Mojotone Custom 50 Amplifier Kit


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SKU: 0755545
Weight: 30 lb
Sale Unit: Piece

In Stock


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Please read our article 'Mojotone Amp Kit Building Primer' along with our amp kit disclaimer located in the Specs tab before buying this kit.

The design was a labor of love that started in a garage in New Malden, England. It quickly grew in local popularity, and made its way to the stage behind big names like the Who, Pink Floyd, Jethro Tull, the Moody Blues, and Manfred Mann. The legendary DR504 is synonymous with big, clean, and powerful.

Skilled amp builders, try your hand at recreating this sonic icon with our Mojotone Custom 50 amplifier kit.

The kit comes with everything necessary to build a working unit, including resistors from Ohmite and Vishay, Mojotone Dijon capacitors, Heyboer transformers, Belton tube sockets, and potentiometers by Alpha.

Also included is a full-color wiring diagram which provides a faithful road map of all the right angles and mil-spec techniques which were documented from studying two original examples from the early seventies.
  • Class Type: AB All Tube Amplifier
  • Output: ~50 Watts
  • Circuit: 1970-1972 DR504 Custom 50
  • Bias Type: Fixed Bias
  • Build Time: ~8 hours
  • Preamp Tubes: ECC83/12AX7 (3) & ECC81/12AT7 (1)
  • Output Tube(s): EL34 (2)
  • Rectifier Tube: None - Solid-state Rectified
  • Transformers: Power - Hiwatt 50W (MOJO786), Output - Hiwatt 50W (MOJO785)
  • Hardware:Mojotone Custom 50 Small Parts Kit, Custom 100 Chassis, Front & Rear Faceplates, Octal Base Clamps, 10' Removable Power Cord

Disclaimer: Some of the parts contained in this kit are subject to availability.

Mojotone reserves the right to change or substitute any and all of the parts contained in this amplifier kit without advertisement or notification to the buyer. Part substitutions made by Mojotone are guaranteed not to affect the integrity or operation of your amplifier kit. Time estimates listed are from start to finish. If you are new to tube amplifiers, additional time may need to be factored.


When purchasing a kit from Mojotone, you will receive the following documentation.

1. Schematic

2. Wiring Diagram / Layout

Our beginner level kits such as the tweed champ and tweed deluxe include a manual. If you purchase a kit from Mojotone and do not receive these documents, you can obtain copies by emailing or calling 800-927-6656. The Mojotone staff is available Monday through Friday from 8:30 a.m. to 5:00 p.m. EST unless otherwise closed.


Mojotone kits include the best quality parts that are available at the time of purchase. If a substitution is required, our team will use parts that are of equal quality to ensure the integrity of the kit build remains the same.


Building a fully functional amplifier kit is not an easy task. Before building a kit, one should have the ability to properly solder as well as read and understand a schematic and wiring diagram. While we do our very best to ensure all documentation is current, the included documentation is meant to serve as an overall guide to building the amplifier. Simply following the schematic and wiring diagram does not guarantee you will have a fully functional amplifier. In fact, post build troubleshooting is a common issue across all builds.


Our staff is available to assist with basic troubleshooting needs. There are plenty of online videos available that are helpful with most post build issues. Technical staff is available via email by sending a message to You may also call our sales team to discuss build problems, dial 800-927-6656 and press 1 for sales.


Building a tube amplifier takes time, dedication, resources and most importantly... Skills! The experience of building an amp can come with some frustration, the reward of completing the build is definitely well worth your time. Please review the wiring diagram, schematic and manual (if applicable) prior to making your purchase. Mojotone will not accept any returns on amplifier kits and/or parts that have been assembled, soldered or modified.

This amp kit also comes with the following documents. Please feel free to view and/or download them:

Custom 50 Schematic
Custom 50 Wiring Diagram

Other Videos Featuring This Product

Ratings & Reviews

2 reviews

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11/18/2023 2:18 am

Legit kit, worth the effort.

by PK

This is a great kit. I usually drill my own chassis and stake my own boards and do my own thing, but being unfamiliar with Hiwatt type stuff I just wanted an “easy” way to get there. Very impressed with the quality of materials, the exceptional packaging, and the attention to getting things right.

This build is a lot of work (especially if you’re OCD like me and wrap the turrets instead of poking) but the result is excellent. Only two faults that were east to resolve: one end screw hole on the main board didn’t match the chassis hole spacing, and there was an extra 100-ohm resistor that freaked me out for a minute when I was done, ha. Also, be ready (and equipped) to either swap out the bias resistor or add a trimpot. I only got about -32v from the included value, which gave me a toasty 71ma per tube. Easy enough to fix.

Sounds great. Really fun amp. Very loud. Can’t even imagine the 100…

6/13/2022 11:26 am

Great Amplifier, Great Kit!

by Matt -

Thrilled from the moment I unpacked the shipping boxes! Mojo's packing deserves special mention: exceptional padding, all parts neatly organized and labeled.

Suggestions: take your time! Make copies of the layout diagram to mark off components/connections as they are added. Triple check everything before soldering. Before power on, re-check against layout diagram; use a DMM to look for shorts/cold solder joints and continuity.

It sounds great! Despite their reputation for being obscenely loud, Hiwatts do have a very useful master volume. At least for clean tones, it's surprisingly usable at "bedroom" volumes.

Only nitpick is the lack of an adjustable bias. Mojo's goal was to be true to the originals, which did not have an adjustable bias. Today's tubes are not as consistent as the tubes from 40 years ago, and therefore adjustable bias is a must. (The adjustable bias mod is not particularly hard, and well documented.)

In short, I'm delighted with the kit!