Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: nandrewjackson on February 11, 2019, 01:42:11 pm

Title: First try at Paraphase Inverter. Design stage, comments please.
Post by: nandrewjackson on February 11, 2019, 01:42:11 pm

https://drive.google.com/open?id=1ojs25lVTUMKRHCMd3wpYewpJxsLkvjXW

Hello,


I've got a new project in mind, and I've got all the parts needed to begin.


It'll be my first attempt at a paraphase inverter. 


I'm shooting for a 2 - 6L6 push pull power section with only a single 12AX7 providing the preamp and phase inverter.


The first triode is essentially 5F2A Princeton, then the second triode will be a paraphase inverter triode.  I've successfully built plenty of long tail phase inverters, this will be my first paraphase.  I've researched ValveWizard, and Hoffman's Library to come up with this.


Any thoughts?  Comments?  Suggestions? 


Thanks,
Noah P

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: sluckey on February 11, 2019, 01:48:35 pm

That's a cathodyne PI, not a paraphase PI. Not gonna be enough signal to drive those 6L6s.

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: 2deaf on February 11, 2019, 04:01:15 pm

The volume control and tone control are not going to ground.  They are going to a point that has almost as much signal as the grid has.  This means that there is going to be very little current flowing in those circuits until the wipers are turned way down.  With very little current flowing, the controls are going to do very little. 

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: PRR on February 11, 2019, 07:25:31 pm

> I've researched ValveWizard, and Hoffman's Library

Steal more carefully.

Even if you meant to type "Cathodyne", this one is troubled.

Or just build it. You will be disappointed.

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: nandrewjackson on February 11, 2019, 09:49:35 pm

https://drive.google.com/open?id=1s7qmPhOrYKfoVusbBMjHb7AbweZiBmUx




Apologies about the paraphase/cathodyne confusion. 


OK, I guess I'll stick with what I've previously got to work.


I'd really like to only use one 12AX7, but if that's not possible, then,


What kind of voltage divider do I need between the second triode and the long tail phase inverter?
All of my other builds have had CF into long tail.  I REALLY DON"T WANT TO USE a 3rd 12ax7


Thanks in advance,
Noah

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: sluckey on February 11, 2019, 10:00:31 pm

Maybe something simple like this...

http://sluckeyamps.com/misc/AB763_Deluxe_Lite.pdf

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: PRR on February 12, 2019, 12:12:24 am

> I'd really like to only use one 12AX7

Rule of thumb:

You need two *gain* stages to get from guita to 6V6/6L6 grid.

For push-pull, you need a 3rd stage to make the second output.

So you need 3/2 of a 12AX7.

The "3rd stage" can be a high voltage MOSFET "cathodyne".

Or the 1st stage "can" be a low voltage JFET, or even a hot booster-pedal.

There are other paths but they all seem to involve "more parts". A pentode "can" give more gain in one stage (often too much) but has more bits inside the bottle to wire-up. You can put JFETs and MOSFETs all over the place... but is it a tube amp?

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: nandrewjackson on February 12, 2019, 02:51:18 pm

 :icon_biggrin:
Ok, thanks everybody.
I'll stick with 2 triodes into a long tail. I wanted to find a single preamp tube solution, basically as a novelty idea, but oh well.


Thanks again

Title: Re: First try at Paraphase Inverter. Design stage, comments please.
Post by: sluckey on February 12, 2019, 03:08:34 pm

There are some single preamp tube solutions ***IF*** you are willing to step down from 6L6s to much lower powered  6BM8 or 6GW8s. These tubes contain one triode and a power pentode. So, you can build a push/pull power with LTP PI with only two power tubes. A single 12AX7 or an EF86 pentode will drive that power amp nicely.