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Half Power Switch on Marshall 2555 Jubilee

Ronstrat63

Member
Messages
83
I love my tone from this amp but find the half power switch on my 100W head pretty useless. At the low power setting the amp sounds thin and lacks punch. It sounds much better with switch on full and the master rolled back.

I have an Airbrake which at two clicks down has the same volume as the switch at half power but sounds so much better (actually pretty close to unattenuated).

Is this my amp or is a problem with the switch circuit design?
 

blackba

Platinum Supporting Member
Messages
11,914
I have a marshall 2553 (50Watt) and I also find the half power switch robs tone like you are describing, I think it is just the amp design. I haven't seen a schematic to know what the half power switch is doing....
 

JerryP

Member
Messages
441
The half power switch is a triode/pentode switch. At half power all 4 power tubes are running as triodes.
Jerry
 

Troser

Member
Messages
41
Pull the inner or outer tube pair, and cut the impedence in half... for instance, pull the inner pair, and switch to 8 ohms while plugged into your 16-ohm cab. That'll give you a lot more growl and sing at slightly-attenuated volumes.

I've got the same head too. ~Tim
 

Ironman

Member
Messages
798
High power (pentode) sounds best...that is if you want the most balls out of her. Triode mode is too soft and just overall lacking for me.
 

mmorse

Member
Messages
961
I have a 2550 and experience the same thing. I also had a little Winfield head that had a half power switch. It too suffered when in half power. I think it's just the way the whole pentode/triode thing works. At half power it's not that much lower in volume but it thin outs way too much. It loses the grunt and lower mids. I'll bet it's even worse with the 100 watt.

As a rule it's the same difference I hear between 50 watt and 100 watt Marshalls. The 50s are almost as loud as 100s but they lack the nice, full grunt and authority of a 100 watter. Of course I'm talking when both amps are turned up.
 

s2khawk

Member
Messages
379
its one of the only bad designs in that circuit besides the diodes all over the crunch channel. I've never heard any guitar amp sound decent in triode mode and thats what 'half power' does here, I mod that switch on the 100watters to just go down to two tubes. If you go to two tubes, you should also switch the speaker out to half of where it was at full power, fyi.
 

yZe

Senior Member
Messages
3,235
varaible voltage regulation (VVR) & power scaling (PS) is it

I'm done w/ attenuators and pen/tri reduction (which was on a demeter I owned)
 




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