Power Brake

[ranchak]

Are there any DIY schematics for a power brake?

[hairyandy]

Not that I know of, but check out The Amp Garage forum and search for "airbrake" and you'll find some threads about making your own Ken Fischer designed amp attenuator based on the Dr. Z Airbrake.

Andy

[Dai H.]

if you want a marshall power brake, it'd be cheaper to buy a used one since it uses what I think is basically like a tapped autotransformer. That is not a part you would obtain very easily or inexpensively. Something to consider it that among attenuators, they don't have a particularly good reputation as well. However, IMO it does seem possible to get a good sound using one by making some small alterations. The one shown on the amp garage should be much easier to implement if you're trying to do something DIY'ed.

[dmk]

do tell what these alterations are? 
i use a powerbrake mainly just at home, sounds ok, but i'd never use it as part of a recording or gigging setup.

[Dai H.]

well if you look at Randall Aiken's site and the "Plate to Plate" site regarding reactive speaker load emulation, you'll conclude that it seems to be designed poorly in the sense that it doesn't seem to be providing a correct emulation (weird resonant) point, plus it lacks some resistors to limit high frequency impedance rise which apparently contributes to buzziness and increases chance of instability so modding would consist of just adding the Rs or also changing some of the circuit values as well. There was also a Swedish guy who goes by "Ralle" on some of the amp-centric forums using one with which he shorted out the LC pair entirely, stuck some series R with his brake, mismatched so the whole PB+R load was higher than normal with his marshall SL and sounded quite nice doing some Van Halen stuff.

[petemoore]

  Dern things are expensive, the 'good' ones anyway.
  And 'good' isn't...IMO...adding a buncha resistances and cables and jacks and other points of failure to an output section...ok, as long as you know...or to be avoided for best long term results.
  Going to all the trouble to produce power, then turn that into heat isn't an effecient way to run the amp or heat the house...I like getting every bit of mileage from Tubes, attenuators turn 'sound mileage' into 'heater output'..
   And shopping around for a nice little tube amp for little applications is recommended. 15w is Loud !, I could use smaller yet

[Dai H.]

I agree that if you have the money, space, etc. it's better to buy more amps sized to the situation you're going to use them in. The basic Marshall problem I guess. You turn it up to get good distortion then you end up with too much volume.

[Johan]

I agree that if you have the money, space, etc. it's better to buy more amps sized to the situation you're going to use them in. The basic Marshall problem I guess. You turn it up to get good distortion then you end up with too much volume.

...yes, the easy part, if you have lots of money and someone to carry them all, is to bring amp's of ALL sizes and select the one that is JUST loud enough for the venue you're playing ...me, I bring a Marshall and a powerbreak, then turn it down...
...seriously thou...the powerbreak sounds good, but a big part of the marshall sound is the speakers working hard, so you either live with it or try to compensate...
if you run a smaller amp ( <50w ) there are pot-style L-pads you can buy..but again same problem..turn down too much and the tone changes a lot...
...but then thats why we are all here..the search for the perfect tone at all volumelevels goes on and on and on and on and........

johan

[petemoore]

  I don't think there's a 'replacement' for a tube amp, 'loaded' [loaded means cranked and being pushed], into speaker[s in the sweet zone of their output volume.
  The volume range isn't really that big on any system like this.
  To get the tube amp 'growl', I mean output tube distortion, you wont' be getting a big, loud, clean, 'spanky' sound...it growls instead...you'll need alot more headroom...it's setup to growl when pushed.
  Then if you have sufficient headroom for clean spank @ whatever volume..well..that isn't going to growl one bit 'till Alot More Volume is added...a dirtbox or some other form of 'pre-dirt' is what you'll be needing to get any 'growl' or TA distortion...
  Power brake certainly will 'widen' the range of volumes with 'X' dirtlevel [output dirt] settings, and so it makes sense...when the alternative is probably only a little different...dragging out the right sized TA/Speaker setup for the application.
  I'm using 15w and a 12'' or two, then another set like that, then a Mic>PA for 'low volume', med volume, and stage sound/w PA supplement.
  50w and a PB would probably work ~differently and very well, I'm just very scrutinizing of 'non-fault' about output section continuity, shiny amp jacks/cables/speaker jacks/everything else soldered...I've encountered, and seen others cry over tube amp failure/damage when output continuity had been compromised, now I'm shy about anything except excellent continuity in a system where ohmage match has been confirmed.

[Dai H.]

yeah, extra protection might be desirable like those diodes on the plates or something for possible open condition such as a fixed R across the outputs and whatever else works well. I've thought about running the heaters separate from the B+ and turning down with a Variac. Certainly not a unique idea, but less volume and less stress on the amp, bit less power consumption seem to make it appealing. What would really be nice is a sound proof basement. 

[petemoore]

  I used to punish my amp for shouting so loud, I would make it stand facing the corner for the whole night.