Diagnosis of Marshall 8100 Valvestate head problems

Thread Starter

wolf1419

Joined Nov 1, 2008
117
Hello Ron,

Yes, that is the check if there is no un-balance in the amplifier itself.
If the input is grounded, the output should be 0 Volts.( some mVolts are OK).
If that is not the case there is something wrong.
A DC offset could be bad for the speaker as it is forced one way with no input
AND there is a current flowing through one of the transistors without input.

Greetings,
Bertus
I have 14mvolts at output......with jumper, and same with nothing in input without the jumper....is that reasonable..?
 

bertus

Joined Apr 5, 2008
22,270
Hello Ron,

That should be OK.
The opamp and the other components can cause this little offset.

You can try to make some music.
Start at low volume as said before.

Have fun,
Bertus
 

Thread Starter

wolf1419

Joined Nov 1, 2008
117
Hello Ron,

That should be OK.
The opamp and the other components can cause this little offset.

You can try to make some music.
Start at low volume as said before.

Have fun,
Bertus
That's good news....I'm going to let it run a good while and keep checking heat & voltage...:cool:......worked fine....

It's all back together and makin music........still using line out(same as speaker) at this stage, started easy & able to crank gains & output w/o making loud sound....ran it several times............speakers will be next, when I can make some real noise........Thanks Rifaa for your trick......Thanks for always being there to guide me Bertus!!!!!
I told you I'd make you proud and get this going in the end...well worth the effort.....thanks for teaching, friendship, etc.......
 
Last edited:

Thread Starter

wolf1419

Joined Nov 1, 2008
117
All assembled, ran for hours, on/off...working up to higher volumes....THIS AMP ROCKS!!!!!!!!!! ...................

"All tube guys"(I have some of those also.... JTM30, JCM800, 900, 2000) will still want that character, but Nice job on this Marshall.....design is simple and awesome..............single PCB, not all those various motherboards like my VS Series.....which are also decent...(but don't like the MG series..Cold/brittle/poor tone/lifeless sound)

The 8100 offers Clean/Crunch channel & OD1/OD2 channel...from super clean....really nice..almost Fender like character to light Marshall blues/classic crunch....then Marshall classic rock OD to over the edge OD2 metal/thrash distortion...tight, or loose using contour control, altering midrange totally getting different character as you desire, and all with good tone(no kids buzzsaw distortion here) and a lot of sustain.....
......this can really work for some. Try it, you might like it!!
 

Thread Starter

wolf1419

Joined Nov 1, 2008
117
Top