Load Boxes and Pulling Twin Power Tubes
ASK AMP MAN
JEFF BOBER
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
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.
Also, as a follow up, I received this from a
reader regarding a column I wrote a couple
of months ago [Feb., 2010]:
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
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
Yes, you can physically remove output
tubes from the Twin, but you must remove
two, not one.
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
and resistor all in parallel: tip connections of
both jacks to one end of the resistor, sleeve
connections of both jacks to the other resis-
tor 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 your-
self 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 ampli-
fier” 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 cir-
cuitry, but since the load box is already pretty
basic, I don’t know that you will achieve satis-
factory 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.
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.
