Mini JCM800 18 Watt
Based on the 2204

!!!CAUTION: TUBE AMPLIFIERS CONTAIN LETHAL VOLTAGES EVEN WHEN UNPLUGGED!!!

Table of Contents

 
              SAFTY READ FIRST        

 
  New  Mini JCM Amp Kit

  Hear It

  Front Top

  Inside

  Cliff Jack Wiring Detail

  Combo Back Side

  Close up V1

  Close up V4 V5 V6

  Board Installed

 

        Home              



Mini JCM800 MV KIT W/MODS

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I am proud to announce the new “Mini” JCM 800 Master Volume High Gain Amp Kit!

This kit is based on the legendary Marshall JCM800 model 2204 from the ‘80’s. Most Marshalls with that "signature" tone were not stock, so to get your sound in that “Holy Grail” of tone I have added a few mods! This kit has great sustain, and tone that really does rock and to top it off it provides it at bed room levels without any other gadgets, such as tone robbing attenuators or stomp boxes! The sound is heavy but with some nice clarity, and midrange. The tone stack has a more usable range than a stock amp. Note: This amp kit is designed for high gain at low and medium volumes (med. vol.= pretty loud) at these volumes the amp is stable and sounds great as described above, at higher volumes 3/4 and up the amp can become unstable. But usually this is due to a few factors and is just what could happen. This kit is not for a beginner or amatures and It is not intended for your first time diy amp build. Electrical skills, knowledge and safety are all needed to build this kit. You build it at your own risk, and according to your local electrical codes.

Features:
1. Single Channel High Gain
2. 2204 Modded Preamp
3. PPIV MV (drive control)
4. EL84 Power Amp
5. Adjustable Bias
6. Quality Transformers & Choke Made in Canada
7. One chassis styles available, designed for a head but could be fliped for a combo
8. Comes With or Without Tubes
9. Power Switch and GZ34

Sound Samples
This clip was mic directly into my sound card no effects,
volume was on 2, and it was at bed room levels!
The guitar is a LP Deluxe with a single 12" Hellatone 30 speaker,
all traks recorded with the same amp described above.
  Guitars Gone Wild
  Hammer Of the Axe
  Southern Sundown

Includes:
A: Blank 16ga Aluminum Chassis Head or Combo if flipped.
C: Resistors and capacitors will vary (metal, Film, or Comp) and Capacitors (Orange Drops, Mallory, or Xicon)
D: .125" Thick Turret Board Double Row Heavy Turrets Colors Vary
E: All “Carling” Switches and “Cliff” Jacks (Brand Names & Quality)
F: Most Mounting Hardware
G: 600V Wire Kit

Note:
(i) At times an individual brand of resistor or Capacitor may need to be
              substituted for another type or brand depending on availability and stock.
(ii) Kit comes with everything except a speaker and cabinet
(iii) Delivery time is 1 or 2 weeks depending on volume of sales.
(iv) Hammond power transformer may vary from the one shown.

Introductory Price Offer:

$425.00 No Tubes

$458.00 With Tubes
( including Tube Rectifier )

Does not include shipping

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Combo Back 18watt style

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This chassis is a Fender look but 18watt amps have this type of chassis as well as the lengendary Marshall "blues breaker" combo! This kit can be built in three types of chassis styles, 18watt style to fit existing 18watt cabs-these are the style shown in the pic and are usually 20" long x 6" x 2", the one shown in the pic is a bit smaller about 15" x 6" x 2" long. The second type is the head style also 20" long x 6.5" x 2.125" this chassis size will fit in any head cab out there except a large box. The third chassis is like a eightys style Marshall combo which is an upside down head chassis.

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Top Side

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This is the begining of a new project that is rolling full steam ahead, its called project Mini JCM!
I am building the first one as a combo and a proto-type, the wattage will be arround 15-20 watts approx.

