Noob tube question :-/

[Draelyc]

The preamp in my Koch Studiotone uses three 12ax7s. Now, I know that the V1 input tube is usually the one closest to the input jack ~ natch. And I also know that the preamp tube closest to the transformer is usually the phase inverter, right? But the Studiotone is billed as being "class A." Does a design like that use a phase inverter? Or is that third tube just part of the gain/tone circuits in the pre?

Thanks!

 

[TP Parter]

No, class a amps (cathode bias like your ST, or single ended), don't use a phase inverter/splitter. It's for splitting the signal into two separate waves, which are then sent to the two sides of a push/pull class ab design.

I was almost a smart ass and used here let me google that for you, but I like you too much.

 

[TP Parter]

Check and see if it says tube fx loop, if so then you know what it is. Or it could be a reverb driver/return.

BTW, it's thenakedarab incognito.

 

[Draelyc]

No, class a amps (cathode bias like your ST, or single ended), don't use a phase inverter/splitter. It's for splitting the signal into two separate waves, which are then sent to the two sides of a push/pull class ab design.

I was almost a smart ass and used here let me google that for you, but I like you too much.

Much obliged ~ on both counts! I *figured* that was the case; just wanted to make sure. Hey, at least I labeled it a "noob" question...

 

[Draelyc]

Check and see if it says tube fx loop, if so then you know what it is. Or it could be a reverb driver/return.

BTW, it's thenakedarab incognito.

Your secret's safe with me!

Hmm, it might be additionalo gain stages for the od+ ...? I don't think the loop is tube buffered. Could be reverb, though, as you say.

 

[Sixtonoize]

No, class a amps (cathode bias like your ST, or single ended), don't use a phase inverter/splitter. It's for splitting the signal into two separate waves, which are then sent to the two sides of a push/pull class ab design.

I was almost a smart ass and used here let me google that for you, but I like you too much.

That's not entirely true.

Class A, Cathode Bias, and Single Ended are 3 completely separate things.

If the amp has 2 power tubes, it's very likely that it is Push/Pull, and as such needs a phase splitter.
The Vox AC30 is Class A, Cathode Bias, and is also Push-Pull. As such, it has a phase splitter.

Class A means that each power tube always reproduces 100% of the waveform, as opposed to Class B where each tube only reproduces the top or bottom half or A/B where the individual tubes reproduce most, but not all, of the waveform. Cathode Bias means that the idle current is set by resistors between the cathode and ground, as opposed to fixed-bias where the idle current is set by a constant voltage supply at the grid and the cathode is connected directly to ground. Single ended means that the output tubes are only connected to one side of the OT as opposed to Push-Pull where the OT is between the plates of the tubes.

Each of these three things is independent of the others. You can have Class A, single ended, and be fixed-bias, just as you can be true Class A, cathode bias, and Push-Pull. You can also be A/B and cathode bias...but Single -ended is out of the question because of the B in A/B.

The only way to really know how your amp operates is to ask the manufacturer or check a schematic.

 

[Draelyc]

No, class a amps (cathode bias like your ST, or single ended), don't use a phase inverter/splitter. It's for splitting the signal into two separate waves, which are then sent to the two sides of a push/pull class ab design.

I was almost a smart ass and used here let me google that for you, but I like you too much.

That's not entirely true.

Class A, Cathode Bias, and Single Ended are 3 completely separate things.

If the amp has 2 power tubes, it's very likely that it is Push/Pull, and as such needs a phase splitter.
The Vox AC30 is Class A, Cathode Bias, and is also Push-Pull. As such, it has a phase splitter.

Class A means that each power tube always reproduces 100% of the waveform, as opposed to Class B where each tube only reproduces the top or bottom half or A/B where the individual tubes reproduce most, but not all, of the waveform. Cathode Bias means that the idle current is set by resistors between the cathode and ground, as opposed to fixed-bias where the idle current is set by a constant voltage supply at the grid and the cathode is connected directly to ground. Single ended means that the output tubes are only connected to one side of the OT as opposed to Push-Pull where the OT is between the plates of the tubes.

Each of these three things is independent of the others. You can have Class A, single ended, and be fixed-bias, just as you can be true Class A, cathode bias, and Push-Pull. You can also be A/B and cathode bias...but Single -ended is out of the question because of the B in A/B.

The only way to really know how your amp operates is to ask the manufacturer or check a schematic.

Thanks, dude! I wouldn't be surprised if this amp is push/pull. I base that on nothing resembling electronic knowledge ~ it just seems more "modern" than "vintage," and I guess I connect that with push/pull... Be interesting to see if I can find any info online...

 

[Sixtonoize]

Actually, I would just about guarantee that it IS push/pull.

If you check the datasheet: http://tdsl.duncanamps.com/show.php?des=EL84

It shows that a single EL84 is Class A SE is going to put out around 5.7w.
Double that for two tubes, and you're still only getting around 11w.
You'd need 4 power tubes to get 20 watts out of a SE amp, unless Koch is pulling some crazy tube wizardry...and I'm not saying that that is impossible, just unlikely.

It doesn't show Class A PP in Pentode, but you can guess that you should be able to get 20w total, since you drop from 5.7 to 1.95w in Class A SE, so the increase from Triode to Pentode is likely to be similar in PP.

 

[Draelyc]

Actually, I would just about guarantee that it IS push/pull.

If you check the datasheet: http://tdsl.duncanamps.com/show.php?des=EL84

It shows that a single EL84 is Class A SE is going to put out around 5.7w.
Double that for two tubes, and you're still only getting around 11w.
You'd need 4 power tubes to get 20 watts out of a SE amp, unless Koch is pulling some crazy tube wizardry...and I'm not saying that that is impossible, just unlikely.

It doesn't show Class A PP in Pentode, but you can guess that you should be able to get 20w total, since you drop from 5.7 to 1.95w in Class A SE, so the increase from Triode to Pentode is likely to be similar in PP.

That makes a lot of sense, even to a layperson like me. Thanks, brutha!