Tube Amps / Music Electronics
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|4/29/1997 1:18 PM|
||Is my jcm900 an all tube amp??|
I've heard its a hybrid and thats why it gets good
distortion at low volume?? I need an amp with smooth distortion
and the 900 is really spikey,,, what marshall should i look for?
I mean which marshall rock amps are still all tube that i can find
fairly easily.. ??
|4/29/1997 4:30 PM|
The JCM900 use solid-state circuitry to do alot of the overdrive and switching.
The JCM800 and JMP heads are all tube designs. A JCM800 can be a good choice with either a mod or a good overdrive pedal added.
|4/29/1997 11:38 PM|
The JCM900 Master Vol head uses some diodes as protective circuitry in the preamp. The effects loop is solid state. But the tone you hear is 100% tube. Preamp, inverter tone control and driver.
The JCM900 Duel Reverb head uses some diode clipping in the preamp circuit and IMHO sounds thin and rhaspy.
The Marshall amp I would buy if I wanted pure tube tone and a good range of vintage and modern sounds would be the Plexi reissue. I think it is now called the SLP reissue. I own a Plexi reissue and after adding a standard factory type master volume it is my favorite amp. I jumper the normal and bright inputs for most tones and use a Boss GE7 eq pushed up in the mids as an overdrive pedal. I have been frequently accused of perfect tone. I got mine used for $600.00 and added the master vol myself.
I own two JMPs and I love the tone, but JMPs can sound very different amp to amp so its a "good one" or "bad one" thing. And I like the tone of my Plexi alot better. Good hunting.
|5/15/1997 12:48 AM|
|Mr. Marshall Expert matricciani|
Here is the scoop:
The early Models 1959/1987 which are not the yeras
but the models are all tube..This is the Plexi
design..the non-master volume. They also use a
cathode follower tone circuit..The last tube before the tone circuits is configured as a
cuurent boost, not a voltage boost.The equiv is
an emmitter follower in transistors.
The Master volumes models used a diode for asymetric clipping, because so many players
were using Tube Screamers and Boss Pedals in front
of the amp anyway.
The Silver Anniversary used the same trick with
also a non-cathode follower tone circuit. It
also used the diodes in a different design topology.
The 2210/2205 Channel switching Marshalls used
diode clippers and yet another non-cathode follower tone circuit...The 2210 is my favorite
The JCM900s used less tubes as OPAMP were used to
boost the guitar signal before the tube. The 2210
did this with all tubes. (5 12AX7s vs. 3 12AX7s in the dual reverb model). The JCM 900 line also
went back to the cathode follower tone circuit.
The output transformer was also redesigned on the
JCM900 models since lots of Marshalls were cashing
them in. The 2210 transformer actually comes to
life at medium to high volumes, whereas the JCM900
output transformers sound the same at any volume.
The 30TH anniversary Marshall went back to all tube...no diode clippers. They also designed
channel two around the Plexi 1959 model (mode a)
2204/2205 early master volume non-channel switchers (mode b) and ultra high gain (mode c).
Channel three also has a totally new topography
with 7 gain stages, three of which are cathode
followers. All three channels have cathode follower tone circuits.
I own a Silver Anniversary, 2210 and 30TH anniversary Marshall. They all sound totally
different. I also would not worry about diodes
and op amps. Marshall only puts them in to better
the sound..My 2210 IMHO smokes any Marshall and it
has diode clippers. I have also heard some good
sounding JCM900 amps, all of which use OP amps to
boost the signal but not to create the distortion.
By the way....I also own Boogies, Soldanos, Riveras and a 5150. Each amp has its own voicing
and this gives me many guitar sounds. The problem
with one guitar tone is that it limits you.
|5/15/1997 12:28 PM|
hi Guy. i have a 50w chanel switching 800 combo with rev and 1-12 70w celestion (2210 i think). this amp has the 5 12ax7 that you spoke of. do you know what tubes are for rev, splitter, etc? i run it with 6550's and 4 telefunken 1 sovteck 12ax7's. do you have advice on what spots are best for the better tubes. btw this amp sounds fantastic clean and dist with a les paul. also do you know how to tell the mfg date?
|5/15/1997 1:06 PM|
The american versions came with 6550 tubes
up untill about 1990. You can covert those
to EL-34s if you want. Aspen Pittman has the mod
in his Book.
I will refer to the 5 preamp tubes as V1-V5.
Each 12Ax7 has two triodes.
V3b- reverb send
V4b- reverb return and effects send
V4a- effects return
V5- phase inverter
Lead channel V1a, V1b, V3a
Clean channel V1a, V2a, V2b
There is a diode clipper between V1b and V3a on
the lead channel.
So, you can try tube substitution depending on
what channel you wish to affect.
Reguarding 6550 vs. El-34s.....Its up to
you. I think Marshalls sound better with
EL-34s, but if you like the sound...don't
Also, the combos are a bit bright. The amp
would sound much better played into a closed back
cabinet. A warmer speaker such as a Celestion
Vintage 30, or Celestion Rivera 85 might tame
down the highs in the combo configuration.
As far as 12Ax7 differences, your not going to
hear much change..I've tried all kinds. What will
change the sound is converting the amp to EL-34
power tubes. I've nevr heard a 6550 equipped
Marshall, so I'm not one to tell you whether the
EL-34s will sound warmer.
A cool setting at low volumes is this:
Turn the presense up to add the highs lost from
the low treble setting. The reverb will also
Incidentally, on the 2210/2205 preamps, the volume
for the lead channel acts like a gain..You need
volume on 10 and gain on 10 to get max gain.
This is because the volume pot drives V3a.
Hope this helps Ryan.
|5/15/1997 2:29 PM|
hi Guy. i would like to try svetlana el34's but i dont have the book. i hear the 6550 doesnt clip hardly at all. do you know the conversion for 6550 to el34? by the way i run the clean ch at: v=5, t=4 b=7 dist: pre=10, v=6, t=0, m=5, b=10 master~6, rev~4 i have no presence. the tone changed a lot going from the sovtek to the telefunken pre tubes, more head room (no dist on clean) fuller more dynamic everything. i cant run the dist vol at 10 because i switch from clean to dist alot and i need the volumes to match. the dist is more than whats associated with a blues sound, but less than the saturated "cranked marshall" sound where power. do you know the layout of the tubes corresponding to the "v" system? from the power tubes there are 2 tubes to the right and then 3 tubes offset back.
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