Rickresource Rickenbacker Forum

Hi Greg,

What is the purpose of these units?

Here is a blurb that I ran across:

"THD Electronics Yellow Jacket tube converters. The Yellow Jacket tube converter is a specialized adapter which permits the use of EL84/6BQ5 power tubes in place of 6L6 or EL34 type tubes. Yellow Jacket converters not only re-arrange the pin locations of the tubes but also provide the necessary current limiting on the screens and cathode. Yellow Jackets block the amplifier's grid bias voltage, which configures the EL84/6BQ5 into a class A self adjusting bias circuit.

These Yellow Jacket converters are great for amps including Marshall 50 and 100 watt tube amps, Fender Super Reverb, Deluxe Reverb, Pro Reverb, Twin Reverb, Bassman, Showman, Tweed Pro (5E5-A), Hot Rod Deluxe, Hi-Watt 50 and 100 watt amps, Sound City 50 and 100 watt amps, all Rivera amps, Jim Kelley, Soldano SLO and Hot Rod Series amps, Mesa/Boogie 50 and 100 watt amps, Bogner, VHT, Koch, ect.... "

Correct me if I'm wrong, but they allow you to use lower output power tubes to get more of the amp's tone without subsequent hearing loss!
IE: crank that 50 or 100 watt amp but what you get for output is closer to perhaps a 30 watt amp.
Great sound at a lower volume.
I tried my old 50 watt Bassman head one day at about 7. Great sound, but things started falling off shelves! Not really eardrum friendly!

I have not used them, but I believe it's a little more to them that just lowering the wattage. You are substituting a EL84 power tube for your current power tube so that's going to change the tone of the amp. It also changes the bias of the amp from a fixed bias to a self bias.

They also rearrange the pinout to work with the other tubes, which have a different base (9 vs 8 pin). The EL84 tubes will sound different. Personally, I don't like them that much, the amps I have heard them in are harsh sounding to my ears, at least for clean tones. I much prefer a 6L6.

If you are only looking to lower the output volume, you might want to try a THD Hot Plate, which basically soaks up the power while letting the amp work as if it were playing loud. Same principle as a Power Soak, but with a couple of extra features.

I've had a pair of Yellow Jackets in my Hot Rod Deluxe for a few years now. They do lower the overall volume a little bit, but not as much as you'd think. It can still get pretty loud. On my amp (with 6L6's installed) a setting of 2 would be loud and very clean. Cranked up to 6-7 would be where the amp started to sing, but that was WAY too loud. Especially for home use. Heck, even 2 was bordering on too loud at home. And usually 6-7 was way too loud at gigs.

With the Y-J's, I can crank the amp up to 6-7 in any environment and it sounds pretty good to me.

They do change your tone a bit though. Personally, I like it. Makes it "Vox-y" in some ways. But really, they are something you need to try out with your amp to see if you like them or not. And like Jeff said, another alternative is an attenuator of some kind - Hot Plate, or Weber Mass of some sort. The Webers are a lot more versatile.

Thanks for the info guys. I want to do something to reduce the ear shattering volume that my Twin produces when I want it to give me some nice crunchy tube distortion.

If you know what I mean. I am sure my neighbours do. LOL

I use yellow jackets a lot in my THD univalve, since I really like the sound of EL84 tubes. As was mentioned before, the EL84 operates at about half of the power of an EL34, so it is only 3db down at full volume. You can also use 6V6 tubes in _some_ amps (be very careful about voltages- they can't take as much as most 6L6 tubes). The 6V6 is a bit smoother than an EL84 and most don't have the high end sparkle of a great EL84- I'm slowly warming to 6V6 tubes, though.

While I'm a big fan of THD and their products, I recommend the Weber Mass attenuator slightly over the THD Hot Plate. It uses a speaker motor instead of merely a resistor load and it also allows for different speaker loads.

The yellowjackets are reliable, and will lower the overall volume of your amp and change the tone a bit...whether it is right for you or not you'll have to decide. A Twin Reverb is really the wrong amp to try to get low volume crunch out of, especially if it has the original JBL speakers that some of them came with. Even with yellow jackets it will still be very loud and it won't crunch up a lot. A smaller amp would be a better choice, especially something with less efficient speakers!