yellow jackets, tone bones???? class A???? true or fake????

[fatboy135]

Well from some years ago I know that there are an adapters that externally fits el84 tubes on other tube sockets, well I could believe that they could arrange from pentodes to tetrodes, I could also believe that they could rearrange all voltage and current parameters on the tube with some resistors, but I can´t understand when they said that they could convert your amp from a push-pull into a class A, that is big fake.
Let me explain it, the bias point fixed our amp working zone for example in a class A mode both half sinus waveforms are amplified in the same amount, for that reason we need to fix the bias point just in the middle of our tube datasheet curves.
A class AB amp just split the signal into the two sinus waveforms, and one of them is amplified with one tube and the other half by the other tube, ok the tube that splits the signals is the phase splitter tube, just the last into the preamp tube chains.
So here is my question: How is it possible that yellow jackets takes your amp into a class A if the yellow jacket is just after the phase splitter ????
If I really want to get the class A I need to skip the phase splitter tube or rejoint the two phases after that phase splitter, but as I could see that tone bones only fits into the power tube sockets and doesn´t relays or switch any other path that could rejoint the two halfs. Could anyone explain it to me???? I´m really astonished with such invent

 

[ylo]

You are correct. I would call "Class A" a big lie, or at least a big marketing misnomer.

Yellow jackets convert to cathode bias. In music industry marketing parlance, cathode bias is now called "Class A." I don't know who started this, but the Vox AC30 is held up as the shining example of "Class A."

All guitar players believe that "Class A is desirable, even though few have heard it or have a clue what it is from a technical standpoint. Industry marketing weasels have determined that they must offer "Class A" or they might lose amplifier sales to competitors, so they all claim to offer it. Few actually do.

The tube amp gurus over at alt.guitar.amps state that NONE of the "Class A" guitar amps actually operate in Class A except for amps with single-ended output stages (NOT push-pull). From my somewhat limited understanding of tube circuits and my old tube text books, I believe them. The LSS in 5 W mode would seem to qualify as Class A, although I have not seen the circuit diagram or measured the operating point.

Yellow Jackets may or may not sound good to you in your amp. Keep in mind that your output transformer may not be ideal for the particular tubes used in the Yellow Jackets, and the tone stack in your amp's preamp may not be voiced ideally either. As you surmised, the EL84 versions simply convert to EL84 with cathode bias through resistors and capacitors. You could do the same to your amp yourself, but the advantage of the Yellow Jackets is that you just plug the suckers in, no need to hack up the innards of your amplifier's output stage.

Check the web for opinions on Yellow Jackets in your particular amp.

 

[nomad100hd]

a push pull amp can be class a, but as ylo said most amps that advertise as class A are not class A. However wether an amp is class A or not is purely determined by it's bias. At least that's what i've been taught, on forums.

 

[ylo]

The AGA guys claim that not one commercial push-pull guitar amp operates Class A.

Class A or whatever, all that really matters is the sound of the amp, not the marketing hype! I'm a fan of the Lonestar Special regardless.

 

[gonzo]

i use groove tubes substitubes in my mesa mark2b.

two 6l6's become 2 el84's.

they work amazingly well, break up much earlier than the 6l6's, offer a different gain structure (think mark2b married with a vox ac30), and take a load of stress off the transformer.

i compared these with the YJ's, and these were much better to my ears.

they feel substantially stronger physically, as well.