I used to own a Boogie MKIIa –
it was great at what it does but
pretty much a one trick pony. I sold the boogie when the blue grilled
Vox
Valvetronix AD60VTH modelling head was more to my liking,
especially with the 2x12 celestion alnico loaded Vox cabinet that I
bought from Northcoast
Music. Years later I found this
slightly battered Selmer Truvoice Zodiac Twin Thirty "croc-skin" combo
amp in a
local store. They had no idea what it was.
To be fair I had no idea what it was either, and it didn't help that it
was missing the original front panel. This is what it
was SUPPOSED to look like:
Damn, I'm missing that way-cool german gothic badge letters. Note
the difference in the letters on the image on the right - I'd LOVE to
find those.
Only the rear panel badge betrayed its
origin:
I wasn't familiar with vintage amps
beyond fenders, marshalls, and voxes. When I got home and checked my
books and the net, I decided to go back and check it out. Knowing
it was similar to Vox amps, I brought my strat to audition
it. When I returned to the store, closer inspection revealed it
was indeed the
“croc-skin” amp from 1963-1965 and it was the most desireable Selmer
model on the vintage market - the 30w Twin Thirty "croc-skin" with
celestion alnico
speakers. I already had the Valvetronix which
offered a lot of amp, so this Selmer had to be unique enough to justify
taking it home. You gotta be careful of old tube amps though –
they can be a
maintenance headache and the older the amp the more likely it will need
an overhaul. This thing is over forty years old and way past its
expiration date. There is a risk of
replacing failing components like leaking capacitors, worn tubes, or
burned out
transformers - potentially expensive repairs.
So in the best beach blonde delivery: what
does the Selmer have that a
modeller doesn’t? I’ve had flight time with vintage
british valve
amps and I know what they sound like. Vox AC30, AC15, plexi
marshalls, and sound city. I’ve even heard some tweed fenders.
The Valvetronix can deliver all of those. But the Valvetronix cannot
deliver the crispy juicy jangle of this Selmer amp, especially on
single coil guitars. This 30w combo has a nice high end that
doesn’t pierce the ears or is overbearing. It's sort of like
hearing a Fender tweed with the pillows removed from your ears. I
really like the
variations in tone between the “Selectortone” and the various pickups
on my strat. My attempts to emulate the Selmer with the
Valvetronix were futile, could not even get close - even though both
amps had the same celestion alnico speakers. Even though it is a
30w amp, it is deceptively LOUD
(aided by the excellent SPL of the alnico speakers).
You can get some really sweet blues or funk stuff dripping out of this
thing although it is reluctant to overdriving. It's the only amp
I've heard that can make my Les Paul approximate the twang of a strat
(very few amps can do that). This is not an amp to reach for
creamy sustained
distortion but if you slam a Gibson hard enough it starts to sound like
early AC/DC (listen close to AC/DC and you will hear minimal overdrive
– the unique crunch of the Young brothers comes from their hard
strumming technique). It’s got the spank of a fender tweed or
blackface, the jangle of a Vox, with the raw sting and bite of a
Marshall power tube amp. Interesting combination of tones and it
responds quite well to dynamics of playing whether you feather the
strings, flatpick, or slam them.
These Selmer amps are underrated and relatively unknown, especially in
the US where there was no distribution of any kind. Back in the
day, you had to travel to England to buy a Selmer then bring it back to
the US. And back in the "croc-skin" days there was no AC mains
selector for US110VAC, you had to retrofit a step-up transformer
($$$)! My amp already had the step-up transformer intact,
there's a hole in the back panel to accomodate it. Selmer
was making guitar amplifiers starting in the late
40s, well before the first Vox amps in the late 50s. They were
the most popular guitar amp in the UK and Europe until Vox
out-manuevered them with their savvy marketing and group
endorsements. Selmer did defend their second place throughout the
sixties and their most famous endorsers were Gerry And The Pacemakers
with their "wall of Selmers", croc-skins no less! But Marshall
and Hiwatt squeezed them out of the market by the 70s.
