How does the phase inverter work in a tweed deluxe

[d. spree]

I have a question that is pretty basic. I understand that in the tweed deluxe one triode of the V2 tube works as the phase inverter - splitting the signal and sending two out of phase signals to the output tubes. How does the one triode do this?

[JoeM]

Good explanation here:

The Valve Wizard

[d. spree]

Good explanation here:

The Valve Wizard

Thanks Joe - read it. But having only built 3 amps I'm looking for something more basic - in very ordinary English.

[JoeM]

Honestly, I think the article explains it pretty well. Is there something more explicit that it doesn't cover? Maybe the terminology is confusing?

[Steve A.]

I have a question that is pretty basic. I understand that in the tweed deluxe one triode of the V2 tube works as the phase inverter - splitting the signal and sending two out of phase signals to the output tubes. How does the one triode do this?

The way I understand it the phrase inverter works by turning the phrase "tube amp" into "amp tube" and so on. Or am I missing something here?
[Sorry- things like this are always popping into my head and no offense was intended towards the OP who asked a good question.]

Steve

[jazbo8]

I have a question that is pretty basic. I understand that in the tweed deluxe one triode of the V2 tube works as the phase inverter - splitting the signal and sending two out of phase signals to the output tubes. How does the one triode do this?

It is simply the property of the vacuum tube - the grid is your input, and the plate or the cathode can be used as outputs, so with a single triode in this case, taking the signal off the plate give you opposite polarity and the cathode give you the same polarity signal with respect to the grid, i.e., the plate and cathode are always out of phase with each other.

[Enzo]

Do you understand how a basic triode stage works? Like the amp's input stage? And so do you understand why the signal at the plate is opposite in polarity from the one at the grid? If not, we can explain it pretty simply.

And do you understand a cathode follower?


This phase inerter is both those things in one stage. The signal at the plate is inverted from the grid input and is used for one power tube. The signal at the cathode follows the grid, ie is the same polarity, and is used to drive the other power tube.

What about this is not working for you.


Allow me an analogy. The grid on a tube controls how hard it conducts between plate and cathode. The more positive we bring the grid, the harder the tube tries to pull the plate and cathode together - or reduces the equivalent resistance between them. Now imagine you are exercising for fitness. You can lie on the floor, tense up your abs and it makes you sit up. The muscles pulled your head towards your waist. Now lie back flat, and this time flex your abs and it makes your legs rise into the air - they pulled your feet closer to your waist. Now do some crunches. That is a combination of both, you are bringing your head and knees toward your waist at the same time.

Your tube is like your abs. A positive signal on the grid is like crunching your abs. It pulls the plate down and the cathode up. That means the signals at those two points are opposite in polarity - one is going up while the other is going down.

[eschertron]

Your tube is like your abs. A positive signal on the grid is like crunching your abs. It pulls the plate down and the cathode up. That means the signals at those two points are opposite in polarity - one is going up while the other is going down.

...and the taser on your abs is like the grid signal! Yesss!

[d. spree]

Thanks all. I did figure it out last night at home. Your explanations are great, I just had to figure out that the tube splits the signal - inverts one of the signals and outputs them through the cathode and plate to each of the output tubes. It was when I traced the wiring diagrams etc that I figured it out. But, again thanks for your help. I had read Dave Hunter's book but as his most detailed descriptions of circuits was based on the Princeton there was no detailed discussion of how the phase inverter worked.

My question is a good example of how it is relatively easy to build an amp and not really understand a whole helluva lot about them.

[Enzo]

That's true. Building an amp teaches a lot about tool use, and the mechanics of electronic parts, but it doesn't get to teach you much about circuits. But it does help familiarize you with layouts and maybe makes it easier to put circuit learning into useful context.

[Dave H]

The tube inverts the signal because the plate connects to B+ through a resistor but the cathode connects to ground (through the same value resistor). When the current through the tube increases (say) the plate voltage falls because of the increased voltage drop across the resistor to B+ but the cathode voltage rises because of the increased voltage drop across the resistor to ground. The cathode voltage rises as the plate voltage falls i.e they are out of phase. It’s not the tube, it’s the way it’s connected, replace the tube with a transistor or FET and it would still work in the same way.

[d. spree]

The tube inverts the signal because the plate connects to B+ through a resistor but the cathode connects to ground (through the same value resistor). When the current through the tube increases (say) the plate voltage falls because of the increased voltage drop across the resistor to B+ but the cathode voltage rises because of the increased voltage drop across the resistor to ground. The cathode voltage rises as the plate voltage falls i.e they are out of phase. It’s not the tube, it’s the way it’s connected, replace the tube with a transistor or FET and it would still work in the same way.

Wow, that is a neat and concise explanation. Thanks.

As Enzo agreed earlier "Building an amp teaches a lot about tool use, and the mechanics of electronic parts, but it doesn't get to teach you much about circuits. But it does help familiarize you with layouts and maybe makes it easier to put circuit learning into useful context." I have built 3 tweed deluxe amps - 2 I use and one for a luthier friend. The first build used a tube depot kit and I chose that because i was totally concerned about getting the components in the right place. I learned nothing about the amp at all, and just had top follow very detailed instructions. Once done it sounded really good - but I was really bothered by the fact that the guts were not "authentic" - the PCB board for example, and the PT (not authentic values) etc etc. Even with the back on the amp I know what's inside!

The next two I used Mission parts with some substitutions. Felt much happier - these amps (one of which I gave away) simply sounded better (less hum and generally a "fuller sound" - I know that's subjective but I don't think its purely because I know what's inside. In retrospect I wish I had started with the Mission and not worried that I needed incredibly detailed instructions - the tube depot kit comes with about 60 pages of photos and instructions.

After I finished my 3rd build I realized how much I still did not know - did learned something in between - read up on how tubes work, and due to having to troubleshoot a bit learned about how pots work etc. After that I started reading Dave Hunter's book - which I really enjoyed but which I still felt left me with a lot to learn. I still am having to learn to read schematics (and it bothered me that he jumped quickly to showing schematics without an in between step of talking about how to read them) and compare then to the actual circuits I am looking at. So I've got a long way to go. I am now examining my builds and tweaking and trying to learn the electronics and some theory behind them. But thanks everyone for your help. This forum is a really amazing resource and I have sought and received tons of great advice here.

[Tom Phillips]

…I am now examining my builds and tweaking and trying to learn the electronics and some theory behind them. But thanks everyone for your help. This forum is a really amazing resource and I have sought and received tons of great advice here.

Following are links to some discussions about books that contain the kind of information you seek. Learning the basics gives you the foundation needed to understand discussions and books at the next level and then the next and higher. You also gain the knowledge to know when something just doesn’t make sense or breaks the laws of physics. AKA when someone is spewing BS.
http://music-electronics-forum.com/t33527/
http://music-electronics-forum.com/t1197/
http://music-electronics-forum.com/t12215/
http://music-electronics-forum.com/t23258/
I’m sure there are more too.

HTH,
Tom