Marshall 4 Hole (plexi or metal panel)

[trem]

Are the 2 channels interactive with just one channel in use? It looks like maybe the volume pots of the un-used channel would have some effect on the channel that has a guitar plugged into it? I am not exactly sure what type of "attenuation" would be happening....
Thank You

http://www.drtube.com/schematics/marshall/1987u.gif

[Chuck H]

I've read where people talk about the interaction between the channels on these amps but as a long time user of a plexi reissue I have found any interaction between the channels to be so small that I have to wonder if I'm actually hearing it. So, even if there is A LITTLE TINY BIT of interaction it seems to me too small to bother considering. Just look at the voltage division ratios considering the mix resistors, through the coupling cap and then the plate load paralleled to the pot loads. It's really mice nuts on paper. And audibly too IMHE

JM2C

[pdf64]

Agree, it's very minor. There's a tone effect also, most noticeable if using a distortion unit into the nomal channel at a low volume setting. Altering the setting of the bright channel volume varies the treble cut filter formed by the 470pF cap that can be grounded by the bright channel vol wiper.
It's best to use a link cable, then this effect becomes unnoticeable.

[Wilder Amplification]

They're interactive in the sense that the position of each channel's volume pot affects the loading provided by the interstage coupling between the channel outputs and the input to V2's gain stage. This happens due to the mixer resistors having different resistances to ground with different volume pot settings.

[trem]

They're interactive in the sense that the position of each channel's volume pot affects the loading provided by the interstage coupling between the channel outputs and the input to V2's gain stage. This happens due to the mixer resistors having different resistances to ground with different volume pot settings.

Thanks John -
Like some of the guys that posted above you, is it a pretty noticeable effect, or is it rather subtle.
I built a 50 watt plexi clone, but I lost the HT fuse while biasing. I have $70.00 worth of fuse, but no 500mA (on order, though I suppose I could use a 10 amp fuse for what I want to do short term....). So I cannot try mine, and I am just curious how usable the effect is in your guys opinion.
Thanks Again