7ender

Hello to you all ,

My name is Sjors , ....and my nickname at the dutch Bass Guitar Forum is "MR. LEE".

I'm the one , who overhauled the Marshall Plexi bass guitar amplifier , which belongs to Phil ( alias "Bloc Riff Nut " )

I had really no idea ,  that you guys should visit my repair thread at the dutch BGF.

Well , ...I'm sorry to tell you , that in the meantime  , I've  removed the complete thread ( "Op de Reparatie-tafel van MR. LEE" ="On the working bench of MR. LEE ) , due to a quarrrel in a thread about politics , in which some dutch forum-members called  me racist and a nazi ( and some more ) idiot stuff like that.

So a couple of people accused me to be a racist , which i'm NOT !

It made me so angree  , that I decided not to give  repair-explanations and pictures of repairs , or any other support for repairs at that dutch forum any more.

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If you peope in the U.K. have any kind questions about amplifier problems  , I'll try to be helpful to you..

Very friendly regards ,

Sjors ( MR. LEE )

The name of that  phenomenon , what you discribed as "thudding noise" is called :  "motorboating".

"Motorboating" is in fact a low frequency feedback ,...and in this case , it will be caused  due to a lack of capacity of one ( or both ) filter capacitors , located in the the power-supply section of the amp .

So , mister Bill Fitzmaurice was right ! ,....it's just a simple faillure , and it's very easy to fix :

Just re-solder the solder-joints of these capacitors , ...and your amp-problem will be solved ! 😉👍

Be sure , there's no standard/table lamp with a dimmer at the same mains group

Sometimes a "dead spot" will disappear when you just place te bass-guitar in a corner of the bathroom ( not under the shower of course ) , just for a time of two days . By placing it in a steamy environment for a short period of time , will recover it, , and you will hear that the sustain of the tone is back again . Sometimes it will be okay for ever , but don't be too disapointed when it comes back again within a couple of weeks/months. Dead spots will mainly occure in bass guitars with rose-wood frett-boards . I've had troubles in the past with bass guitars of several brands/types like : Musicman Stingray , Yamaha BB1100S , Fender Jazz Bass (japan) What I think is , that it maybe has something to do with a not solid attachment of the rose-wood layer on the maple neck , wich consist of different types of wood , with different expansions. For a good repair , you have to bring it to a guitar builder for a frett-board replacement. ( sorry for the bad English , but I'm dutch )