords=little+bear+p10

After a bias adjustment it's a great sounding amp even with the stock Shuguang 12AU7 tube.

I wanted to see what another tube did to the sound, so I ordered an Electro-Harmonix 12AU7 balanced triodes: https://www.amazon.com/gp/product/B079MFGGGY

Before I installed it I set the bias back to the factory settings, and when I powered the amp on and it came up to temperature and started running, everything was crackling terribly with any volume. It sounded okay at low volume, but as soon as I turned up my source or the amp, it would break up and crackle really bad. Like loud, aggressive crackles much louder than the music.

I'm new to tubes, but I read that it takes a new tube about 30 minutes to stabilize, so I left the amp on at low volume to get some heat into the tube and after about 30 minutes of running I checked the tube and it was at 175f (IR probe)

I adjusted the bias until I got it sounding really nice for about 5 minutes. However, before I could really analyze whether or not it sounded better than the Shuguang, it once again started distorting really badly. I figured the tube was ready for another bias adjustment after breaking in, but no matter where I run the bias, cold or hot, there is distortion. I either get crackles, or distortion.

When the tube sounded good briefly, the bias needed to be quite a bit colder than the Shuguang. I assumed this was because it still needed breaking in.

The tube does specify that it's a 12AU7A, however, I read that electrically the 12AU7 and 12AU7A are the same, and they're only not interchangeable if the amp specifically requires a 12AU7A. Is this incorrect?

Any help would be appreciated. BTW, if I switch back to the Shuguang 12AU7 the amp still sounds fantastic. Did I just receive a bad tube?

Thanks for any help.

 

[K31TH3R]

One more thing.... There's no red plating going on, nor is there any violet coloration that suggests there's air getting into the tube. The Shuguang tube runs at about 160f, so this one is definitely a little warmer. Not sure if that helps at all...

 

[Keno18]

One more thing.... There's no red plating going on, nor is there any violet coloration that suggests there's air getting into the tube. The Shuguang tube runs at about 160f, so this one is definitely a little warmer. Not sure if that helps at all...

How long ago did you buy the amp? If you can return it I would. I bought a p1 and the quality was awful. The first board had thermal problems, it was replaced but the muting relay was bad on the second. I had much better success with the Bravo V2. It doesn't have a bias adjustment, but it just works reliability and sounds great. The 12au7a EH is a good tube. I use it myself.

 

[K31TH3R]

Thanks for the reply about the 12AU7A EH, the Bravo V2 is a similar mosfet design to the P10, so it would seem I just received a bad tube if that tube works good for you in the Bravo V2.

The only reason I didn't go for the Bravo V2 is because I liked the rear input/output on the P10. I'm using it as a pre-amp for my Pimeta to color the sound a bit and add that classy tube warmth, and I didn't want any wires coming from the side/front.

I've had the P10 since Saturday the 10th. I'm actually really happy with it. My only complaint was the heat, so I built myself a little 7v 60mm USB fan that I run on 5v. It's silent and it brought temps down from 105c to 60-70c.

But I have until Jan 31st to return it, so we'll see if it stands up.

 

[Keno18]

Thanks for the reply about the 12AU7A EH, the Bravo V2 is a similar mosfet design to the P10, so it would seem I just received a bad tube if that tube works good for you in the Bravo V2.

The only reason I didn't go for the Bravo V2 is because I liked the rear input/output on the P10. I'm using it as a pre-amp for my Pimeta to color the sound a bit and add that classy tube warmth, and I didn't want any wires coming from the side/front.

I've had the P10 since Saturday the 10th. I'm actually really happy with it. My only complaint was the heat, so I built myself a little 7v 60mm USB fan that I run on 5v. It's silent and it brought temps down from 105c to 60-70c.

But I have until Jan 31st to return it, so we'll see if it stands up.

If you're using it to just color the sound, take a look at the FX-AUDIO Tube-01. It's a tube buffer/preamp made just for that purpose. It's only $31.99. I'm using it ahead of a Schiit Audio Magni 3 to give the Magni a tube sound. Very well built and has gotten good reviews.

 

[K31TH3R]

Thanks for the recommendation. I like the look of that, and the price as well. Have you tried any other tubes than the 12AU7A EH? Any favorites?

 

[Keno18]

Thanks for the recommendation. I like the look of that, and the price as well. Have you tried any other tubes than the 12AU7A EH? Any favorites?

Definitely the RCA 12au7a clear top also known as the side getter. My main amp is now the Schiit Vali 2 but even though it takes tubes from the 6dj8 family I still use the clear top with an adapter.The tube is still reasonably priced even though it's about 50 years old. The easiest place to get it from is partsconnexion.com at $9.97 a piece. I can't recommend it highly enough. Silky smooth highes and outstanding low end with great imaging and soundstage.