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First, obviously, check the speaker. Give the cone a gentle poke to make sure it's firm
and not deteriorating. Turn the amp on and check to make sure there's no orange plate glow
on the power tubes (blue glow is OK). Don't confuse this with the normal orange glow of
the tube's heater filament. Orange glow indicates that the tubes are dangerously
underbiased--this isn't necessarily a failure, but would have to be addressed right away,
as it might burn a tube or transformer quickly. Pull all the tubes and look at the tube
sockets to see if any of them look cracked or burned. You probably won't be able to do
this, but it won't hurt to ask the seller if he'll pull the chassis and let you have a
look around inside. The most obvious thing to check for is burned or cracked resistors.
Again, this wouldn't necessarily indicate a problem with the amp, but rather that the
components are simply worn out.
Check the electrolytic capacitors for "bubbles"
or residue on the ends of the cans--they'll need to be replaced, if so. It's an accepted
fact that electrolytics "die" after years of use and must be replaced. Ask if
the amp's been played regularly, or stored away--ironically, amps that are played
regularly often sound better than those that have been mothballed, because electrolytic
caps need regular "exercise" to keep from drying out. Of course, the big test is
in the sound! When you plug in and turn on, be sure to give enough time for the amp to
warm up (I'd try to play it for at least a half-hour or so). A 60-cycle hum indicates bad
filter capacitors, which will need to be replaced. Listen carefully for crackles and
drop-outs which might indicate bad internal components--often these don't become apparent
until the amp is really warmed up.
Research. Research. Research. When buying guitar amps, use online stores such as this, Wikis, and information site to help you make an informed purchase.
Superleads (Marshall Mk II, heads only):
1959 (100W) and 1987 (50W) are the two different "superlead" models. They
were introduced in 1965 and are still being made as ’69 reissues. Originally made
with KT66 power tubes (1965) but soon they were replaced by EL34s (1966). The superleads
are easy to recognize with their four input-/no master volume-design. The amps feature two
channels (two inputs for each, the inputs are wired so that they can be used to connect
both channels, thus giving you two different sounds in one, and the level of each
controllable with a volume), bright and normal, individual volumes for each channel and a
standard 4-band EQ. The sound is very "rock", and very wanted. With the lack of
a master volume, the amps rely on power tube distortion. This phenomenon comes with a
price, and the price is volume. And when I say volume, I mean volume. A cranked 100 W amp
is VERY LOUD, therefore power attenuators are often used to reduce the level from stupidly
loud to extremely loud.
An original 1965-68 "plexi" (the term "plexi" is used due to the fact
that the amps had gold-painted plexiglas panels during that era) head might not be very
easy to find, and if you find one don’t expect it to be cheap, but superleads were
made both as JMPs (in the 70ies), JCM800s (in the 80ties) and reissues (today) and you
should be able to find one used.
More detailed Plexi information:
Years are 1965 to 1969, later in Europe. Three phases within the Plexi era: (dates are
approximate)
(mid65-66) - block-lettered Marshall logo, JTM45/Mk II front panel legend, aluminum
chassis, KT66/640vA, 3" power transformer, 2" output transformer, no external
filter caps.
(67-mid68) - gold script Marshall logo, reverse JTM front panel legend, steel
chassis, EL34/460vA, 2" or 3" power transformer, 1.75" output transformer,
one external filter cap.
(mid 68-mid 69) - gold script Marshall logo, JMP front panel legend, steel chassis,
EL34/500vA, 2" power transformer, 1.75" output transformer, six external filter
caps.
JMP series (heads and 2x12" combos):
In 1976 Marshall introduced the master volume amps (2203 (100W) and 2204 (50W)). With
the master volume, the amps no longer had to be cranked to distort. However, no tube amp
will sound good at low volumes and these ones are certainly no exceptions. The amps
feature two inputs (high/low), preamp- and master volume controls plus the standard
Marshall 4-band EQ (treble, middle, bass, presence).
The superleads (1959 and 1987) were also made in the JMP series. Identical to the
originals except for the cabinet. All four models (2203, 2204, 1959 and 1987) were also
made as 2x12" combos (2103, 2104, 2159 and 2187). The sound is still classic rock and
with a humbucker-equipped guitar and one of these, you’ll have no problem grinding
like Malcolm.
JCM 800 master volumes:
The JCM 800 master volume heads also have the model numbers 2203 and 2204 but are not identical to the JMPs. These amps have more gain than the JMPs and this is partially due to a solid state clipping-circuit that was added for this sole purpose. Some tube-fanatics consider this to be a work of Satan and refuse to play JCM 800s. Being a work of Satan or not, the Mk II master volumes still provide a sound that lots of people love. The sound is quite dark and barky with an accentuated upper midrange, so if you are looking for the scooped-mid Metallica sound, look elsewhere or buy an EQ and a distortion pedal. These are no-nonsense machines for more classic rock sounds. They can indeed be criticized for having basically just one sound, but what a sound! Lots of people consider that sound to be THE sound...
