Marshall 18 Watt Clone Circuit and Mods 

Awesome! How much difference did the choke and Mercury Magnetics transformers make? I thought about putting a choke in the power supply but I wasn't sure if it would be worth it. I almost did the extra gain stage mod but chickened out.

@@thetuberoaster8321 The choke makes a pretty good difference in the lowend. The mercury transformers sound great, but propably less difference than the choke was. I just did a cascade mod this weekend on mine and wow it transforms it into a monster haha. I'll definitely need to put this mod on a switch since it's so different.

Thanks! The cost I always find to be most prohibitive. I haven't made very many guitar amps simply because they're so expensive. It's the transformers that are usually the most costly. For Hi-Fi it's even worse, everything must be low noise and have good bass and high end. However, I think it's possible to build a relatively simple amp from a kit even if you don't really know what you are doing. Most valve circuitry is actually quite simple once you get the hang of it. It did take me a while to become familiar enough with this amp to attempt to mod it or fix its latent problems.

It would involve adding another 12AX7 tube for the effect send and effect return. There are two ways to make an effects loop. Series and parallel. Series simply sends the signal to the effect and the return valve picks it up. Parallel would mix both the wet and dry signals before the return amplifier. The only thing is that parallel requires a dual-ganged "mix" pot that would need to be mounted somewhere. The series setup would only need an input and output jack. I'm sure you could make room on the back somewhere. The actual circuitry is not that much different for a parallel than for a series setup. As far as circuit placement, perhaps you can put it after the TMB tone stack if you are doing the TMB thing or the tremolo amplifier tube if you are doing tremolo. As an aside, you might have better luck if you somehow make a global feedback loop to the phase inverter tube. I'm not sure how familiar you are with the circuit, but there are two inputs on the phase inverter. One connects to the normal channel and the other connects to the TMB/Tremolo channel. Normally, one of those two inputs is the negative feedback coming from the output stage. If you made the normal channel have the effects loop and the TMB or something, you would free up that input for the NFB. The reason I mention this is because the amp will sound more "3-D" with NFB and have more headroom. It will also probably take effects better. The normal Marshall 18 watt circuit has no NFB and it makes everything sound crunchy. It works great for some sounds, but I personally think NFB would make it sound much better. I haven't (successfully) attempted this mod because it involves reworking the entire preamp section, but since you haven't built your's yet, it might be worth considering.

There's a demo video where I show how it sounds with timestamps for different tubes and guitars. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Y5hRXiXaoD0.html