Yellow Jackets® converters are a type of specialized adapter which permit the use of EL84/6BQ5 power tubes in place of 6V6, 6L6, EL34, and 7591 type vacuum tubes.
Yellow Jackets® converters allow you to harness the musicality of EL84 vacuum tubes in amps that don't use them already - it's like getting a whole new amplifier! In place of a 6V6 a Yellow Jackets® converter will even out the tone and make it sound stronger. In larger amps that use two 6L6, 6550, 7027 or EL34 power tubes the Yellow Jackets® converter will drop the output power to about 15 to 20 watts, giving it more of a vintage VOX AC30 sound. In amps that take four power tubes the Yellow Jackets® converter will sweeten the tone and make it more dynamic. There is no rebiasing involved, which makes modifying your amp's tone very easy.
Yellow Jackets® converters give you simple Class-A operation from any amp. They not only rearrange the pin locations of the tubes, but also provide the necessary plate voltage drop and current limiting on the screens as well as blocking the amplifier's grid bias voltage while configuring the EL84 in a Class-A, self-adjusting cathode-bias circuit. In other words, there are no adjustments to make and no modifications necessary, you simply plug the Yellow Jackets® into the amp's output tube sockets, (in cathode-bias amplifiers) screw the ground wires under one of the output tube socket mounting screws, plug the provided EL84s into the Yellow Jackets® converters, turn on the amp and play.
Yellow Jackets® converters allow you to harness the musicality of EL84 vacuum tubes in amps that don't use them already - it's like getting a whole new amplifier! In place of a 6V6 a Yellow Jackets® converter will even out the tone and make it sound stronger. In larger amps that use two 6L6, 6550, 7027 or EL34 power tubes the Yellow Jackets® converter will drop the output power to about 15 to 20 watts, giving it more of a vintage VOX AC30 sound. In amps that take four power tubes the Yellow Jackets® converter will sweeten the tone and make it more dynamic. There is no rebiasing involved, which makes modifying your amp's tone very easy.
Yellow Jackets® converters give you simple Class-A operation from any amp. They not only rearrange the pin locations of the tubes, but also provide the necessary plate voltage drop and current limiting on the screens as well as blocking the amplifier's grid bias voltage while configuring the EL84 in a Class-A, self-adjusting cathode-bias circuit. In other words, there are no adjustments to make and no modifications necessary, you simply plug the Yellow Jackets® into the amp's output tube sockets, (in cathode-bias amplifiers) screw the ground wires under one of the output tube socket mounting screws, plug the provided EL84s into the Yellow Jackets® converters, turn on the amp and play.
The next best thing to getting yourself a new amp.
How will they change my amplifier?
It's like getting a whole new amplifier! In Champ and Deluxe type amplifiers, the Yellow Jackets® converter output is smooth, strong and more even than with the stock 6V6s. When the Yellow Jackets® 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 Jackets® converters are used in a Marshall® 50 watt or similar amplifier, the overall power drops to about 20 watts 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® converters. In a 100 watt amp like a Twin Reverb or Marshall® 100, either two or four Yellow Jackets® converters can be used. If only two are used and the other two inside or outside sockets are left empty (see Using Yellow Jackets® in 4 tube amps), the output is dropped to about 20 watts. With four in place, the amp puts out about 40 watts and takes on a whole new warmth and richness. A further option in a 4-tube amplifier is to leave two of the original tubes in place and replace the other two with Yellow Jackets® converters. This gives a combination of class-A and Class-AB operation and sounds quite sweet and complex. In the cases of the YJ7591 converters, the overall output power remains the same, but the sound becomes fuller and the rare 7591 are replaced with common and inexpensive EL84 tubes. In old Ampeg Reverb Rockets and the like, you experience a warmth and sweetness that you could never get with the now rare 7591 tubes.
Will they hurt my amp?
No! Yellow Jackets® converters are safe for all amplifiers and transformers. As all Yellow Jackets® converters internally limit voltage and current they put no extra strain on amplifiers' power and output transformers or internal components. Using the Yellow Jackets® converters in higher powered amplifiers actually reduces the strain on the transformers and internal components, as it reduces the overall wattage of the system. Furthermore, the heater (or filament) current of the EL84 is lower than that of the 6L6, EL34 or 7591, so the Yellow Jackets® converters will reduce the strain on the filament windings of the power transformer as well.
How do I get one?
First, determine the type of power tubes your amp uses (contact us or the amp's manufacturer if you're not sure). Next, call your local music store. If they are out of stock, contact us at info@yellowjacketstc.com and we will be able to point you to a Yellow Jackets® resaler in your area. We will be happy to answer any questions you might have on any of our products.
Click here for more detailed information on Yellow Jackets® including schematics, diagrams, pin-outs and more!
