London Power power scaling kits

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Frank Prince, Jun 23, 2006.


  1. Frank Prince

    Frank Prince Member

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    I don't know a lot about these. Can you build one into your tone-tasty modern amp of choice like a Dr. Z, Carr, etc. to bring the volume down and get "that" tone w/out going deaf? I'd be interested in anyone's experience in installing these in any amp.
     
  2. hw2nw

    hw2nw Member

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    bump. Me too. Someone help us out!
     
  3. VacuumVoodoo

    VacuumVoodoo Member

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    In a few words, it's basically a high voltage regulator with which you can reduce B+ supply to output tubes combined with a bias voltage shift to bring the tubes to correct operating point at the reduced B+.
    It can be installed in most amplifiers with fixed bias, I'm not sure about cathode autobiased amps. I have not worked with power scaling myself but
    Jan Jonsson, a friend of mine, has made a series of clips with blackface'd and power scale'd Fender '78 Vibrolux Reverb, his website: http://www.vintage-vibe.net/, click on "soundclips" and scroll to the bottom of page.

    I think Kevin pops in here from time to time so he might chime in.
     
  4. TheAmpNerd

    TheAmpNerd Member

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    It is not a simple as Kevin would have you believe
    to retro fit into existing amps.

    I'm sure there are a lot of problems that had to
    be worked out too, as the whole volume (in his
    TUT series) was delayed more then a year.

    I have not installed one (kit), nor have I purchased
    the $100+ book which is supposed to reveal
    all there is to know about it.

    From what I have read on the net from a guy or two
    that tried installing it/them, it appeared as though (the net authors
    writing, not mine) they thought it was the first time
    through for that amp to be fitted with a kit and
    Kevin had to solve problems.

    I might add it is always simpler to be the critic then
    the guy in the trenches trying to make it work.

    Generally, Kevin is a pretty good writer and has a good brain
    so he'll probably work through the problems as they present
    themselves. Anyone buy his power scaling book?

    Give one a try and let us know what you find out.

     
  5. TheAmpNerd

    TheAmpNerd Member

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    UPDATE:

    Went to the website and found the following:
    You can get the PSK (power supply kit 1, 1w/board, 2) $132, $142, $90.
    and the BMK (bias mod kit) $23 - $71.
    PSB (power supply boost) $128.
    There is also the PS-B (power scaling box) $200.
    Don't forget switching from TUT2 (the ultimate tone vol 2) $46.
    TBS (tracking bias supply) $42.
    CCK (circuit card kit [includes free Sharpie : ]) $47.
    THS (tracking hi-voltage supply is coming soon).
    PMS (need I say more?) $10.

    Perhaps we should just request the following:
    WBOW (whole ball of wax) for $799 installed.


    Opps, TUT4 (power scaling) is still back into production again.
    it used to be $100.
    This makes two years running after an early release (I think last year),
    it also confirms in my mind, that power scaling isn't as simple as first thought.
    More bugs need to be worked out.
    Also with all the parts and kits...your guess is as good as mine as to
    what you would really need.

    Read all about them here:
    http://www.londonpower.com/kits/psbox.htm

    and here:

    http://www.londonpower.com/books.htm

    and here:

    http://www.londonpower.com/kits/psk.htm

    In all fairness though, all these kits, parts, etc
    are extremely problematic especially for the novice.
    AND
    If you have a peice of vintage gear, well don't
    ruin it or its value by sticking one of these
    kits in it.

    Moral of the story?

    Buy the amp that is right for you.
    Different venues may require different amps.
    No one amp can do it all.
     
  6. Amptone

    Amptone Member

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    After reading about a power scaling mod project, I concluded that power scaling or the sag circuit is not something to retrofit in as a kit -- except for a few people to do as pure research and proof-of-concept, but rather, power scaling is something that needs to be designed into all amps prior to manufacture.

    If you are an advanced tube circuit builder, you may find it good to experiment with a power scaling retrofit. If you are a DIY or pro amp designer, you'll find it definitely worthwhile to design power scaling into new amp designs or rework an existing amp design to construct future units.

