Plexi6v6 build pic and clip

[deiseldave]

My 14 year old son, and I finished our first amp together. Thanks to everyone here that helped us, and especially Mark Huss. Pic and sound clip attached. I set the amp at a volume that was clean when picking light, and dirty when I dug in. Thanks again, everyone.

[statorvane]

What a great father and son project. Sounds very good!

[deiseldave]

Thanks. I posted a video presentation with some more clips on youtube.
https://www.youtube.com/watch?v=MGA1FbN ... e=youtu.be

[dcribbs1412]

Congrats deiseldave
very cool father and son project

Darin

[Ken Moon]

What a nice thing to read this morning - my hat is off to you and your son

[deiseldave]

Thanks everyone. I think I still have some tweaking to do. But, it is 85% there. The amp's distortion seems a bit fizzy to me, and when I get much past the AC/DC gain level (past 12 oclock on both volumes), it starts getting a little farty/flubby. I've never played a 1959 before, so I don't really know what is normal, and having 6V6 output may be the issue. The 6v6's may just be falling apart.
I'm open to any ideas. Thanks again.

[deeder]

Bravo DJ !
Liked very much your yt prensetation of the story.
So deiseldave, did you have jumpered the inputs?

[deeder]

Double post...

[deeder]

... Triple post, humm...
I'm very sorry.

[deiseldave]

Yes. Internally jumpered inputs.

[statorvane]

From my experience (6V6 Plexi - I later replaced w/EL34s - I used big Iron from the start) the normal channel is really bass heavy. I don't think the 6V6s are the issue. On just the normal channel alone and with a neck humbucker (SD Jazz), it sounded more like a bass than a guitar - that's with the gain rolled up. You could try lowering the cathode cap on V1 to 22 uF or even lower. I went as low as 4.7 uF for a while. I am currently around 22 uF. I have a switch that can split V1s cathodes (like a 1987) or share them (like a JTM45)

Other than that, stiffer power rail filtering helps reduce the flubby bass. I have 3 dual 50 uF JJ cap cans in mine. SS rectifier.

[deiseldave]

The cathode cap for V1a (normal) is currently 680nf, and the cathode cap for V1b (bright) is 220uf. Which one are you suggesting I change? Thanks.

[statorvane]

Okay. That's about the same as a 1987. Try lowering the 220uF to 22uF and see how you like it. You can go lower. Here's a link to a simple calculator to evaluate the effect of varying the value of V1 cathode bypass capacitor: http://www.ampbooks.com/home/amplifier- ... capacitor/ Frankly, the calculated change from 220 uF to 22 uF doesn't show much difference in the graph, but you can definitely hear it.

Also, you can lower the coupling cap from each triode in V1A. I think you are probably using 0.0022 uF for the bright channel and 0.022 for the normal channel. You can try lowering the normal channel's coupling cap to 0.01 uF. That will reduce the bass from the normal channel.

You don't want to eliminate the tonal differences between the channels, just tighten up the bass. Remember the normal channel came from the Fender Bassman, although it used a 12AY7 in V1 rather than a 12AX7 like the Plexi.

[statorvane]

Actually the cathode cap for the normal channel should be 220 uF and 680 nF for the bright channel. Unless you have a typo above, that may be part of the issue.

[deiseldave]

It wasn't a typo. I went by Mark Huss' schematic, here: http://mhuss.com/Plexi6V6/Plexi6V6c.gif
He shows V1a with 680n and V1b as 220u. Are you saying that is an error in the schematic?