Marshall Origin 50h Static Noise

cgtrman

Member
Joined
Aug 29, 2011
Messages
32
Reaction score
13
This amp might be my fave amp of all time, but I have a recurring issue. When I first power it up, there is 20-30 seconds of static and white noise regardless of anything connected to the input. It will die out and not return until my next power-up.

A friend suspects a plate resistor might be to blame. Im hoping a preamp tube is the culprit. Any recommendations?
 

ampmadscientist

Well-Known Member
Joined
Jun 26, 2014
Messages
17,857
Reaction score
12,167
Location
Bio-Isolation Lock Down
This amp might be my fave amp of all time, but I have a recurring issue. When I first power it up, there is 20-30 seconds of static and white noise regardless of anything connected to the input. It will die out and not return until my next power-up.

A friend suspects a plate resistor might be to blame. Im hoping a preamp tube is the culprit. Any recommendations?

This is not normal, and it is not " what tubes should do."
Replace the preamp tubes one at a time with a new 12AX7 and re-test the amp every time you swap one out w/ the new tube.
If there is a bad tube you will find it.
Most common cause of crackle in guitar amps is the preamp tubes. (it's usually one tube that does it)

2. If the sockets contacts get oxidized it can also cause this to happen.
A small amount of Deoxit G100 in the socket contacts will cure that problem.

3. There is no reason to imagine that this is caused by a resistor.
You need to find evidence before you reach that conclusion.
Repairing guitar amps by guessing / random parts replacement generally gets you nowhere.
It is "possible," but more commonly it's a preamp tube that's causing it.
And I say this based on long term experience not guessing.

4. Plug a guitar cable between send and return of the effects loop. Then re-test the amp.
 

Phony iommi

Well-Known Member
Joined
Mar 16, 2019
Messages
566
Reaction score
1,114
This is not normal, and it is not " what tubes should do."
Replace the preamp tubes one at a time with a new 12AX7 and re-test the amp every time you swap one out w/ the new tube.
If there is a bad tube you will find it.
Most common cause of crackle in guitar amps is the preamp tubes. (it's usually one tube that does it)

2. If the sockets contacts get oxidized it can also cause this to happen.
A small amount of Deoxit G100 in the socket contacts will cure that problem.

3. There is no reason to imagine that this is caused by a resistor.
You need to find evidence before you reach that conclusion.
Repairing guitar amps by guessing / random parts replacement generally gets you nowhere.
It is "possible," but more commonly it's a preamp tube that's causing it.
And I say this based on long term experience not guessing.

4. Plug a guitar cable between send and return of the effects loop. Then re-test the amp.
Not to divert the op here, but what diagnostics does plugging a cable into the send and return of the fx loop provide? What should happen when you do it?
 

cgtrman

Member
Joined
Aug 29, 2011
Messages
32
Reaction score
13
Thanks for all the great feedback and recommendations. I will start w swapping preamp tubes one at a time.
 

cgtrman

Member
Joined
Aug 29, 2011
Messages
32
Reaction score
13
Would a preamp tube exhibit statis and white noise as it warms up, then go away?
 

Arc Anjil

Active Member
Joined
Dec 26, 2012
Messages
147
Reaction score
127
Location
Florida
My O50h does that hissing noise on power up/warm-up, too. Only on the 50 watt setting, though, not the 10 watt. I've rolled the pre-amp tubes and nothing has changed.

Once warmed up it's all good.
 

cgtrman

Member
Joined
Aug 29, 2011
Messages
32
Reaction score
13
My O50h does that hissing noise on power up/warm-up, too. Only on the 50 watt setting, though, not the 10 watt. I've rolled the pre-amp tubes and nothing has changed.

Once warmed up it's all good.

Interesting. Mine occurs on all three pwr settings.
 

cgtrman

Member
Joined
Aug 29, 2011
Messages
32
Reaction score
13
I never use the fx loop. I place a jumper in fx loop and the noise and static are the same. What is the purpose of that test?
 

cgtrman

Member
Joined
Aug 29, 2011
Messages
32
Reaction score
13
I replaced each preamp tube one at a time, no change. I will replace power tubes tomorrow.

One more clue: it makes static and intermittent white noise w master vol at zero.
 
Last edited:


Top