The Twin Thirty has two channels
– channel one possesses a volume
and tone control (no separate bass/treble) and is slightly hotter and
fuller than channel two. Channel two has identical controls in
addition to the “Selectortone” and the tremolo. The
“Selectortone” is a basically a tank RLC circuit with varying RC
components switched in and out via a pushbutton piston switch panel not
unlike the AM radios on old cars of the same era. An RLC circuit
is a notch filter and can cut only, no boost - the opposite of the
bandpass action of a wah-wah pedal. The result is
tones unlike anything you’ll get out of standard “tone stacks” in
typical guitar amps, and they’re especially effective with a single
coil guitar like a strat. Buttons are marked low bass, bass,
medium, treble, high treble, and rotary control which makes the tone
control effective. The tone control attenuates the high
frequencies.
The tremolo was well designed
and sounded very effective. Selmer used a unique visual indicator
in the form of a tube that emitted a blue-green glow. This tube
was
fitted to the front panel between the speakers and was visible through
a bezel in the grillcloth.
This was called the
“blinking eye” in which the tube flashed in synchrony to the tremolo
rate so you had a visual indicator of tremolo! But be sure the
RCA plug on your footswitch has a secure connection or the tremolo
won't work - that's what was wrong with my amp.
The “croc-skin” is a highly striking visual feature – a two tone tolex
style of black and facsimile crocodile
scales.
“Croc-skin” was the british fashion rage during the early
60s. Although there are some slight cigarette burns on the top of
the amp, the tolex has no tears and is in fine condition. When
Vox and Marshall popularized the all black tolex, these “croc-skin”
patterns quickly became old hat, which is why they were made only for
two years. Today they are desirable in vintage amp circles
although not well known and highly underrated. Selmer never had
US distribution for these amps so examples in the US are rare,
especially the old “croc-skin” line (I don’t recall “croc-skin” being a
fashion style in the US).
This amp has the original Celestion alnico
speakers
which sound excellent – they are identical to the
Celestion “alnico blues” installed in Vox amps with the exception of
the magnet cover, which has zero bearing on the sound. The
speaker is supposed to have a datecode that can be used to date the amp
but there IS no datecode on them (my amp tech couldn't fine them
either). My serial number is 13xxx which is
lower than a 1964 specimen at serial #16723 so it is likely I have a
1963 model, the first year they made them. However a forumite did
note that my specimen has grey handles
instead of black.
The
tolex style that preceded the "croc-skin" was a two tone blue-grey -
Selmer made the Twin Thirty in this style and as you can see from this
early
blue-grey
specimen it has the same grey handles as my amp. So I
probably have a transitional specimen - "new" croc-skin tolex with
"old"
grey handles and a serial number landing it in its first year of
production. Whoa!
Unfortunately it doesn’t have the original grillcloth and
it is missing the “blinking eye” bezel and large german gothic “Selmer”
letters on the front. As far as I could ascertain there were no
sonic indications of failing leaking caps and the chassis and metal
components were free of rust. It just came back from a vintage
amp tech and he did very little to it - all the tubes, sockets, caps,
everything was in good condition. He was amazed it was this good
for the miles it had on it.
The grillcloth not being original and absolutely no luck at locating
replacement grillcloth that is an exact replica of the original, I
decided that ugly grillcloth had to go. So upon unceremoniously
tearing off the grillcloth, I was greeted with a surprise. There are no holes in the speaker panel
for the SELMER badges! The holes that are in a typical
Twin-Thirty speaker panel are NOT in my specimen. After some
research I found a
catalog entry for this amp and this
is what the amp may had looked
like. There are some holes on the bottom of the panel from wood
screws so this may have had the separate panel with the badge letters
on it.
The speaker panel had been secured with four woodscrews, one on each
corner. The factory arrangement was three per side. The
original holes were still there so I replaced the wood screws with
T-nuts and long screws. Believe it or not, this does impact the
tone. I also replaced the bolts/nuts securing the speakers as
some were missing and the threads are non-standard - neither standard
or metric would fit them. They were rusty so they were replaced
with T-nuts and bolts.
I spent six months prowling ebay.co.uk for an empty cabinet to scavenge
grillcloth and badge letters from. Two came up, but the buyers
did not want to ship to the states. I gave up looking for
one. Since no original grillcloth was available, I opted for
speaker grills. I decided that a set of gold-finished speaker
grills would look good on this. Gibson has them on their amps but
I cannot find the grills separately anywhere. So I simply bought
black speaker grills and a can of gold paint from the hardware
store. Some quick painting and they were done. As you can
see from the pics at the top of this page, I think it looks better than
as purchased (I sure would like it restored to original).
