Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: JesseJJ101 on April 16, 2019, 02:28:04 pm

Title: Valve junior conversion to ax84 extreme with a el34
Post by: JesseJJ101 on April 16, 2019, 02:28:04 pm

Hi Guys!

I plan (Hope) on building a ax84 p1 extreme. For that I would like to use the PT of a valve junior I have lying around but im not quite sure if this would work out. The valve JR PT has 260-0-260 for high voltage while the p1EX schematic calls for a 275-0-275 (Hammond 370dx) or a 369ex wich has completely different voltages. So Im not quite sure about that.

I was wondering if anybody has experience with a Valve JR powering a 12ax7 and a el34 and if that works out current wise. Also what would lower transformer voltage result in. Any help is much appreciated!

Kind regards!

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: Papa Jim on April 16, 2019, 05:57:06 pm

http://thesubjectmatter.com/calcptcurrent.htm   Hope this helps ya out.

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: PRR on April 16, 2019, 10:12:24 pm

Welcome.

It will have power similar to the stock Jr.

Gain and "flavor" will be different, I assume. Notably more knobs, more mid-scoop, and the option to overdrive the preamp without letting loose the Jr's big 5 Watts.

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: st on April 17, 2019, 12:11:17 am

Are you sure the stock pt provides enough heater current?
Edit: I don't think so...

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: PRR on April 17, 2019, 01:07:17 pm

I hope the "EL34" is a typo for EL84.

The '34 beast has no place in a Jr.

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: st on April 18, 2019, 12:04:00 am

Nope. The p1 extreme is a single ended el34 amp, and therefore won't work (for long) with the vj's iron.

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: PRR on April 18, 2019, 12:14:20 am

> The p1 extreme is a single ended el34

I see you are correct.
http://ax84.com/static/p1x/AX84_P1x_101004.pdf

Yup, needs new fatter iron to do that.

No real reason he can't use the AX84 eXtreme preamp stages with the Jr's stock EL84 power stage. Get some more/different sounds than a pure Jr.

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: st on April 18, 2019, 01:03:13 am

Quote from: PRR on April 18, 2019, 12:14:20 am

No real reason he can't use the AX84 eXtreme preamp stages with the Jr's stock EL84 power stage. Get some more/different sounds than a pure Jr.

That's definitely what I would do if this build is to happen in the Jr's chassis.

Title: Re: Valve junior conversion to ax84 extreme with a el34
Post by: MakerDP on April 18, 2019, 09:04:33 pm

The original P1 has the EL84 output stage. No reason you couldn't match the preamp of the P1eX with the power amp of the P1 to get a perfect match for a major Valve Jr. upgrade.

Heh, now you got me looking for a Valve Jr for myself. Sounds like a fun project.