    If you are not in those categories, but want to obtain power scaling in an amp, do not mod your amp or have it modded unless the manufacturer has already designed the retrofit and will implement it in your amp -- instead, purchase an amp that already has power scaling integrated into its design. There are several now; some are listed at my site and we should hope that power scaling (power attenuation that sounds good down to the 10 mW level) will very soon become standard in all amps. Supporting manufacturers who have already gotten on board with power scaling, by purchasing ready-made amps from them, will help the industry more than a few people doing a DIY retrofit. The vision: go into the guitar store and see no solid-state toy kids' beginner amps for wannabe's, but instead, look around and see that all guitar amps have built-in power attenuation -- not from 100 watts down to 60 watts, but rather, 5-50 watt amps with attenuation that is designed to sound good down to a few milliwatts.

    -- Michael Hoffman, Amptone.com
     
  7. 56_Special

    56_Special Member

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    I had a LP Power Scaling Box ($250) installed into my Ceriatone 18 watt Marshall clone. My amp tech charged me $75 to do it. It works amazingly well, just like advertised. There is no reason not to retrofit it into an amp unless it is vintage and thus should be kept stock. By the way, my amp is cathode biased. Anyone interested in having almost complete control of their amp's volume while retaining nearly every nuance of their cranked amp's tone should consider it.
     
  8. TheAmpNerd

    TheAmpNerd Member

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    Mtlin,

    Sounds like a winner.
    Wondering is that another PS-B?
    The last one listed I thought was only $200.
    What else was installed?


    It helps that your amp tech is Kevin himself, I presume?


    Michael,

    That is what I was kind of thinking also. Not that I've gone and done it.
    Though the amps appear to have been designed around power scaling.

    Thanks for your thoughts.
     
  9. Amptone

    Amptone Member

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    mtlin, was your amp tech Kevin O'Connor, the designer of the Power Scaling box?

    http://www.londonpower.com/links.htm
    lists authorized installers of Power Scaling (8 of them, at the time of this post)
     
  10. Amptone

    Amptone Member

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    It's unclear how find a Power Scaling amp to demo. One would have to make a number of phone calls and send a number of emails. Buying it and optionally returning it is not a demo.
     
  11. TheAmpNerd

    TheAmpNerd Member

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    Michael,

    There are a bunch of uncertainties and many things that need
    to be clarified with this power scaling. For some reason being south
    of the boarder there aren't many folks doing it save for Mojave.

    I've neither read nor seen any type patent or licensing
    info about power scaling until I posted my query to TGP.
    Somewhere here or over in Amps and Cabs.

    A short time later (within two weeks) I saw for the first time that someone
    posted that they were an officially liscensed power scale shop...
    ...or something to that effect.

    I'm going to bite the bullet and install one into a hacked
    Hiwatt Custom 50 head that has been sitting around here.
    Along with new trannies, chassis doubler for the PT
    and installing a PSK or PSB.

    It will be a nice thing to document too.
     
  12. Amptone

    Amptone Member

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  13. Bainzy

    Bainzy Member

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    If you just install the PS-Box it's a simple 30 minute installation, and sounds killer. It gets more complicated the more things you want to do with the amp (variable sag, additional output tube drive), but if you just want amp on 10 tone at small club levels it will do it easily and better than any attenuator I've heard.

    The problems I ran into were:

    cooling - it's a 100w amp, so I added thermal grease to the MOSFET and a fan powered by the PS-Box, not really hard to fix

    signal level too large - I only scaled the output tubes so they distorted too early, and there wasn't much play on the DC pot. solved by scaling the PI too, but could've been avoided from the start.

    scaling the PI - doing this means you can't slam the output tubes independently of the PI, so I fixed this by adding more variable resistance between the voltage dropper resistors and the PI's 82k/100k resistors, separately of the preamp though of course.


    Now that I've solved all these issues though, anyone who has seen this post or seen my threads on Metroamp could fix these problems at the same time as installing a PS-Box so it wouldn't change the installation time past 30 minutes.
     

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