tube amp power scaling

[REPTAR]

Anyone know anything about this?  Jackson amps' Scarlet 30 has this power scaling attenuation thing.
I'm thinking of building a blackface bassman clone sometime in the future, and would love to add something like this to it.  Also any recommendations for parts sources, mods, etc. for amps would be very appreciated.

[davent]

You should check out Dana Hall's VVR circuit, has a few differnt ones available for either fixed or cathode bias, not sure how big an amp they'll accomodate.

As well check out the Power Scaling kits available at London Power. http://www.londonpower.com/pscaling.htm

dave

[gordo]

+1 on the London Power site.  I bought the book on the theory of it and it gave me a really bad headache but Kevin O'Connor goes into crazy detail on how it works.  I've yet to try it but my old JMP 50 watt Marshall got the Dan Torres mods back in 2000 (which is what got me really stoked about building pedals after sweating my way thru modding an amp) so it sounds killer but still needs to be loud to be a Marshall.  I'd like to power scale the old beast to see how it sounds and for the most part it's minimally invasive and reversible.  Just need to keep the heat issues in check.  I'd like to do away with the master volume.

[fish22]

Keefe etched me a small VVR (power scaling) PCB and it worked really well on my Dr. Z Carmen Ghia.
I used the Hall Amplification circuit. pretty easy to implement as well!
I only went the DIY route when Hall didn't answer my email for over a month.
If you can still get the hall I would do that because the DIY route isn't cost effective once it's all said and done.

I need to go back and replace the wire with some solid core wire, this was all I had at the time.

[jubal81]

Cool stuff. I'm thinking about trying this out. I'm tempted to replace my master volume with it instead of mounting it on the back. Is there any reason to keep MV if you have VVR?

Also, do you like how it's performing?

[REPTAR]

Thanks for the response guys!
fish22, how does it sound?

[fish22]

Cool stuff. I'm thinking about trying this out. I'm tempted to replace my master volume with it instead of mounting it on the back. Is there any reason to keep MV if you have VVR?

Also, do you like how it's performing?

Well lets start by saying I am not an amp guru... I'm just a tinker-er that has a little tiny bit of amp knowledge. Just enough to not kill myself basically.
The VVR does what you would think a master volume would; it keeps whatever tone you have going and reduces volume according to where the VVR is set.
For what I wanted it to do, it works well. I wanted to get the Carmen Ghia into a slightly broken up sound without crazy volumes that it might take to get to breakup. I play mostly in church settings or settings where I'll be mic'd. And since I'm a sound man too, I know how annoying loud guitar amp stage volume can be. I wanted to keep my amp in a sweet spot, but not be too loud.
My Dr. Z Maz 18 has a master volume, and on the Maz at least, the MV works very well so I don't really feel the need for the VVR on it.
Correct me if I'm wrong, but I think there are different approaches to Master volumes so I'm not really sure if you could replace a MV with a VVR...
Not sure how Dr .Z master volumes differ from other MVs, but the Z master volume seems to work very well.
But if you have a non-master volume, cathode biased amp, I'd recommend trying it.
This guy's video shows how mine works:

[nzCdog]

Thats a sweet demo!  Great how you can hear the volume change, unlike in many youtoobs where it gets compressed to the same level

[nzCdog]

My understanding is that MV attenuates the signal going into the power tubes, VVR attenuates the plate voltage of the power tubes, causing them to saturate at lower levels, limiting their output.