aronimus 7/31/2018 4:44 PM
Marshall Valvestate 8240 clean channel tube driven?
Hi guys

I own a Valvestate S80 8240 which works sweet.
On a forum somewhere I read that the clean channel on an 8240 doesn't run through tube preamp, it's only used for distortion.

Hoping someone can read this schematic better than I can as my skills are rather limited beyond being able to identify components.
I can't actually see where the clean / OD switch is so can't figure out whether there is any truth to this.

Schematic attached.

Anyone know if this is the case, or can tell from this schematic?


Enzo 7/31/2018 4:59 PM
Your input branches into the two channels right after C1, the input cap. The upper branch is the clean, starting with IC2b.

The other branch is the line from C1, down to IC2a. Note that that strip of circuit includes the tube's two triodes. The upper clean strip does not.

The two channel circuit strips continue to the right until they meet at IC5a/IC5b. A control voltage fed to pin 1 of that IC determines which channel comes out.

After that, the preamp signal proceeds through the FX loop, the reverb and chorus, and eventually to the power amp.

So they were correct, the tube is only used on the distortion channel.
aronimus 7/31/2018 5:15 PM
Legend! Thanks for the speedy reply.
drewl 8/2/2018 7:31 PM
Schematics are like a road map.

The more you study them the more they make sense.