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Making a 50 W Marshall 25/50

11/12/2000 2:55 AM
Making a 50 W Marshall 25/50
This has pobally been discussed a million times, but its been a while since I've been to this part of Ampage. I was just wondering if its possible to mod a Reissue 1987x reissue 50W plexi to a switchable 25/50W. Trace? any input? I can usually figure out how to do this type of stuff if given a rough explanation. If its too complex, do you do this mod, Trace? I'm in connecticut and if I remember your in NY. I love this amp, but this is one thing I would like to have done to it.
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11/12/2000 10:07 AM

Look for the schematic of a 4100 Marshall or a 2555 at schematicheaven; those amps have a power switching.  
As far as I remember you have to switch the power tubes from pentode to triode.  
11/12/2000 12:26 PM

The 25/50 pentode triode switch is working but in triode mode you lose part of the high frequencies and you will get more bluesy sound.  
If you have a 100W amp you can put a switch that would disconnect one tube per side and then you'll get 50/100W pentode sound. In this case however you'll need to adjust the impedance selector to cancel the impedance mismatch between the output transformer primary and secondary that is caused by the elimination of the tubes from the circuit./for more info on the subject check THE TUBE AMP BOOK /
11/12/2000 12:44 PM
BIG Dave

Before you do this, please be aware that 25 watts is not half as loud as 50 watts. In fact, 25 watts sounds about 80%-90% as loud as 50 watts. If you are trying to get distortion at a lower level, perhaps you should try a Marshall PowerBrake or a THD Hot Plate. Either unit can be had for about $200 on the used market.
11/12/2000 9:50 PM

Thanks for all the comments./ My reason for wanting to do this is that at band practice, I need the amp to be a bit quieter. I don't want to get another amp for BP. not just cost, but I believe in getting to know your amp at practices. Keeping practices the same as at a gig.

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