'66 Bassman triode/pentode switch?

[grunt]

Mothballed amp that I've recapped, going to get rid of the hum setup for the bias setup, replace a power tube socket, coupling caps, and the power cord. I'm not using the ground switch and was considering a DPDT triode/pentode switch. Looked online and I'm not real clear on the installation from what I've found. Can someone help me with this specific amp in mind? Is it a worthwhile mod, or simply underwhelming? I'm using a new power cord w/ ground and it's fatter than the original. Have you found a plastic clip/keeper/grommet to fix it to the chassis like the original cable? Or just let it come out the chassis w/o this?

My thanks in advance.

[Satamax]

Imho Triode switch is not realy worth it. Use teh hole for a variable NFB for example, or a mid control!

[bob p]

I have a triode/pentode switch on my Mesa Mk IV, and I use it fairly often. Now I'll be the first to admit that its not THAT great a feature -- and I certainly would not consider drilling a hole into a chassis to implement it -- but its a mod that's proabably worth trying to see if you like it. It does allow you to get earlier power tube breakup, and it makes it harder to get loud and clean out of your amp. If you want to get your amp to break up earlier at lower volumes, its worth looking into, but it won't quiet your amp like an attenuator.

I really like the variable NFB mod. Its a great bang for the buck mod, and I perform it regularly when I do ground-switch/death-cap-ectomies. It will also help to get your power section breaking up earlier, so both of the mods we've been discussing take you in the same direction.

IMHO, they both help, but the volume of your amp is still pretty loud in both cases. If more quiet is what you're after, an L-type attenuator is the E-ticket.

[grunt]

Originally Posted by Satamax

Imho Triode switch is not realy worth it. Use teh hole for a variable NFB for example, or a mid control!

Thanks for your input. I'd like to try the NFB mod as well. I'll poke around on the web and get that info. Since this is going to be a guitar head, I'd like to try to get some dirt at lower volumes on occasion. I'd like to try the triode/pentode switch, and maybe keep it, maybe not.

[Satamax]

Well, you can also do this one to the bassman, it's way cool!

http://satamax.free.fr/bandmastermod.jpg

[grunt]

Originally Posted by bob p

I have a triode/pentode switch on my Mesa Mk IV, and I use it fairly often. Now I'll be the first to admit that its not THAT great a feature -- and I certainly would not consider drilling a hole into a chassis to implement it -- but its a mod that's proabably worth trying to see if you like it. It does allow you to get earlier power tube breakup, and it makes it harder to get loud and clean out of your amp. If you want to get your amp to break up earlier at lower volumes, its worth looking into, but it won't quiet your amp like an attenuator.

I really like the variable NFB mod. Its a great bang for the buck mod, and I perform it regularly when I do ground-switch/death-cap-ectomies. It will also help to get your power section breaking up earlier, so both of the mods we've been discussing take you in the same direction.

IMHO, they both help, but the volume of your amp is still pretty loud in both cases. If more quiet is what you're after, an L-type attenuator is the E-ticket.

Thanks for your input and quick response.
When installing the mod, I see a 1K/5W resistor for the screen. Do I remove the stock 470/3W?
The center terminals on the DPDT switch go to these screen grid resistors, while on one of the end set of terminals goes the plate and the other end terminals goes to the original screen grid supply. Is that correct?
I've got an old Tom Sholtz power soak. Haven't broken it out in years. Might still work. I'll try it to get the volume down low when needed.

[grunt]

Originally Posted by Satamax

Well, you can also do this one to the bassman, it's way cool!

http://satamax.free.fr/bandmastermod.jpg

That looks really interesting! and the A/B'ing between dirt and clean is way cool.
Do you have something like this for the mid control? And a picture of your take on a triode/pentode switch installation? Or does it sound like I've got it?

[Satamax]

You might be intrested by thoses links.

http://www.blueguitar.org/new/articl...bluesmaker.zip

http://www.blueguitar.org/new/schem/...d/triodesw.gif 470Ω should be fine.

http://www.blueguitar.org/new/articles/other/pow.zip

http://blueguitar.org/new/schem/fend...4_vs_aa165.pdf

Bye.

Max.

[stokes]

I also feel the triode/pentode thing is somewhat overrated in most amps.I dont have that option on my Boogie MKII,but I can see how it would be more useful in a Mesa like the MKIV Bob pointed out because the Boogie output is biased quite cold,so it would make the power tube breakup more noticeable since you get very little power tube breakup out of a "stock" Boogie the way they bias them at the factory.If you are looking for power tube breakup,and not just trying to quiet the amp,the NFB mod might be better.You could also try a 12AX7 in place of the 12AT7 PI and bias the 6L6's a little hotter.A guitar player I used to play with had a master volume installed in his BF Bassman head which went a long way to accomplish both breakup and quieting the amp,unfortunately I never got a chance to open the amp up to see how it was wired,but it was one of the better functioning MV mods I've seen.