TWEAKING A CRATE V33 BY JEFF BOBER
Hello Jeff,
Thanks for all the useful information each
month. I’m hoping you may have some insight
that would help me. I have Crate V33 2x12
combo—a 33-watt, class A amp running EL84
power tubes. It’s not a bad little amp—especially
considering the deal I got on it. But I am looking to turn it into a more powerful little tone
machine. I have swapped the preamp tubes
from the three stock 12AX7s that came in it to
a 5751 in the V1 position, an EF86 in V2, and
a 12AU7 in V3. I also pulled two of the EL84
power tubes, so it is running at 18 watts. This
allows me to drive the power section harder
and that contributes more to the tone.
Next I plan to change the stock speakers to
a couple of Warehouse Guitar Speaker models. The amp is currently looking for an 8 Ω
load. Would you suggest I get two 8 Ω models
and run them in series in order to run the
power section even harder? I’m also wondering if you could give me a few mods to make
the tone stack more effective. In particular,
there doesn’t seem to be much response coming from the mid control. I am looking to
enhance the “British” feel, which this amp
already has.
Thanks for the suggestions.
—Bryan
Hi Bryan,
As far as your V2 selection
of an EF86, I’m sorry but this
tube will simply not function in
this amp. The stock tube for this
position is a 12AX7, which is a
dual triode. An EF86 is a pentode style tube and has a completely different pin out configuration that will simply not work
if installed in this socket. Besides
that, even if you were to rewire
the socket to accept this style
tube (which is not an easy task
in an amp with circuit board-mounted sockets), you would
be losing an entire gain stage,
since the triode has two but the
pentode only has one. This tube
serves as a sort of mixer for the
clean and dirty channels, as well
as a tone stack driver. While
these functions could possibly
be accomplished by one gain
stage with some modification,
I would recommend against it.
If you wish to experiment with
alternate tubes in this position,
a 12AT7, 12AU7, ECC832, or
823 would work.
With respect to the V3 posi-
tion, you mentioned you installed
a 12AU7. That tube will certainly
function in this position, but
being it is the lowest gain of all
styles of tubes that will work here,
you will have the most reduced
signal level driving the output
stage. This would translate into
more signal level required from
prior gain stages in order to drive
the output tubes to the same
level. Not a bad thing at all, but
just know that it definitely chang-
es the feel and touch sensitivity
of the amp. This, of course, is all
personal taste, so experiment with
a 12AX7, 12AT7, and 12AU7
in this position, but steer clear
of the ECC832 and 823 here.
The two different triode sections
would substantially unbalance the
output stage making for an asym-
metrical output, which is not very
good for quality clean tones.
JEFF BOBER, one of
the godfathers of the
low-wattage amp revolution, co-founded and was
the principal designer
for Budda Amplification.
Jeff launched EAST
Amplification in 2010, and he can be
reached at pgampman@gmail.com.
