Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Boone on October 23, 2013, 05:03:57 pm

Title: 12ax7 safe voltage
Post by: Boone on October 23, 2013, 05:03:57 pm

I have tweed princeton - 12AX7 V1 at : pin one 200.4V and pin 6 at 204V. Will this high of plate voltage prematurely wear out the tube? Thank you for the help

Title: Re: 12ax7 safe voltage
Post by: HotBluePlates on October 23, 2013, 05:21:22 pm

Not in the least. MANY tube amps have much higher voltage on their 12AX7 plates

Title: Re: 12ax7 safe voltage
Post by: Boone on October 23, 2013, 05:32:29 pm

Thanks hotplates. Another reading: the 6V6 is at 356 on pin 3 and 333V on pin 4. I am running NOS 50's Sylvania in there now. Is that safe without premature tube failure as well?

Title: Re: 12ax7 safe voltage
Post by: HotBluePlates on October 23, 2013, 05:33:28 pm

Yep, just fine. And about 70v lower than some Fender amps.

Title: Re: 12ax7 safe voltage
Post by: Boone on October 23, 2013, 06:00:13 pm

Thanks for the input. I appreciate it

Title: Re: 12ax7 safe voltage
Post by: tubeswell on October 24, 2013, 03:58:49 am

This is a good read on triode characteristics (a 12AX7 is a 'dual triode') http://www.valvewizard.co.uk/Common_Gain_Stage.pdf (http://www.valvewizard.co.uk/Common_Gain_Stage.pdf)

You will find some information on typical 12AX7 ratings on pages 33-35 (which should provide a fuller answer to your question)