Built on one of my hand bent chassis that I sell, this is .051" thick aluminum. You do need a reinforcement plate if you use any laydown transformer as seen but for a small combo chassis its plenty strong enough if you use end caps as all my chassis have.

What it is not to the JCM:

EL84's with a single input and because of the small chassis size, and the Mods I am doing I had to eliminate the middle pot and the presence pot,
they will still be their in part as a fixed halfway value but built into the board. Also I am and have been cutting a few corners such as a vintage power transformer 280-0-280, a fender choke that I had laying arround, and a 10 watt audio output transformer.

What it is to the JCM:

Same pre amp haveing 6 preamp stages including the phase inverter, and in the same configuration, same longtailed phase inverter, same adjustable bias.

Note that a 18watt TMB only has 5 preamp stages including the phase inverter.

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Inside

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Here I have compleated all the wireing that can be done before the board and pots go in.
I have labled some of the wires to make the job a little easier.

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18 Watt Layout for Pro Jr.

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After building a few amps you learn to do certain things first, like the heater wires and the areas that might be tough to get at after the board is installed.

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V4 V5 V6

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This is where the Mini JCM is different - having EL84 power tubes, so as you see mounted on the tube sockets above are 100 Ohm screen grid 3 watt resistors instead of the 1k that El34 tubes would use. Also different are the 1.5k control grid resistors, the EL34's use 5.6k. I will be using adjustable bias to help keep this project true to its name! I will also be doing my favorite mod to this amp, it won't be stock, but then again most Marshalls are not!

The black resistors are 3watt 1-Ohm 1% and on my layouts are labled R-CB-1&2 for (Resistor-Cathode Bias-1) These resistors are needed if you are going to use the cathode resistor bias method. This is the easy and fast way to set and check your power tube bias.

Much more to come on this project very soon!

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Cliff Jack

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Here are the Cliff Jack details, this shows the RG-174 sheilded input cable that goes to pin 2 of the first pre amp tube V1. The 1-Meg pull down resistor and the cloth covered grounding wire, and Thats all their is to it.

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Inside

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Here is the the Mini JCM with its new board in place. This chassis is 16gauge aluminum and is pretty ridgid in part because of a few design elements such as welded end caps, some thicker cahssis don't have welded end caps, and having end caps provides better shielding. The small combo size also naturally contributes to making a thiner material ridgid. A transformer reinforcement plate was also used. See my parts page for my chassis   Seen Here custom size chassis available just ask. The next best step up from 16 gauge is .063" this is a very nice material to work with and punches nice and is strong. You don't need to spend a fourtune on amp parts, to build a good quality amp!

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HIGH VOLTAGES CAN KILL YOU - ALWAYS WORK SAFE!

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You have to understand how to safely work inside the chassis of a tube amp. Just reading this is not enough, read all links bellow; here are a few tips: Never work on a amplifier that is plugged into the wall socket, always unplug it first! Stand on a rubber mat of some sort or wood never on concrete and don't work bare foot, under the influence of alcohol or any other drug, legal or not for that matter. Here is another good tip: Only probe an amp with you're right hand and with you're left hand by you're side. So if you do happen to take a high voltage shock, the the voltage will not go across you're chest!

Wear Protective Rubber gloves!

High Voltage is stored in the electrolitic capacitors and they need to be discharged!  That's what I'm doing in this pic. These are those large round can's and there usually blue or black. The discharge tool is made of 600 Volt wire with a 3-5 watt resistor of 500 to 1000 ohms. Basically you clip one side to ground then clip the other end to the Pos + side of the capacitor. If I have two cans as seen here then there are actually 4 capacitors 2 in each can, so I will take the time and clamp the discharge tool on all 4. Some cans can have more that 2 as well. Check with you're multimeter set to 600 DC volt setting and make sure the voltage has been fully discharged.

Please read through these two Links:

How much voltage can kill?

A Must Read!

Electrical Safety 1

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Copyright © 2005-2006 by Robert Souza. All rights reserved.