Marshall Master PA - Schematic Needed

Asaf Smilan

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Hi, I got this Marshall Master PA amp for a repair and I'm looking for a schematic for this model. In all of the Master PA schematics I found online (and in all other Marshall amps from the same era) there is a 1M grid leak resistor.
In this amp there is no resistance between the input to ground.
I've been looking on some other pictures of same amps and all have the same arrangement of components on the eyelet board, so I don't think that someone have removed the grid leak resistors.
This is why I think that the schematic I found online doesn't matching to the amp that I have.
Anyhow one of the EL34 tubes that came with this amp is dead, so I'm about to order a new set of EL34s, replacing the 1K screen resistors to new ones and replace the old electrolytics.
If someone have the right schematic for this amp' please post it.
241671987_527589198547136_4713804055430253720_n.jpg 241650690_590511448979642_2618134088743962153_n.jpg
241669369_953826685165718_937146166047553554_n.jpg
 

TAZIN

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You mean the 1 Meg resistors normally found on the input jacks? If so, the Master PA's didn't have them so it's a schematic error.
 

Asaf Smilan

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You mean the 1 Meg resistors normally found on the input jacks? If so, the Master PA's didn't have them so it's a schematic error.
I got it, it really seems like the preamp and phase inverter stages are identical to this schematic (except for the 1M grid leak resistors that not exist in reality).
Marshall-2002-JMP-Master-PA-Schematic-1.jpg
 

Asaf Smilan

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Thanks for the correct schematic!
Do you think that adding 1M resistors between the inputs to ground will improve the amp?
 

Pete Farrington

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Yes.
As it is, the amp will malfunction if something that doesn’t have a resistive path between the tip and sleeve of its jack plug is connected. eg a Rangemaster.
 

Asaf Smilan

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The new caps and output tubes has arrived, I've also installed the 1M grid leak resistors and this amp work and sounds great.
Thank you all for your comments.
 


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