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Decided to have London Power Scaling installed in my Vox AC15HW1

Dr. Lo

Member
Messages
1,412
Jeez that sucker gets loud when it's at its sweet spot, even when running at half power. Have had good results with power scaling before with other Brit-style amps (Marshall 1974, Dr. Z Remedy). Gonna do it again.
 
Messages
406
Jeez that sucker gets loud when it's at its sweet spot, even when running at half power. Have had good results with power scaling before with other Brit-style amps (Marshall 1974, Dr. Z Remedy). Gonna do it again.
Hey I realize that this was posted a hell of a long time ago. But I'm considering Power Scaling for my Deluxe or Super Reverbs and perusing TGP you're post was the only one that had it done as a mod to an existing amp.. Would you mind telling me a bit about how it worked out and if you were happy with it??? Thanks
 

Dr. Lo

Member
Messages
1,412
Hey I realize that this was posted a hell of a long time ago. But I'm considering Power Scaling for my Deluxe or Super Reverbs and perusing TGP you're post was the only one that had it done as a mod to an existing amp.. Would you mind telling me a bit about how it worked out and if you were happy with it??? Thanks
Works great! I'm much happier with power scaling than I had been with various power attenuators (2 Webers and Bad Cat's Unleash) in terms of "feel." Getting the same sound at lower volume that you get at high volume involves finding the right position on the master volume (MV), which you would have to install on your DR or SR when installing the power scaling. The MV controls how much signal is sent from the preamp to the power amp. When lowering the power scaling knob, you are reducing voltage being supplied to the power tubes. This reduces output but also makes it easier for them to be overdriven by the preamp signal. Therefore, if you lower the power scaling knob quite a bit but do not also lower the MV, the preamp signal will be too much for the power tubes, causing them to distort much more than under normal (high volume) operation, which can lead to a rather fizzy, undefined type of sound. The trick is therefore taking the time, through experimentation, to find the MV position that provides the sound you prefer at lower power levels.

The MV must be of the "post phase inverter" kind. It is NOT the same as the "volume" knobs on your DR or SR. Those knobs only control the amount of signal that hits the first preamp tube.

Please also know that if your high volume sound is significantly influenced by speaker breakup, this aspect of your sound would be missing when scaling back the amp's power.

Relatedly, power scaling is of most value when your preferred sound relies significantly on power tube distortion. If you do not prefer the sound of your DR or SR when the volume control is high enough to cause natural amp overdrive, then I doubt you would get much value out of power scaling.

Hope this helps.
 
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