Reducing Power Supply voltage

[graphitiac]

It seems that most people want to increase the head room and output of an amp if possible. One way to do this is to increase the power supply voltage if the tubes will take it. Can you go the other way -- reduce the effective power supply voltage without replacing the the Mains transformer? The purpose would be, for example to use 6V6s in a 6L6 amp, or to reduce the headroom so that you get distortion sooner at lower volumes. It seem to me that adding a resister right up front between the rectifier and the first filter cap would do this. Does this work?

[mooreamps]

It seems that most people want to increase the head room and output of an amp if possible. One way to do this is to increase the power supply voltage if the tubes will take it. Can you go the other way -- reduce the effective power supply voltage without replacing the the Mains transformer? The purpose would be, for example to use 6V6s in a 6L6 amp, or to reduce the headroom so that you get distortion sooner at lower volumes. It seem to me that adding a resister right up front between the rectifier and the first filter cap would do this. Does this work?

A resistor could work, but you have to figure the I squared R losses to calculate the wattage for the device, along with the resistance to calculate the voltage drop. Another way is to use a 5 watt zener in series to drop the voltage as well, in increments of ; I would say no larger than 25 volts for each device. However, in my equipement, this is what I use my electronic power brake for. .

-g

[graphitiac]

"this is what I use my electronic power brake for. . "

Are referring to a power attenuator that goes between the OT and the speaker? That would not affect the response of the tubes would it? Thanks for the advise about the Zener.

[mooreamps]

"this is what I use my electronic power brake for. . "

Are referring to a power attenuator that goes between the OT and the speaker?

No, is not a power attenuator. It is electronic power scaling that regulates PA power tube plate current.

That would not affect the response of the tubes would it?

It does not affect the response of the tube. It plays on how a pentode power tube works ; electrically.


-g

[tubeswell]

You can also zener down the B+ with a few reverse-biased 5W 15V zener diodes in series with the HT CT to ground. Try 2, 3 or 4 and watch those Vs drop away... (This way is also better than a hefty resistor in the B+ line, because you don't eat up any current)

[graphitiac]

Well this is all very interesting. I'm pretty new to this. I've never heard of a "power brake" and I haven't been able to find any reference to them. I'm was planning to build a 5E3 -- it should have more than enough volume for me most of the time, and I want it to break up. But I know sooner or later I know I'm going to be in a situation where I'm out-powered. So now I'm thinking about one of the beefed up versions that use 6L6s or other higher powered tubes, but I'd like to be able to ramp it back for small venues and practice, maybe with a switch and swap out the tubes, instead of having to have another amp. It seemed to me that a resistor would work because they are used in the HT line anyway to bring the voltage down for the other smaller tubes. But your ideas sound good. Thanks.

[graphitiac]

"I've never heard of a "power brake" and I haven't been able to find any reference to them."

Update that: I have now found PowerScaling.com.