How to repair a Marshall JMP 2104 with many problems

Let's repair this Marshall JMP 2104 amp. It has many issues. Some caused by age. Some caused by poor previous work. In this video you will learn how to improve Marshall's grounding, how to replace that awkward capacitor under the PCB, and how to bias an amp using an oscilloscope.

You will also meet my beautiful 1971 black Les Paul Custom called “Doug”, named after my first guitar hero, Doug Ford. Doug Ford and (Beano) Clapton epitomize the perfect Les Paul tone to me. I asked Rod McQueen of Sliders pickups to make me a set of PAF for “Doug”. I love the tone!

The completed JMP 2104 sounded fantastic. I hope it came across on your speakers.

Here are a couple of links referred to in the video:

Sliders Pickups: https://sliderspickups.com/product-it...
Doug Ford and the Masters Apprentices:    • Видео  

Chapter Index:
00:00 Introduction
01:05 Initial Inspection
03:20 The curse of WD40
04:20 Improving the Marshall ground
06:40 Missing bolts on Output Transformer
10:00 Soldering a chassis ground
15:40 How to replace a Marshall capacitor that is under the PCB
16:50 Schematic overview of the output stage and bias circuit.
18:40 Upgrading the bias capacitors and precaution in not overdoing it.
25:50 How to test for leaky coupling capacitors
31:35 A common cause of signal guitar cutting out
35:40 How to make a tool to clean input jack contacts
37:25 How to bias a Marshall by plate current and oscilloscope methods
38:50 Try different tube positions for a better match of the plate current draw.
40:07 Setting bias with an oscilloscope
49:13 A beautiful pair of original Rola Celestions
50:25 Revision of bias caps and summary
51:50 Homage to Doug Ford and my Les Paul called “Doug”
52:25 Sound Test of the completed Marshall 2104
54:26 End