THD Hotplate question re Wattage reduction

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SQUAREHEAD

SQUAREHEAD

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So, obviously, I don’t want to blow speakers in any of my old Marshall greenback Pulsonic 4x12 cabs.

So, if I have one of my old Marshall JMP 100W Superleads ‘cranked’, how much will -4dB or -8dB settings reduce actually wattage the speakers will be hit with?

Another words, will I be ‘safe’ at -4dB setting or do I need to go to -8dB?

Thanks for any advice.
 
I believe they cut wattage in half every click. So it would be 0=100w -4=50w -8=25w -12=12.5w -16=6.25-0w. Just remember most that Marshall cranked puts out about 180watts, so doubble the above wattage numbers if it’s cranked.
 
I don't really know if there is a wattage reduction versus DB reduction calculation that can be made but maybe there has been some kind of correlation made in the past. If you feel you are driving them with too much volume then you probably are.

-8Db on a THD hotplate is still quite transparent but still fairly loud with a 100 watt Marshall with all four power tubes installed. Anything attenuation -12DB and beyond you will hear the Fletcher/Munson curve effects which we perceive as tone loss. If you a worried about driving the Pulsonics too hard then it might be worthwhile pulling two tubes to make it 50 watts and then drop your impedance selector to 8 ohms(if you are running a 16 ohm cab) and then use the attenuator to get it to the volume you want. That way you are guaranteed to not be overpowering a 100 watt pulsonic cabinet.

With two tubes pulled the amp will still hit hard like a 100 watter just have less volume. I have run my 68 plexi with two tubes pulled for years now and it really helps to reduce the room volume to comfortable loud room level and I usually don't need more than -8DB attenuation to get it where I want it. For a full 100 watts screaming Marshall with all four tubes you will probably need attenuation levels of -12DB and beyond to get it room friendly, which again starts to affect the attenuator transparancy.
 
Thanks HD & Chubbs!
I agree, 100%, -4 or -8dB cut results in a very transparent situation, but -12dB definitely is the breaking point.
 
I don't believe there is a actual amount it reduces wattage. Different amps would react differently. The dB's is approximate. It's not a exact amount.

David Torn used a Deliverance 120 with a 2x12 with Celestion Alnico Blue. A 30 watt cab with a Hot Plate.
 
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