Yet Another Tube Question: How to bias a Cathodyne Phase Inverter for 12 volts

[frequencycentral]

Ok, next question:

How do I bias this for 12 volts please? I just don't know the math. I think the 10k resistors are correct. What about the other two?

I've been staring blankly at this page for an hour: http://www.valvewizard.co.uk/ (The Cathodyne Phase Inverter)

[DougH]

I have not played with cathodynes but this may be a good place to start: http://www.aikenamps.com/TI_Aiken_adv.htm

You are basically going to have to design a cathodyne stage for the supply voltage you want to run at. This involves plotting a load line, picking an operating point, and running some simple Ohm's Law equations. Look at Aiken's article on designing long-tailed pairs using a load line. Once you understand that, you should be able to apply similar ideas to the cathodyne. The valve wizard article is good too, but you may need some practice designing using load lines first.

[frequencycentral]

Thanks Doug. OK, I think the 150R should be 1k. Seems to work. I hate math!

[JDoyle]

Thanks Doug. OK, I think the 150R should be 1k. Seems to work. I hate math!

I know you don't want to hear this but you really have to use math.

The whole basis of electronics is an equation.

Regards,

Jay Doyle

[sean k]

I remember having acces to some articles, on the net, written in the fifties or sixties that explained all the stuff around building your basic tube amp with push pull outputs and even designed and built an amp I still use. Trouble is the links for the articles were on my PC that crashed and the printouts I've got are... somewhere!
The articles explained basic work with loadlines and it's really quite simple. I always found it harder doing the power supplies and plotting all the resistors and caps to get specific voltages at specific loads... that was always a pain. Load lines are the fun bit and theres far more pencil and paper work with the points on the loadline graphs, plotting voltage swing, than there is using ohms law.

Now if only I could remember who the author of those articles was. What I do know is that I found them wandering around stereo tube amp sites and not guitar amp sites.

[frequencycentral]

Next question: Is there any reason that a Cathodyne Phase Inverter should not invert when using a 12 volt power supply? Is there a minimum voltage you have to give it to make it do its thing?

[frequencycentral]

Ok - answered my own question - I just rigged up a MAX1044 to give me 44.2 volts from a 11.91 volt input. I'm getting an inverted signal. Hurray - and the crowd goes wild!

EDIT: I'm using a triangle wave test oscillator, at 44.2v it comes out perfectly balanced, as I drop the voltage it become unbalanced and loses shape.

[frequencycentral]

Just thought I'm post some images of the shape/symmetry of a triangle wave run through a tube inverter at different voltages using a MAX1044. As I'm working on a vibrato and phaser, it looks like the higher the voltage the better.

[frequencycentral]

For those interested, this is what I've come up with so far:



Hopefully this will be the first stage of my tube vibrato, and will also form the basis of my tube phaser.

Here's the (stereo) output I'm getting at pin 8 and pin 5 of the second triode.



When I mix the two signals I'm not quite getting full cancellation, but pretty close - a 30db drop in level.

I do feel that I'm talking to myself here though..............

[petemoore]

I do feel that I'm talking to myself here though
  And you have some nice results and graphs as a result !
  Is the intent of cancellation simply to test the phase inversion symmetry / accuracy ?
  Phase Shifter you said ?
  How many tubes would that be? [youch#?].
  I think the consensus is in, if voltage matters and can be higher, tubes preferred it to be somewhat higher...mostly, and unless you are not looking for starved plate characteristics.

[frequencycentral]

I do feel that I'm talking to myself here though
  And you have some nice results and graphs as a result !
  Is the intent of cancellation simply to test the phase inversion symmetry / accuracy ?
  Phase Shifter you said ?
  How many tubes would that be? [youch#?].
  I think the consensus is in, if voltage matters and can be higher, tubes preferred it to be somewhat higher...mostly, and unless you are not looking for starved plate characteristics.

Thanks Pete, I'm really pleased with the results I've achieved today.

Yeah, the symmetry/accuracy of phase cancellation needs to be pretty good for vibrato or phasing.

The Vibrato should be two tubes, the phaser two or three depending how many stages gets a good result. the MXR Phase 45 is only two stage though, so maybe I'll get away with just two tubes. For a Phase 90 equivalent it would be four stages and therefore three tubes. I'm using 6111 submini tubes, so no problems of lack of space within the pedal enclosure.

I'm running the plates at 44.2 volts, derived from a MAX1044 with three stages of voltage increase, from the Geofex site. See the other graphs above for the results at different plate voltages.

Rick

[comfortably_numb]

What triodes are you using?  The 12u7 was meant to be used at 12 volts from a car battery.  It's what I'm designing with, though I don't have any yet and can't comment on the sound.

[frequencycentral]

What triodes are you using?  The 12u7 was meant to be used at 12 volts from a car battery.  It's what I'm designing with, though I don't have any yet and can't comment on the sound.

I'm using 6111 submini tubes - built a Subcaster with one a while back, really nice sound. Basically a 12au7 but in a tiny package. 6.3 volt heater requirement, but you can run two heaters in series from 12 volts. Also, they fit into the breadboard really nicely, just like slotting an I.C. in.