Who did the mod?I have 2 JCM 800's that are modded with an extra tube. Its a great mod that adds 2 tube gain stages when engaged. What is so cool about it, is that with the push pull pot (extra tube), disengaged it is a bone stock JCM 800. Literally bone stock with zero changes to the original circuit. Can anyone guess how this is possible? With the extra stages engaged the amp cleans up better than any mod I have played to date. From clean to crunch to ripping high gain with hardly any change in volume.
Me too...
Very possible. I have one of my mods set up just like this. Pull the second gain control and it disengages the 4th gain stage, totally out of circuit. Push it in and it’s fully engaged. Not that difficult really.I have 2 JCM 800's that are modded with an extra tube. Its a great mod that adds 2 tube gain stages when engaged. What is so cool about it, is that with the push pull pot (extra tube), disengaged it is a bone stock JCM 800. Literally bone stock with zero changes to the original circuit. Can anyone guess how this is possible? With the extra stages engaged the amp cleans up better than any mod I have played to date. From clean to crunch to ripping high gain with hardly any change in volume.
Mine is not all stock but that doesn’t matter. It could be and it would still work. I inserted the extra stage between the factory second and third stages. You just break the connection with a switch and it’s like the extra stage was never there. Just like anything else on a switch.So all stock JCM800 with an added fourth gain stage? Where does the stage come in to the circuit? When the added gain stage is not engaged, my mods are 100% bone Stock JCM800 circuit. Zero changes to the stock Marshall. My amps add 2 extra gain stages with the added tube.
The mod utilizes the horizontal JCM's. I'll be glad to post the circuit pics. I did this one Paul. It's a slightly tweaked copy of an Elan Memran modded Marshall. It brings the added two stages in right before the cathode follower after the existing three gain stages. The tone stack becomes extremely sensitive to adjustments and the amp cleans up better than any other mod I have owned.Who did the mod?
Exactly. I was surprised at the changes to tmb sensitivity by placing the stages before the follower after the existing three stages. As well as what It allowed as far as the amp cleaning up. On the unreal side actually.Mine is not all stock but that doesn’t matter. It could be and it would still work. I inserted the extra stage between the factory second and third stages. You just break the connection with a switch and it’s like the extra stage was never there. Just like anything else on a switch.
The amount of stages added doesn’t matter either. If it’s only one extra tube, yours is just taking signal into one grid of the extra tube, coming out of the plate of that side, into the grid of the other side of the extra tube and out of that plate back into the circuit. You’re coming back in with a much more amplified signal to drive the rest of the circuit.
Of course it has cathodes connected on both sides, B+ to the plates etc…but that’s the general idea.
It does. All stock except the added stages. The stock green grid leads are just replaced for shielded cable but still as stock.that looks really interesting.... you said it keeps the cathode follower right?
This feels right. I've heard 800's that are full and rich, and I've heard ones that sound brittle and shrill. A lot of people will talk about the vertical vs horizontal inputs as a cause of this, but honestly there were great vertical 800's made and awful vertical 800's made; just like there were great horizontal 800's made and awful horizontal 800's made.Not all 800’s sound good either. This is probably why some are satisfied with a stock one and some aren’t. Probably 15% of the stock MV Marshalls I’ve had sounded killer 100% stock. The other ones were marginal and needed some minor mods to sound good. Component variances, component changes, hot shield inputs, etc, etc….will all change the outcome of a stock amp.