Asking price? Very reasonable compared to market prices.
The vintage Celestion alnico speakers alone were worth what I paid for
it.
These amps are so rare in the US that this one has a step-up
transformer to UK220VAC since the mains
selector has no position for
US110VAC. I thought I would re-sell it for a
profit, but the more I play it the more I'm leaning towards keeping it.
I would like to restore it to stock, but the grillcloth, large german
gothic badge letters, and “blinking eye” bezel are serious
unobtanium. The best source is ebay UK, since Selmer amps were
more prevalent in the UK. It’s a good thing the “croc-skin” tolex
is in good condition because no one makes anything like it today.
An inspection of the schematic reveals a remarkably simple amp.
Tube arrangement is 3xECC83 (12AX7), 2xEF86, 2xEL34, and tube rectifier
(UK 50hz=GZ34 or 5AR4, US 60hz=GZ32 or 5U4). What was surprising
was how
quiet this amp is. Little if any noise or hum can be heard, even
with the single coil pickups under fluorescent lights. There’s a
reason for this, which I’ll explain below.
The Selmer Truvoice Zodiac Twin Thirty is an interesting amplifier
design.
The power amp is a class A/B with negative feedback,
similar to the Marshall JTM45 design. In fact the output
transformer is the same as the one used in the JTM45. The preamp
is totally unique
though, and this is where it gets interesting. The ECC83 is the
input gain stage while the EF86 is the
gain recovery stage after the tone filters (the Twin Thirty has only a
single "tone" control so no "tone stack" with separate bass/treble
controls). Each channel has
independent ECC83/EF86 sets. Gain recovery stages after the tone
filters were usually reserved for the high end amplifiers in a product
line. Instead of diming the ECC83
to full gain at the input stage like most guitar amps, the gain in the
Selmer Twin Thirty is divided between the ECC83 and the EF86.
This exploits the optimum features of both tubes.
All active components – tubes, transistors, opamps - have a parameter
called gain-bandwidth product.
The gain is inversely proportional
to the bandwidth meaning as gain increases the bandwidth decreases
(high frequency response is sacrificed for gain). Gain-bandwidth
product is also dependent on the device’s parasitic capacitance, which
exists in any active component. The lower the capacitance, the
better the bandwidth. Parasitic capacitance is a product of the
internal components of the device during the fabrication process and it
cannot be reduced or eliminated.
The ECC83 is optimal for the color it imparts on guitar signals but its
inherent parasitic capacitance limits its high frequency
performance. That is why an ECC83 tube has a brighter clean
tone than an overdriven tone – with the ECC83 pushed into heavy metal
overdrive, you’re compromising high frequencies. You’re adding
ear-pleasing even ordered harmonics at the expense of high frequencies.
EF86s are optimal in that they have higher gain, lower noise, and lower
parasitic capacitance than the ECC83 and were popular as input stages
for the microscopic signals from vinyl record needles in hi-fi stereo
systems. They are very clean pristine audio tubes at high
gain. But they impart little harmonic color and tend to sound
“sterile” with guitars (precisely why they are ideal for phono
records). EF86s also are notorious for being microphonic and when
operating in high gain they tend to “squeal” in a hostile vibrant
environment like a guitar combo amp.
So the Selmer design exploits the best features of the ECC83 and EF86 –
the ECC83 is the input stage where it imparts its color on the guitar
and the EF86 is post the tone filters where its superior gain-bandwidth
and low noise is exploited. The Twin Thirty divides the gain
between the ECC83 and EF86 – by operating the ECC83 at lower gain and
the EF86 at higher gain, the gain product of both stages is equivalent
to a proper guitar preamp. With the ECC83 operating at less gain
it is capable of better bandwidth (read more high frequencies).
The EF86 breezily passes the same high frequencies. This is why
the Selmer Twin Thirty sounds so crisp and juicy – the high frequencies
of single
coils shines through on this amp like nothing else. This is also
why the Selmer is so quiet – the low noise EF86 carries the bulk of the
amplifying chores. An unfortunate compromise of this design is
lack of sufficient overdrive at the input stage because the ECC83 is
not dimed out like a typical guitar amp.
