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Marshall JCM2000 Stable Bias board

Marshall TSL Bias Mod back in stock 28th July

5.00 out of 5 based on 4 customer ratings

Marshall JCM2000 amps when ageing tend to have the main printed circuit board start to become slightly conductive and bias to the EL34 output valves becomes unstable of goes very high and cannot be adjusted.

This  kit totally fixes this issue,

We now offer much faster international shipping options – just enter your country and post/zip code at checkout


Available on back-order

£5 OFF by paying with Moona

Product Description

Marshall TSL Bias Mod

 Our Marshall TSL Bias Mod kit  is for Marshall JCM2000 TSL amps. As the printed board ages, it becomes slightly conductive.  This interferes with the bias circuit on the  EL34 output valves.  The output valves overheat and the bias cannot be adjusted to a stable value.  El34 life is then greatly reduced

This kit totally fixes this issue without the need for replacing the whole main circuit board.

If you know how to use a soldering iron and know how to work on a circuit board then this is an easy upgrade. Some expertise in soldering is needed to install this board. If you are not sure get an amp tech to fit the board

This Marshall JCM2000  kit consists of a little printed circuit board with full instructions and picture on how to fit the road and saves on replacing the whole main board.

This version is designed for the TSL series. There is a version for the Marshall JCM2000 DSL series too. The kits are assembled, stocked, and posted from the UK.

We have fitted  this kit in a Marshall amp ourselves and it completely solved the cooking output valves problem.

The product is supplied with the board, adhesive stand offs to mount the board, and full step by step picture and written instructions. This is not an official Marshall kit but was developed to solve a common issue with this amp series.

There is special drill bit needed to drill the printed circuit board and this is included with the kit.  Price includes post and is sent 1st class post in the UK. We ship this kit worldwide and you can select your shipping option at checkout


The manual was last updated in July 2020.


Fitted Board in a DSL 50 Amp

Fitted Board Example

We can send you a link to the manual so you can review before deciding to purchase. Just email us and we cn send you a link to the document

You should consider replacing your EL34’s as they will likely be worn due to overheating. Check out our EL34 matched pairs and quads from JJ, EHX, Tung Sol

Recent Customer Reviews

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"I’d spent some time upgrading my Blues Junior mk2 with better-spec components; larger pine cab, Cannabis rex, caps & resistors. What difference could alternative preamp tubes make? Well…I’ve already thanked Stewart for hooking me up with these beauties. 7025’s in the V1 & 2 sockets really have cut background noise to pretty-much nowt & any ‘loss of gain’ (I use pedals for this anyhow) is made up for by being able to play at increased vol & greater clean headroom. I lik’em & you might too!." - MH bought EH 7025's and reviewed on 18th July 2021

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"Awesome" US Cusomer S.O. bought Marshall DSL Stable Bias Board kit and reviewed on 18th July 2021

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