It's like getting a whole new amplifier! In Champ and Deluxe type amplifiers, the Yellow Jackets® converter output is smooth, strong and more even than with the stock 6V6s. When the Yellow Jackets® 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 Jackets® converters are used in a Marshall® 50 watt or similar amplifier, the overall power drops to about 20 watts 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® converters. In a 100 watt amp like a Twin Reverb or Marshall® 100, either two or four Yellow Jackets® converters can be used. If only two are used and the other two inside or outside sockets are left empty (see Using Yellow Jackets® in 4 tube amps), the output is dropped to about 20 watts. With four in place, the amp puts out about 40 watts and takes on a whole new warmth and richness. A further option in a 4-tube amplifier is to leave two of the original tubes in place and replace the other two with Yellow Jackets® converters. This gives a combination of class-A and Class-AB operation and sounds quite sweet and complex. In the cases of the YJ7591 converters, the overall output power remains the same, but the sound becomes fuller and the rare 7591 are replaced with common and inexpensive EL84 tubes. In old Ampeg Reverb Rockets and the like, you experience a warmth and sweetness that you could never get with the now rare 7591 tubes.
Will they hurt my amp?
No! Yellow Jackets® converters are safe for all amplifiers and transformers. As all Yellow Jackets® converters internally limit voltage and current they put no extra strain on amplifiers' power and output transformers or internal components. Using the Yellow Jackets® converters in higher powered amplifiers actually reduces the strain on the transformers and internal components, as it reduces the overall wattage of the system. Furthermore, the heater (or filament) current of the EL84 is lower than that of the 6L6, EL34 or 7591, so the Yellow Jackets® converters will reduce the strain on the filament windings of the power transformer as well.
How do I get one?
First, determine the type of power tubes your amp uses (contact us or the amp's manufacturer if you're not sure). Next, call your local music store. If they are out of stock, contact us at info@yellowjacketstc.com and we will be able to point you to a Yellow Jackets® resaler in your area. We will be happy to answer any questions you might have on any of our products.
Click here for more detailed information on Yellow Jackets® including schematics, diagrams, pin-outs and more!
Click below to view details about each type of Yellow Jackets®
How do I know which Yellow Jacket® converter to pick?
If you are in doubt, you may e-mail info@yellowjacketstc.com and we will help you decide.
YJS
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.
YJC
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.
YJ20
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.
YJUNI
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.
YJ7591
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.
YJS
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.
YJC
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.
YJ20
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.
YJUNI
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.
YJ7591
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:
Most guitar amp power tubes are pentodes, meaning they have five electrodes:
- cathode
- control grid
- screen grid
- suppressor grid (or beam confining electrode)
- plate
- cathode
- control grid
- plate
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® adaptor 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.
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.
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® adaptors?
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® adaptors?
No. The Yellow Jackets® adaptors 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® adaptors?
No. We do not recommend using Yellow Jackets® adaptors 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® adaptor internal cathode bias circuit.
- Converts most audio amplifiers with 6V6s and similar-based tubes to EL84s without modification or rebiasing
- One year limited warranty on converter.
- Safe for all common amplifiers and transformers.
Click to order: Standard Version, Triode Version
| Standard Version | Triode Version | |
|---|---|---|
| Converts: | Class AB to Class A operation | Class AB Pentode to Class A Triode |
| Drops Output Power: | Does not drop power | 50% |
| Product Manual |  YJ20 Product Manual | YJ20 Triode Product Manual |
| Additional Documents: | Technical Specifications (PDF), Product Dimensions (PDF) | |
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- Converts most audio amplifiers with 7591s to EL84s without modification or rebiasing.
- One year limited warranty on converter.
- Safe for all common amplifiers and transformers.
Click to order: Standard Version, Triode Version
| Standard Version | Triode Version | |
|---|---|---|
| Converts: | Class AB to Class A operation | Class AB Pentode to Class A Triode |
| Drops Output Power: | Slightly | 50% |
| Product Manual | YJ7591 Product Manual | YJ7591 Triode Product Manual |
| Additional Documents: | Technical Specifications (PDF), Product Dimensions (PDF) | |
If you are having trouble opening PDF documents, visit adobe.com for a free copy of Adobe® Reader.
- Converts most audio amplifiers with 6L6s, EL34s, 6550s or 6V6s to EL84s without modification or rebiasing.
- One year limited warranty on converter.
- Safe for all common amplifiers and transformers.
- Connects to chassis-ground for cathode-biased amps.
Click to order: Standard Version, Triode Version
| Standard Version | Triode Version | |
|---|---|---|
| Converts: | Class AB to Class A operation | Class AB Pentode to Class A Triode |
| Drops Output Power: | 50% to 70% | 70% to 90% |
| Product Manual | YJC Product Manual | YJC Triode Product Manual |
| Additional Documents: | Technical Specifications (PDF), Product Dimensions (PDF) | |
If you are having trouble opening PDF documents, visit adobe.com for a free copy of Adobe® Reader.
- Converts most audio amplifiers with 6L6s, EL34s, 6550s or 6V6s to EL84s without modification or rebiasing.
- One year limited warranty on converter.