The Zodiac Twin Fifty - 50w instead of 30w - shares the same preamp but
the power amp is a
different
circuit and the alnico speakers were "upgraded" to Goodmans whose
heavier wattage can better withstand the fifty watt muscle. If
you put two 15 watt celestion alnicos - total 30 watts - in a fifty
watt amplifier, the amp will make quick toast of those valuable
alnicos. The Thunderbird models (adds reverb and
separate bass/treble controls) do not have the same valve arrangement
(no EF86 tubes) so both the preamp and power amp are different.
So the Twin
Thirty is unique in the Selmer line.
This is an amp that is sensitive to technique - baby the strings and
you get that sweet juicy tone of a Vox, then if you slam 'em it will
break up like a Fender Tweed. Nice dynamic tone changes you can
control with your fingers. This is also an amp that will
highlight sloppy picking technique, so I look forward to developing my
playing on this amp. You're not going to get a Selmer Twin
Thirty to distort into creamy overdrive - and these things do not react
well to pedals, a trait shared with most pre-Marshall british
amps. As you approach 10 on the volume knob you can hear the EL34
power
tubes distorting, which tends to be transient distortion and
you won’t get much sustain in this design. Coupled with the
rectifier tube, this transient distortion “sags” which softens the
impact of power tube breakup and imparts a dynamic change in tone on
the transients. This is a very pleasant trait for
blues music.
As per most 1960s british amps, the Selmers do not like most
pedals. My VestaFire RV-2 dual channel spring reverb sounded
great as did my brother's Mesa Boogie V-Twin. But my Vox Tonelab
SE... meh. The clean amp models were good but the dirty amp
models were not pleasant. Yes I did put the line out in AMP
mode. This amp just does not like its preamp signal to be
over-processed.
However I *did* find one very useful pedal - the Morley A-B
footswitch. You can route to either A or B, or to both at the
same time. Since the Selmer was a two channel amp, my experiments
driving BOTH channels were
interesting. The selectortone can get some really tinny sounds
which make you think "where would I use that?!?" Well using the
A/B switch to drive BOTH
channels, the tinny channel combined with the full-ranged channel will
yield a full-range sound with a nice crispy attack. Using
combinations of selectortone this really expands the variety of tones
out of this amp - and it seems quite content to do this, contrasted to
pedals!
Selmer was very wise to have separate chassis for preamp and power
amp. The hum-inducing transformers of the power amp are in a
separate chassis in the bottom of the cabinet, a safe distance away
from the high gain preamp that is sensitive to interference whose
chassis is in the top of the cabinet (back of
amp with panels removed). Very
few guitar amps use this design, unless you are using a modern modular
rack system with separate preamp and power amp units. This is the
primary reason why the Selmer Zodiac Twin Thirty is a very low
noise/low hum amp.
Another advantage to the separate power chassis is improved heat
dissipation. Accumulated heat gradually destroys electronics over
time – caps, tubes, transformers, everything. The hotter the
heat, the faster they break down. With the common knowledge that
heat rises, Selmer put the heat generating components – the power tubes
and transformers - in the bottom of the cabinet where heat has plenty
of room and few obstacles to rise away from the chassis. Today
fans are used to
force cool air on heat generating components – that works great UNTIL
the fan breaks down (fans have a tough life and they don’t last
forever). Selmer chose a passive system that is not vulnerable to
a malfunctioning fan. That also kept the price reasonable by
eliminating the cost of a fan.
So why is that important? A cooler amp is a more reliable
amp. Amplifier heads such as Marshalls have the disadvantage in
that the heat
generating components are in a (almost) closed space – all that heat
has to escape through a small air vent in the top of the head (don’t
block those vents!). Newer head designs have a fully vented front
panel allowing maximum ventilation. Fender and Vox amps have the
heat generating
components mounted underneath the chassis and since heat rises it can’t
effectively escape around the chassis, it has to escape out the back of
the amp (don’t place the amp flush against a wall!). Today
you have to have a spare amp ready if your main amp goes down.
That isn’t a problem with Selmers (unless you neglected replacing the
capacitors past their expiration date).
Whoever designed these amps was one clever and creative engineer.
A shame his name was lost to history...
