Marshall – Valve Tube Guitar Amps

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Marshall JPM50 Re-Commission

  A Marshall JPM 50 arrives in the workshop.  This blog covers this  Marshall JPM50 Re-Commission. This Marshall  JPM50 Amp is from the classic era of pre-1973 Marshall amps. It is therefore highly desirable when fully operational.   The Marshall JTM50 on its last period of production, was re-branded as the Marshall JPM50. The amp went …

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Marshall JCM900 Breaking Valves

A Marshall JCM900 Breaking Valves was the cause of this amp’s failure. It travels around a lot and it has the original 1990’s valve retainers on the output valves. The original ones fitted to this 4102 model are shown below.  These are fitted over the 5881’s to hold them in place. The issue is that …

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Marshall JCM900 Chassis image

Marshall JCM900 100 Watt Combo

A Marshall JCM900 100 Watt Combo  arrived in the workshop.  This version is the 4102  It was very poorly. The first issues seen were : 10 amp fuse in the plug!! Low power output and VERY  loud mains hum Pots noisy Amp plays a dying gasp when amp switched off Pops / crackles and very low …

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Marshall JCM2000 DSL amp image

fix-Marshall JCM2000 Bias Drift

The early (1997-2003) Marshall JCM2000 DSL50, DSL100, TSL100 and TSL122 amps are often troubled by an unstable bias (drifting bias). These are nice amps and I have one myself This can be difficult to diagnose correctly, as it can take half an hour or more of testing and/or playing before this Marshall JCM200 bias drift …

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