My .50 cal+ is eating V-1 12ax7's like...

[scottcrud]

They're candy. Seriously, I've been through 3 in about 8 months. Starting with a NOS Jan Philips which sounded awesome for about a month, then a EH, which was so so, and now a JJ 803. Anyone heard of this before?

 

[LHanson]

Same valve position on all three?

 

[scottcrud]

yes, that would be the V-1 position. I'm a gain freak, I have the gain on 10 and use mainly the lead channel which V-1 is dedicated to.

 

[LHanson]

yes, that would be the V-1 position. I'm a gain freak, I have the gain on 10 and use mainly the lead channel which V-1 is dedicated to.

.50 Cal can be a gain feak amp. 8)

I dunno, bad solder connection to the heater of V1?

Do the tubes quit working, or just start sounding bad?

 

[scottcrud]

they just become microphonic and you can hear a low squeal.

 

[LHanson]

Does tuning down the gain a bit fix it? The older Boogie circuits can go into an oscillation in high gain situations. Maybe the plates are getting loose enough to vibrate after a period of time?

*gropes around in the dark*

 

[scottcrud]

Truth be told, I run the gain around 8-9 and this just started happening in the last year. Before preamp tubes would last a few years.

 

[RussB]

What you need to do is measure the voltages on V1. Look for any noticably burnt resistors or caps.

I don't know what the voltages SHOULD be, but a call to Mesa will verify if you're in the ballpark or not.

 

[RussB]

...now when you say "Eating Tubes" what does that actually mean?

Are they burnig up/shorting, or just going microphonic?
2 of the tubes are long-plate designs, and not so-to good in a high-gain combo application

 

[scottcrud]

it is a head version, not a combo, and they are indeed going microphonic.

 

[Boogiebabies]

You can get a reading of the resistor to the plate on V1. If the resistor is way off, like Russ said, it could be geting too much voltage and running the tube hard. I check all of mine at least once a year and so far all of my IIC's are at 248-259 volts on the v1 grid. Be careful if you try this. If you hit anything else in there you will get a big spark, a carbon deposit and an exploded 12AX7.

 

[scottcrud]

Thanks for the info guys, I'll just take it to Bill Ussery at Strait Music, he's the Boogie King here in Austin.

 

[Bren10]

Hey, Scott...
This is Brendon. If you want to bring it over, I can take a look at it. I agree that Bill would also be a good choice.