Dead preamp tube?

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nlaplante
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Dead preamp tube?

Postby nlaplante » Sat Oct 15, 2011 9:26 am

Hi everyone,

I recently put a Tung-Sol 12AX7 in the V1 position of my JSX head. Everything was ok until I decided to test the outcome of putting it in various positions.

When I tried to remove the tube from V1, it was very difficult. The tube was stuck in there. I finally managed to get it out and put it in V2.

Powered up the amp, and I was getting no sound at all. I switched it to V3 (which is the fx loop and active eq I think) and I was getting sound. But as soon as I engaged the FX loop, the sound was gone.

Do I have a faulty tube? I see its filament light up a bit but not as much as my other preamp tubes.
Be someone

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thunda
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Re: Dead preamp tube?

Postby thunda » Sat Oct 15, 2011 10:35 am

that tube has a spiral filament encased in the plate structure, it won't glow as brightly as other tubes. That being said, there is a problem with Russian made spiral filament tubes when used in cathode follower positions. V1 is not a cathode follower. But I am unsure of the other positions in your amp. Many times, particularly with Mesa amps, the tube will fail almost immediately when placed in a cathode follower position (as in V4 in my Heartbreaker, for example).

Hope this helps.
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(heart) le Peavey
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Re: Dead preamp tube?

Postby (heart) le Peavey » Sat Oct 15, 2011 11:45 am

If V1 was the last position that worked, have you tried it there again?

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Van Noord
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Re: Dead preamp tube?

Postby Van Noord » Sat Oct 15, 2011 10:52 pm

I would try it in V1 again and see the result.
I believe V3 is the Cathode Follower stage in the JSX (maybe Enzo can confirm). One time I put a Sovtek LPS in the V3 spot of my JSX and the tube failed almost immediately.

I didn't care for the Tungsol 12AX7 in V1 of my JSX. It was too bright and a little noisy.
The absolute best I've found to use are JJ ECC83S's in V1,V2,&V3 and a Russian tube in V4, either a Sovtek or EH.
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Classic30inCincy
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Re: Dead preamp tube?

Postby Classic30inCincy » Sun Oct 16, 2011 8:23 am

Tubes can & will fail.......

IF you purchased tube new request exchange.

Tube manufacturers generally provide 60 day warranty.

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Enzo
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Re: Dead preamp tube?

Postby Enzo » Mon Oct 17, 2011 6:02 pm

There is no cathode follower in the JSX. The only stage with a cathode at any voltage to speak of would be the phase inverter, and that shouldn't be near enough to trouble any 12AX7 model.

The tube was probably damaged. Try a different tube, grab one out of another amp if you need to.


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