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THD Triode Yellow Jacket for 6L6/EL34/6550 Amps Single

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The YJS is an adapter that permits the use of an EL84 power tube in place of a 6L6, EL34, or 6550 in grid-bias amps. There are no adjustments to make and no modifications are necessary. You simply plu... Click To Read More About This Product

Available 08-28-2017 You will not be charged until order ships. Email me when this is in stock.

Gear returned in mint condition. If you're looking for a virtually new instrument in possibly less-than-perfect packaging, this is a great value.
  • Includes 45-Day, No-Hassle Returns
  • Includes full manufacturer's warranty
Gear returned in great condition, with only minor signs of use, such as slight scuffs or pick marks. It looks and plays like new and may be considered an equivalent to display units found in retail stores.
  • Includes 45-Day, No-Hassle Returns
  • Includes full manufacturer's warranty
Ship to Store Available in: 3-7 Days (estimated) Salt Lake City, UT (5.9  mi) View More Stores For Availability


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The YJS is an adapter that permits the use of an EL84 power tube in place of a 6L6, EL34, or 6550 in grid-bias amps. There are no adjustments to make and no modifications are necessary. You simply plug the Yellow Jacket into the amp's output tube sockets, plug the provided EL84s into the Yellow Jacket, turn on the amp, and play.

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.

Will they hurt your amp? No! Yellow Jacket converters are safe for all amplifiers and transformers. As all Yellow Jacket converters internally regulates voltage and current they put no extra strain on amplifiers' power and output transformers or internal components. Using the Yellow Jacket in higher powered amplifiers actually reduces the strain on the transformers and internal components because 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 Jacket will reduce the strain on the filament windings of the power transformer as well.


Use an EL84 in place of a 6L6, EL34, or 6550 in grid-bias amps 
Tubes included
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THDYellow Jacket Converters w/EL84 Duet Tubes

(based on 1 review)

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Reviewed by 1 customer

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(11 of 12 customers found this review helpful)


Sweet sound, much more managable volume.

By Aaron

from Napoleon, OH

Comments about THD Yellow Jacket Converters w/EL84 Duet Tubes:

I installed two of these in a Randall MTS RM100 reducing the overall power from 100 watts down to about 20. It was incredibly easy, simply plug and play. They do not even require a re-bias. From the time I opened the package, I was playing within 10 minutes. These made my volume much more manageable. For me, the RM100 was really overkill, but I love everything about it. It sounds and looks killer. The only downside of the amp for me was that the volume was very difficult to manage in the confines of my small playing space. With the Yellow Jackets, it is still loud enough to decimate my neighborhood, knocking children off skateboards and making decent folks run for their lives. The master volume is much less sensitive and affords me the opportunity to dial in exactly the volume I need. I am playing a lot more through my RM100 thanks to these tubes. In closing I will list the pros and cons of these tubes (for those who�ۡ���ve skipped the narrative). Pros: 1) They sound incredible. 2) Very easy to install 3) More manageable volume, but leaves plenty of headroom. 4) Owns noobs and heals the sick. Cons: 1) A tad pricy. 2) I should have bought them sooner. You really can�ۡ���t go wrong with these.

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