How can I get power sag without using a tube rectifier?

Series resistor.

Hey - is Canada Heaven, or is Canada South of Heaven?

 

Not really... I'm talking about inside the amp, after the wall voltage has been stepped up by the transformer and turned into direct current by the rectifier. A mod that really should be done by a tech, and would of course affect the originality of the amp.

Heh heh, I get it, in that case this whole world is South of Heaven. I guess you got dibs on that as a band/album/song name.

 

The mod I've seen puts a 100 ohm, high wattage resistor in between the rectifier output and the first filter cap. To bypass it, install a switch so that when the switch is closed it shorts out the resistor. It wouldn't affect the sound of the amp at all when bypassed.

 

WeberVST also has a copper cap module rectifier that needs to be installed inside your amp. You can purchase them to emulate a multitude of rectifiers.

http://www.webervst.com/ccap.html

 

I'll repeat myself, there are module versions of his rectifier that need to be installed inside the amp. They replace the solid state internal rectifier, no tube socket required.

 

Hmm,
that's quite interesting. Pretty much I can swap my Mesa's soid state rectifier with one of these bad boys and have it sag like a tube rectifier. Is this mod possible to be done by everyone or just a tech? Thanks for the tip Jeff,

Vlad

 

The mod should be done by a tech. If you made a mistake you could easily take out your power transformer.


Jeff

 

Yes it could be done. How easily depends on how the inside of your amp is layed out.

 

Switching rectifier schemes will impact the bias. The original bias circuit will have higher B+, and thus draw more plate current than the sag inducing rectifier thingy.

 

Swarty is right. If you wanted to switch and use the 5U4 version of copper cap the B+ change between the two would probably be a little too large to have the tubes biased up properly in both settings. A 5AR4 version of the copper cap would work better. You could find a bias setting that would work with both B+.

The thing you have to think about are you looking for the SAG effect of a tube or the voltage drop of a 5U4. The voltage drop from the 5U4 copper cap will definately change the feel/tone of your amp along with the simulated SAG you are looking for. Lower voltage usually means slightly warmer/darker and less head room.

 

SAG is what happens when the rectifier isn't able to keep up with demand.

So what you are looking for might be either, the amp running at a lower B+ or the effect of SAG. You have to push the amp a little to get the rectifier to SAG.