why are these cathode based output tubes drawing so much?

[bob p]

yeah, after I posted that, I realized that I left the OP out of the list but I didn't think it was worth going back to add it. my bad.

[bob p]

Don't forget

4. Askers who are not Engineers and could benefit from simple straightforward answers.

I try to make my answers as straightforward as they need to be, without going overboard and being too wordy. Sometimes it isn't obvious whether an answer requires a simple chart or a detailed multi-paragraph explanation.

If you want to determine if your amp is operating in Class A, it is pretty easy to do:

Just drive a sine wave signal and look at the output on one side of the push pull circuit. if you see complete conduction of the sine wave then you have a 360-degree conduction angle and you're operating in Class A. Easy as pie.

If you have exactly one half of the sine wave then you have a 180 degree conduction angle and you're in class B.

If you have something in between, you're in class AB, which covers a pretty wide range (Pi to 2 Pi in radians, or 180-360 in degrees). Looking at the diagram that I posted in Post # 13, it's pretty easy to get a qualitative idea of whether your amp is operating in Class B, AB or A.

And to correct some disinformation that has been injected into the thread: I never said that measuring conduction angle was easy. Someone is trying to put words into my mouth to create an argument. What I actually said in Post # 13 was that it's easy to determine if your amp is operating in Class A. This post should demonstrate that looking at the plate waveform makes it pretty easy to determine your amp's operating class. Class A is the only operating class where you'll observe complete conduction of the AC waveform.

[Dave H]

If you want to determine if your amp is operating in Class A, it is pretty easy to do:

Just drive a sine wave signal and look at the output on one side of the push pull circuit. if you see complete conduction of the sine wave then you have a 360-degree conduction angle and you're operating in Class A. Easy as pie.

Bob as you know you need to look at the current output on one side not the voltage output (the voltage output will still be a whole sine wave) but I can't easily do that as I don't have a current probe and I don't want to risk destroying my scope by trying to use it in differential mode to measure across a plate resistor with 800V peak common mode on it.

The best I can think to do would be to scope across a cathode resistor as Nevetslab suggested. It would be plate + screen current but it will still give the conduction angle (according to LTSpice)

[bob p]

Yes, thanks for clarifying that. You do need to be looking at current. We've been talking about current all along, but that might be worth repeating. Both nevetslab (Post # 17) and the Aiken article had already specifically mentioned using a current probe in the setup, but I failed to reiterate that in my post. You're right -- it's an important point that bears repeating for clarification.

I agree -- the cathode resistor method mentioned in post # 17 is a very practical solution.

[Randall]

Lots of good information here. But, happy to report case closed. All it ended up needing is filter caps mounted on terminal strips under the chassis, and a 3 prong AC cord. Everything else checks out, and although the speakers do seem quite stiff, they are working. Thanks for the input once again! Close enough for rock and roll.

[Jazz P Bass]

To close out this thread: did you measure the amp current draw at idle & full out?

[g1]

3. Responders who are not trying to be helpful, and only taunt and make jeering comments from the sidelines as they behave like dickheads.

Seeing as that remark was directed at me, please re-read my simple question in post #15. Yes, it did include some light-hearted ribbing but was intended to further the discussion.
You came back with #20 which was the kind of condescending and dismissive tone that is unfortunately not all that uncommon for you.
If I was being a dickhead, I certainly was not the only one.
Apologies to Randall and other forum members for being subjected to this nonsense. I'm going to enjoy some new found freedom.

[bob p]

Seeing as that remark was directed at me, please re-read my simple question in post #15. Yes, it did include some light-hearted ribbing but was intended to further the discussion.
You came back with #20 which was the kind of condescending and dismissive tone that is unfortunately not all that uncommon for you.
If I was being a dickhead, I certainly was not the only one.
Apologies to Randall and other forum members for being subjected to this nonsense. I'm going to enjoy some new found freedom.

I don't like your repetitive lame-ass heckling from the sidelines. I was trying to help Randall, and what did I get in return? I got to listen to you heckling from the peanut gallery. Again. It's not the first time you've done this. Unfortunately, it seems from your attitude that this won't be the last time you do this.

You could have contributed to this thread with knowledge but you didn't. Instead of sharing your knowledge to work together in a community effort to help answer Randall's question, you only made two posts, both of which were noncontributory. They were nothing but cowardly wisecrack attacks that were directed as harassment.

Don't try to hide behind a facade of fake righteousness and try to shift the blame. I responded like I did in Post # 20 because I'm tired of the heckling that you are famous for. You're right, I was condescending and dismissive -- because I won't take any more of your shit. You can expect the same type of reply that I'm famous for every time you pull this BS in the future. Don't act surprised next time -- if you ask for a smackdown you'll get it.

[The Dude]

FWIW: IMO, No matter what the disagreement, name calling is out of line. In any open forum like this, there are bound to be disagreements. That's to be expected. But, calling people names should not be tolerated. This is getting a bit personal for my tastes.

[Randall]

Speaking for myself, G1 has always been informative and helpful to me. And I have never thought of his comments as anything other than good natured, including this time. The usual lack of aggressively worded posts is what makes this place unusual, and I for one would like to see it stay that way.