JCM 800 superleads:
Basically identical to the original superleads but fitted in the modern bold cabinets.
JCM 800 split channels:
Being the first Marshall with channel switching capabilities, the split channel amps (heads: 2205 (50W) and 2210 (100W)) became very popular for their versatility. The clean channel is by no means clean in the real essence of the word, but to the early 80ies Marshall stooges it was something completely new. The overdrive channel sounds a lot like the master volumes’ and is clearly where these amps excel. Also fitted with a reverb (not indiviual for each channel) and an FX loop, the split channels were Marshall’s first hi-tech amps. The split channels are a little harder to find used than the master volumes, but you should be able to find one. It sounds quite like its brother, the master volume, but with some (limited) channel switching capabilities.
General JCM 800 info:
Introduced in 1981 (split channel amps in 1982) and discontinued in 1989. Superleads available as heads only, 50W split channel and master volume amps available as heads, 1x12" and 2x12" combos, while 100W split channel and master volume amps were available as heads and 1x12" combos. Pre-1984 JCM 800s for the American market were shipped with 6550 power tubes and sounds a lot different from the EL34-equipped "standard" ones. Converting an originally 6550-equipped amp to accept EL34s is a minor mod and should cost you more than $50. The 2203 was reissued in 1995 as a special limited edition amp in red tolex, with matching 4x12" cabs.
25/50 silver jubilee series:
Also a split channel amp, introduced in 1987 to celebrate 25 years of Marshall amps and Jim Marshall’s 50 years in the music business. The front panel layout is simpler than the JCM 800 split channels’ with only one gain knob, one "lead master" and one "output master". The gain and the "output master" knobs are push-pull and activates "rhythm clip" and lead channel respectively. The amps were made in silver/gray tolex and also feature a half/full power switch (pentode/triode) and an FX loop but no reverb. Generally considered to be one of the best sounding (Yes, I know that "best" is a relative term...) Marshalls ever, it is a little brighter sounding than the "ooouumphy" JCM 800s but yet not as bright as a JCM 900. These amps will give you a sound that will suit most anywhere in the rock spectrum of music, from Jimi Hendrix and Led Zeppelin to Metallica or even Meshuggah (just buy an EQ...) The jubilee amps have recently become something of a collectible and finding one could require some serious research. The 2555 was reissued in 1996 as the JCM Slash signature amp, with vintage 30s-equipped 4x12" cabs.
JCM 900 master volumes:
The JCM 900 master volume was designed to give the late 80ies metal bands what they
wanted the most, MORE GAIN. And more gain they got. However, the sound of the 900s is not
as ballsy as the 800s’. To get the extra gain, the diode clipping-circuit was
modified which in turn gave not only more gain but also a somewhat buzzier and brighter
distortion.
But the players loved it anyway, and lots of people still do. By backing the gain of you
decrease the amount solid state-clipped signal (the clipping circuit is fed with less
signal the lower the gain is set) and you can get some killer more vintage "true
tubeish" tones out of these amps too. The tones produced by these amps will first and
foremost suit modern thrash metal, hardcore or punk players that don’t need a clean
sound. In 1994 the Mk III was replaced by the Mk IIII, also known as the SLX. These amps
feature an extra ECC83 (12AX7) preamp tube and even more gain than the original JCM 900
master volumes.
JCM900 dual reverbs:
Featuring a clean channel with some real headroom, sounding a lot less
"Marshall" than previous "clean" Marshall-made channels. The overdrive
channel is less buzzy than the JCM 900 master volume and does not have as much gain. Front
panel functions include individual gain controls for each channel, a shared 4-band EQ, and
individual reverb and master volume controls.
Without knowing it, Marshall made (in 1990, when Poison and Warrant were still the big
thing) an amp that suited the next generation of "alternative" bands. When the
gain is set low on the overdrive channel it will sound somewhat "retro" and
turning it up a bit (not past 2:00 with humbuckers, preferably in neck position) results
in a chunky ballsy tone that screams "Tool" or "Soundgarden". Scooping
out the mids and turning everything else up will give you an "almost-SLX" sound,
that can be used for more "metal" applications.
General JCM 900 info:
The Jcm 900s were originally equipped with EL34 power tubes, but from 1994 an onwards
they came with 5881 power tubes due to the fact that, at that time, EL34s were becoming
hard to find. The die-hard Marshall stooges consider this heresy, while others (including
me) think that putting 5881s into the 900s were a not-so-bad move since 5881s made the
900s sound less brittle and a little more ballsy. Anyway, it’s no big deal modding a
5881-equipped amp to accept EL34 tubes.