- Safe for all common amplifiers and transformers.
Click to order: Standard Version, Triode Version
| Standard Version | Triode Version | |
|---|---|---|
| Converts: | Class AB to Class A operation | Class AB Pentode to Class A Triode |
| Drops Output Power: | 50% to 70% | 70% to 90% |
| Product Manual | YJS Product Manual | YJS Triode Product Manual |
| Additional Documents: | Technical Specifications (PDF), Product Dimensions (PDF) | |
If you are having trouble opening PDF documents, visit adobe.com for a free copy of Adobe® Reader.
- Converts most audio amplifiers with 6L6s, EL34s, 6550s or 6V6s to EL84s without modification or rebiasing.
- One year limited warranty on converter.
- Safe for all common amplifiers and transformers.
- Short enough to fit in most Blackface FenderŪ heads
Click to order: Standard Version, Triode Version
| Standard Version | Triode Version | |
|---|---|---|
| Converts: | Class AB to Class A operation | Class AB Pentode to Class A Triode |
| Drops Output Power: | 50% to 70% | 70% to 90% |
| Product Manual | YJShort Product Manual | YJShort Triode Product Manual |
| Additional Documents: | Technical Specifications (PDF), Product Dimensions (PDF) | |
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- Converts pin configuration from 9-pin to 8-pin to allow certain 6V6, 6K6 and similar low-voltage circuits to use EL84 tubes.
- One year limited warranty on converter.
- Safe for all common amplifiers and transformers.
- Great for adapting tube-testers to test EL84 tubes.
- Perfect for THD UniValve, BiValve-30 and Flexi-50 amplifiers.
Click to order: Standard Version, Triode Version
| Standard Version | Triode Version | |
|---|---|---|
| Converts: | Pin configuration from 9-pin to 8-pin | Pin configuration from 9-pin to 8-pin |
| Drops Output Power: | Does not drop power | to 2 Watts (in UniValve) |
| Product Manual | YJUni Product Manual | YJUni Triode Product Manual |
| Additional Documents: | Technical Specifications (PDF), Product Dimensions (PDF) | |
If you are having trouble opening PDF documents, visit adobe.com for a free copy of Adobe® Reader.
- Converts most audio amplifiers which use a vacuum tube rectifier 5AR4, 5U4 or 5Y3 to a solid state device.
- One year limited warranty on converter.
- Safe for all common amplifiers and transformers.
Click to order: Standard Version
| Standard Version | ||
|---|---|---|
| Drops Output Power: | Does not drop power | |
| Product Manual | YJR Product Manual | |
| Additional Documents: | Technical Specifications (PDF), Product Dimensions (PDF) | |
If you are having trouble opening PDF documents, visit adobe.com for a free copy of Adobe® Reader.
Guitar Buyer Magazine
"The sound reminds me of a cranked AC30, with lots of highs that make a Strat really jangle - you can get a great Rory Gallagher Tone"
Read the Full Article here
Read the Full Article here
Guitar World Magazine
... the next best thing to getting yourself a new amp.
"We tried the Yellow Jackets ina 100-watt Marshall Plexi reissue. Because four EL84s provide about 50 watts of output, the amp wasn't quite as loud. The treble response was enhanced, the midrange somewhat thicker, and the amp produced rich, glassy distortion and sparkling clean tones similar to that of a Vox AC30. The Yellow Jackets transformed the Marshall into a totally different amp. Best of all, it took less than five minutes to install the adapters.
THD's Yellow Jackets are the next best thing to getting yourself a new amp. Costing about the same as a good preamp or distortion pedal, they're the way to go if you want to explore new tones on a budget."
THD's Yellow Jackets are the next best thing to getting yourself a new amp. Costing about the same as a good preamp or distortion pedal, they're the way to go if you want to explore new tones on a budget."
Vintage Guitar Magazine
... too hip!
"THD Electronics, Seattle, has a device called the Yellow Jacket, which enables you to switch the output tube of your amplifier by using an external socket adapter that plugs into an amp's existing tube socket. These adapters come in several versions; they essentially allow you to use EL-84 output tubes in place of 6V6s, 6L6s, EL-34s and the extinct 7591 vintage Ampeg Tube. No re-biasing is required because it automatically makes your amp go into simple Class 'A' operation. It's especially nifty if you can't find good (or the correct type) tubes for your current amp, or if you simply want to change its sound. Tube included - too hip! You can also use two of these things and leave the stock tubes in two of the amp's own sockets (in a 100-watt Marshall, for example), giving you a combination of both Class 'A' and Class 'AB.'"
Guitar Player Magazine
... increase amplifier flexibility
"THD's Yellow Jacket converters increase amplifier flexibility by allowing you to run EL84/6BQ5 output tubes in any amp that normally uses 6V6s, 6L6s, EL34s or 7591s. They simply pop into the tube sockets, instantly reconfiguring the EL84s to Class A self-adjusting cathode bias. An EL84 is included with each converter."
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