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Load Boxes and Pulling Twin Power Tubes

Hi, Jeff.

First off, thanks for your informative article every month, and thanks in advance for whatever help you may be able to provide. I play in a band that plays mostly acoustic-based music. We’re hitting the road next month and I want to be able to lay in some electric guitar timbres, but I don’t want to bring an amp and cab just to hit a few chords on the electric guitar. However, I’m not really satisfied with simply substituting the amp for some sort of simulator (like a POD or SansAmp). I have an Epiphone Valve Jr. head, and I was wondering if there is some way that I can use this amp without a cab; that is, run it into a DI box and into a PA. I know there are some power attenuators that also act as a speaker load, but these are expensive and are functionally excessive for what I’m looking for. As an alternative to using the Epiphone amp, I’ve been looking at things like the Electro-Harmonix 2ube Preamp or the Rock Block by Surprise Sound Lab, but the latter especially is also very expensive. Do you know of any product that is small and inexpensive—a direct-box-sized thing that acts as a speaker load for an amp? And if not, why doesn’t such a thing exist?

Henry Prol
Jersey City, NJ

Hi, Henry.

Thanks for your question and thanks for being a Premier Guitar reader. I understand your concern regarding the substitution of some sort of amp simulator for the real deal. I’ve been in situations like that and I agree— it’s just not the same. Personally, I do like to move a little air, hence I’d opt for at least some sort of small speaker enclosure. But hopefully using an amp such as your Valve Junior with some sort of load will suffice. Since you will be using a full tube amplifier, including its output stage, you may wind up with a true enough sound to satisfy your tone needs, not to mention one that feels right— which is also very important.

Because the output power of your Valve Junior amp is in the 5-watt range, I can see why you’d consider most of the currently available load boxes to be overkill, and I’d have to agree with you. On the other hand, most do provide some sort of compensation in their line outputs making that signal much more useable for recording or front-of-house reproduction. Anyway, to alleviate the cost of purchasing a full-blown attenuator, I suggest the following.

In a small project box, mount an 8-ohm, 20–25 watt resistor (yes, I tend to overbuild everything) and two 1/4" jacks. Wire the jacks and resistor all in parallel: tip connections of both jacks to one end of the resistor, sleeve connections of both jacks to the other resistor connection. You now have a very basic 8-ohm load box to connect to the output of your amplifier. While this box does not take into account the inductive and capacitive load characteristics of a real speaker load like some pricier load boxes, you’ve saved yourself at least a couple hundred bucks. Connect the speaker output of your amplifier to one of the jacks on your load box. Connect the other jack on the box to the “from amplifier” input of a speaker-simulator direct box such as the H&K Red Box or The Junction by Palmer. (You didn’t think you were going to pocket ALL the money you just saved on the load box, did you?) The output of these boxes will provide you with a balanced signal to send to your PA and monitor system. You could also try some less expensive DI boxes that do not contain speaker simulation circuitry, but since the load box is already pretty basic, I don’t know that you will achieve satisfactory results with just a basic DI box. If you have access to a basic DI box however, go ahead and give it a try first. You never know, it may work just fine for your situation. I hope that helps lighten your load on the road.

Also, as a follow up, I received this from a reader regarding a column I wrote a couple of months ago [Feb., 2010]:

I loved your article on the Twin Reverb. One thing you didn’t mention (and maybe there is a good safety reason for that) is removing one of the power tubes! I’ve known countless guitar players over the 40 years I’ve been playing that have used this technique. In fact, I’ve done it myself for a concert I played where the backline was supplied for the bands. If I remember right, remove the first 6L6 and the power is cut in half. I know this works, but the question is “Am I lucky the amp didn’t explode, or is this another option for getting that tone at a lower volume?” Color me curious—and reckless—if I play another gig where the amp is provided and it happens to be the sterile Twin Reverb. Is it safe to pull power tubes?

Phillip


Hi, Phillip.

In reviewing my column, I noticed that while I did address the option of removing tubes from the circuit, I did it electrically with a switch and not the old-fashioned way of simply removing them from their sockets. Yes, you can physically remove output tubes from the Twin, but you must remove two, not one. Removing only one, no matter which, will cause an unbalanced load on the primary side of the output transformer— and this I highly recommend against.


Jeff Bober
Jeff Bober, Godfather of the low wattage amp revolution, co-founded and was the principal designer for Budda Amplification. He can be reached at pgampman@gmail.com.