The master volumes came as 50W heads and 1x12" and 2x12" combos and 100W heads
and 1x12" combos. The dual reverbs came (heads still come...) as heads, 1x12"
and 2x12" combos in both 100W and 50W models. No SLX combos were ever made.
Anniversary series:
The most versatile Marshall to date. 3 completely individual channels, clean, crunch
and lead. Clean is clean, jazzy clean or country clean or pop clean, you decide. Crunch
features three gain modes (A, B and C), A gives you classic superlead crunch, B takes you
into 2203 territory and C gives you the SLX scream, and a little more. The lead channel
continues where the crunch channel stops. Insane amounts of gain, I haven’t heard
more gain coming from an amp, with a possible exception for the JCM 2000. Whatever your
preferences might be, the anniversary series amps has got the sound for you. The design is
also very hi-tech. Channel switching is MIDI-controllable, the FX loop has got individual
levels for each channel and is switchable from serial to parallel, the power amp features
two different damping modes (low and high) and an "auto" option that
automatically assigns the "right" mode for each channel, a recording compensated
balanced XLR output, a low/high switch for pickup compensation and a "low volume
compensation" that fattens the tone up a bit at low volumes. Do you need to hear
more?
The anniversary series amps were introduced in 1992 and the first year the amps were made
in blue tolex. A special (brass-plated chassis, gold logotype) limited edition series amps
were also made in 1992. The series were continued unmodified, but in black tolex, until
late 1994 when the lead channel was redesigned and the amps renamed with an "LM"
after the model number. The LM amps are all fitted with 5881 power tubes as opposed to the
EL34s that the original anniversarys came with.
Proper care of tube amps
Tube amps are generally going to be just as reliable as their solid-state counterparts if you just observe a few things about them:
1. Take a little extra care in transporting them. While you can generally bang around and lightly toss solid-state amps into trunks, back seats of cars, truck beds, etc., with tube amps you have to be a little more careful. What i generally do when transporting tube amps is set aside a special place in the car so that the amp isn't going to be jostled around with hard shocks when i make abrupt movements with the car or hit bumps. Generally this means the back seat or the trunk with some towels or clothing around the amp. When you get to the gig, just make sure that you take special care not to bump the amp into other things, or to just drop the amp on the floor, if you're in the habit of doing that.
2. Make sure that there is proper ventilation for the tubes. Tube amps run hot--especially if they are wired in class A--and they need proper ventilation. Generally this just means that you shouldn't put your polish cloth or set lists over the ventilation holes, and you shouldn't set the amp right against a wall so that there is no air to get to the vents. Some players even keep a fan on the amp, though i don't think this is necessary.
3. Change the power tubes regularly. "Regularly" means a lot of things to a lot of different people. GENERALLY SPEAKING, six months to a year is fine for most power tubes if you're gigging regularly (say, once a week or once every other week) and rehearsing regularly--and this means at typical club volumes. If all you do is play the amp at home at bedroom levels, the tubes can last two years or more. If your amp is bias-adjustable, then you need to make sure that the bias is set when you change power tubes. If your amp is fixed-bias, it's generally a good idea to stick with the same power tubes that came with your amp.
4. Make sure that a speaker is ALWAYS plugged into the amp. Tube amps need to see speakers plugged in at all times, so you cannot run a tube head or tube combo without the speaker plugged in! This is a big mistake and can cost you $200-300 if your amp blows a transformer. Even after you replace the tranny, the amp often sounds different--some describe the amp as being "neutered" after replacing a blown transformer.
5. Make sure that the speakers are plugged in at the proper impedance--or at the very least, a mismatch in the "safe" direction. The best scenario is to match the impedance of the speaker or cabinet with the amp--if your speaker cabinet is 8 ohms, your amp should be set for 8 ohms for best results. If you plug this same 8-ohm cabinet into the 4-ohm setting on your amp, that will also be safe, but you will generally lose about half of your power as a result of the mismatch. If you take this same 8-ohm cabinet and opt for the 16-ohm setting on your amp, you're going to likely blow the head up as it tries to produce twice as much power. again, this can result in a blown transformer and the same neutered tone if you have to replace it.
6. Use the standby switch when powering up and powering down. The standby switch allows the amp to sort of "warm up" and allows the tubes to settle into a sort of equilibrium state before it gets slammed with high voltage. If you generally let the amp warm up or down in standby for about 30 to 60 seconds when powering up or down, you'll find that the tubes last longer.
That's about it, really...taking care of a tube amp is really not as difficult as one might make it out to be. With a little care and some maintenance, the amp is going to sound fantastic for a lifetime!
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