Mullard 5-20/Maplin 4-20 modification to NON-Ultra Linear mode???? - diyAudio
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Old 23rd January 2006, 10:39 AM   #1
diyAudio Member
Join Date: Jan 2006
Location: West Coast Of Ireland
Default Mullard 5-20/Maplin 4-20 modification to NON-Ultra Linear mode????

I recently built a Maplin 4-20 Valve Amplifier and I was wondering has ANYONE tried to modify one of these to work in NON-Ultra-Linear mode?
I want to do this because I intend using it for guitar and the Ultra-Linear is too clean. From searching I understand that it's heavily based on the MULLARD 5-20 design so any info on that would be great! Cheers! :-)
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Old 28th January 2006, 04:07 PM   #2
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Join Date: Oct 2005
Location: Lancashire UK
Default Triode mode.

Hi. In the first instance I would contact the designer of the amp for details.His name is Mike Holmes and his web site is at He's a sound bloke and is always willing to help. I have a pair of these amps and if I was going to triode them this is what I'd do. I'd remove the resistor that connects the screen of each output valve ( pin 4 ) to the output transformer. The screen of each valve is then connected to its anode via a 100 ohm resistor.I would run the resistor from pin 4 of each valve base to the output transformer rather the straight to pin 3 as it leaves more room around the valve base.
Good luck, Si.
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