Plug In Voltage Meter

Discussion in 'Shock Brother's DIY Amps' started by jchabalk, Jul 30, 2019.

  1. Milspec

    Milspec Poster Extraordinaire Silver Supporter

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    I would really like to ask why? The bucking transformer lowers the voltage by a percentage placing your effective voltage in a lower range, but the variac will allow you a more specific setting according to the amp design. I just don't see the benefit over the variac except maybe in weight. If someone mistakingly turned off the bucking transformer you would jump back to what-ever voltage was present at the wall outlet. If someone mistakingly moved the variac dial to 100%, you would also just end up with the same wall voltage.

    So, what am I missing here?
     
  2. Milspec

    Milspec Poster Extraordinaire Silver Supporter

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    That is what I have planned as well and have been using those little votage readers for years...really useful and cheap item.
     
  3. schmee

    schmee Doctor of Teleocity Silver Supporter

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    Well, it depends on the amp, but my 65 BFDR and 65 BFD run 460-465 volts on the power tube plates at ~121 wall voltage. The last set of RCA NOS 6V6's I bought lasted half a gig and took out the vintage output transformer. Maybe that's why?
    I'e had many BFDR's, 10 years ago I had 4 at the same time. They all were that way.
     
  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    "So, what am I missing here?"

    The weight of the variac vs the bucking transformer. My bucking transformer design gives -7 or -12% voltage and works fine for me.

    [​IMG]
     
    D'tar and King Fan like this.
  5. King Fan

    King Fan Poster Extraordinaire

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    Rob, I've been highly tempted to build one of your bucking transformers. Elegant and simple. Plus I was hoping cost would be an advantage over a variac, but maybe not. I'm having trouble finding your suggested Hammond 166N12B for less than ~$25 plus shipping. You note this cost you $14 -- d'you have a secret source?

    For those asking why? I once read a massive article in an old EE journal about increasing tube life; their simplest and strongest recommendation was to never run heaters above spec voltage. This is before considerations that vintage B+ and plate voltages may sound better in vintage amps.
     
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