converting 6l6 amps to el84's

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pucho812

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anyone know what's inside products like the THD yellow jacket which converts  your amps 6l6 power tubes into an amp with el84's looks to me like it  it changes the pinout as well; as series resistors in key places..

here is a description


THD's Yellow Jacket converters not only rearrange the pin locations of the tubes, but also provide the necessary current limiting on the screens and cathode as well as blocking the amplifier's grid-bias voltage, configuring the EL84 in a Class-A, self-adjusting cathode-bias circuit.When the Yellow Jacket Converters are installed in larger amplifiers intended for 6L6s or EL34 output tubes, the high plate and screen voltages are reduced as well as current limited to protect the EL84 and to drop output power. When a pair of Yellow Jacket are used in a Marshall 50W or similar amplifier, the overall power drops to about 20W and takes on more of the character of an old Vox AC30. The distortion is smoother and more even and the output is both substantially reduced and more compressed due to the Class-A nature of the Yellow Jackets. In a 100W amp like a Twin Reverb or Marshall 100, either 2 or 4 Yellow Jackets can be used. If only 2 are used and the other 2 sockets are left empty, the output is dropped to about 20 watts. With 4 in place, the amp puts out about 40W and takes on a whole new warmth and richness.
 
hi!
I don't Know what's inside, but if Iwhere designing an el84 power amp, I'd certainly not except good performance from an amp with resistances in serie between tube and tx primary (as I don't see any other way to make an el84 from a 450V supply with only a gizmo in a socket-or is there some kind of active circuitry inside? I doubt about it). Also, I'd take care with impedance mismatch, as recomanded load can vary a lot from one el34 / 6l6 PP topology to another (I've seen things from 3K to 10K).
Also, this mood to take out 2 tubes out of 4 without taking care of the reflected load from speaker makes me sceptical...
and last, 40w out of 4 el84, seems borderline to me . (but marketers can easely make any 12mm buzzer spit 1KW, so...).
Obviously, it can work, but in any case?...
Just my humble, humble two cents...
Laurent.
 
thanks for that info.  seems like there is a little more going on then I thought but nothing that if I were to choose to I could DIY....  might just have him break down and buy the yellowjackets
 
I could imagene just a few components doing this...let me draw it up and the guru's can point out any errors of my thinking...
j
 
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grid bias on the oktal socket gets replaced with cathode bias on the noval socket end, and the signal ground is lifted by a Zener diode. all other connections are straight. anode to anode, screen to screen, heater to heater...
if this wouldn't work, I'm sure someone will point it out in a few hours....I never seen a yellowjacket, so this is just a hack..
J
 
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