Frequently Asked Questions

How do I know which Yellow Jacket® converter to pick?

If you are in doubt, you may e-mail and we will help you decide.

The YJS is for amplifiers with fixed bias power tubes. Fixed bias power tubes have their cathode connected directly to ground and a negative DC voltage applied to their control grid. The negative bias voltage is usually adjustable by way of a bias pot.

The YJC is for amplifiers with cathode biased power tubes. (This is often referred to as self-bias or auto-bias because it does not require a bias pot adjustment when tubes are changed). Cathode biased power tubes will have a resistor and bypass capacitor connected in parallel from their cathode to ground, as seen with most preamp 12AX7 triodes. The ground wire is used to bypass the amp's original cathode bias components so that the Yellow Jacket® converter's internal bias components are used instead.

The YJ20 is like a YJC that does not drop the plate and screen voltages. It is meant for use in lower power output amps (20W or less) when no power reduction is desired. It comes with a ground wire for cathode biased amps.

The YJUni is a direct pin to pin converter with no internal voltage dropping or bias components. It is meant for use in lower power output amps (20W or less) when no power reduction is desired and you would prefer to use the amp's original cathode bias components.

The YJ7591 is for amplifiers that use 7591 power tubes. Only the triode version will provide a power reduction. It comes with a ground wire for cathode biased amps.

What is the difference between the normal and triode versions?

The triode version provides a greater power reduction and more linearity than the normal (pentode) version.

Most guitar amp power tubes are pentodes, meaning they have five electrodes:

  1. cathode
  2. control grid
  3. screen grid
  4. suppressor grid (or beam confining electrode)
  5. plate

Power tube triodes like the 300B (more common to hi-fi stereo) have three electrodes:

  1. cathode
  2. control grid
  3. plate

Pentodes can be wired to behave like triodes by connecting the supressor grid directly to the cathode and the screen grid to the plate through a current limiting resistor.

Do certain amps perform better with the triode?

This is a matter of personal taste. The triode version will provide a greater power reduction and is more linear (less distortion) than the pentode. If you're looking for the maximum power reduction and want to tame the response of your amp a little, then go for the triode. If you'd like a power reduction, but want a response with more bite and attitude, then go for the pentode.

I have VHT super 6 combo amp. It says it's cathode biased Class A. What Yellow Jackets® adapter can I use in place of the 6V6GT?

For a single-ended cathode biased 6V6GT, you can use the YJC, YJ20 or YJUni.

The YJC will give you a bigger plate and screen voltage drop for more of a power reduction at high amp volume settings.

The YJ20 will not drop the plate or screen voltage so that there is no power reduction.

The YJUni is a direct pin to pin converter with no internal voltage drop or cathode bias circuit which means you will be using your amp's cathode bias and screen circuit.

Can the YJS, YJC and YJ20 be used in Class A amps?

Yes. They can be used to convert class AB outputs to class A, but they are definitely good for allowing the use of EL84 tubes in Class A amps (Single-Ended or Push-Pull).

I installed your YJS Triodes in my Fender Blues Deville and was expecting to hear a 70% to 90% decrease in volume, but I don't hear it. What gives?

There are two ideas to consider here.
1.) A 90% power output drop does not mean a 90% drop in volume. You actually have to reduce power output by a factor of 10 (i.e. 90%) to hear half the volume. For example, a 60W amp at full volume puts out 6W at 1/2 volume, 0.6W at 1/4 volume, 0.06W at 1/8 volume, etc.
2.) The YJS Triodes in your amp have reduced the maximum power output of 60W to about 6W. If you had the amp set for 3W output power before installing the Yellow Jackets® adaptor, you will still have the same 3W output and will not notice a volume difference until you turn it up to at least 6W.

Can I use any other tubes besides EL84 with the Yellow Jackets® adapters?

You may use other direct substitutes for the EL84 including 6BQ5, E84L, EL844, 7189, 7189A and 7320.

I have a vintage Music Man RD-50. It has cathode driven 6L6GCs. Can I use any of the Yellow Jackets® adapters?

No. The Yellow Jackets® adapters will NOT work with cathode driven power tubes.

I have a Marshall Major. It has really high plate voltages. Can I use any of the Yellow Jackets® adapters?

No. We do not recommend using Yellow Jackets® adapters in amps that are rated for more than 100W power output or that have more than 519V on the power tube plates.

I have a Fender Hot Rod DeVille. It has a 1 ohm resistor and diode connected to from the power tube cathodes to ground. Do I have to use the YJC and bypass these components?

It is not necessary to use the YJC in this amp. The 1 ohm cathode resistor is for measuring bias and does not present any problems for the Yellow Jackets® adapter internal cathode bias circuit.

Do Yellow Jackets come with a warranty?

Yes! ALL Yellow Jackets have a one year Warranty against manufacturer defects.

Where are Yellow Jackets® converters manufactured?

Yellow Jackets® converters are manufactured in the United States.