Voltage Reducer To Play Youre Amp Through

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113
A friend loaned me a outlet box with a transformer mounted in it to reduce wall voltage -6V or -12V. Very interesting difference when I play my 1962 Fender Pro amp with this unit. Are these commonly available and I just missed this? Has anyone else used one of these?
Thanks John
 

Kyle B

Member
Messages
5,290
Wall voltages have risen since '62. By dialing back the wall voltage, you're actually getting closer to original.

I haven't seen one of these commercially produced, but they're easy to build if you wanna make one.
 

zenas

Member
Messages
8,871
It's called a bucking transformer. (if I remember right) There should be plans online, not really to complicated, but like a light bulb limiter it can get that way.
I'd check the bias with the lower voltage.
 

UsableThought

Member
Messages
1,649
Only $350. What a bargain!
The selling point seems to be the versatility - a choice of 4 possible mains AC voltages, plus four different percentages after that for reducing the selected voltage: https://www.amprx.net/product.html

By comparison, as I'm sure you know, a typical "build your own" bucker is going to have only 2 choices for percent reduction, and a fixed approximation (made by the builder) as to the expected mains voltage. So it's fine for use at a known single location (e.g. at home), but might not be so handy for gigging at different venues.

I'm sure someone who wanted to could whip up a DIY recipe for a much more versatile bucker, on the level of this BrownBox . . . but at some point the materials cost is going to add up & make it less attractive. E.g. I know that for pedals, DIY builds typically end up costing more than if you bought the equivalent circuit at retail price - mostly it's the shipping costs that eventually get you. And few of us hobbyists are going to buy in bulk. So we build pedals for fun (and aggravation), rather than to save $$.

P.S. @powerwagonjohn - there are plenty of old threads on this forum, and on other forums, with links to recipes for building your own "vintage bucker". The two most used recipes are one at the GeoFex web site and another at Rob Robinette's web site. Here's an old thread on this topic that has links to both - https://www.thegearpage.net/board/i...step-down-voltage-reducer-for-my-amp.1918643/
 
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zenas

Member
Messages
8,871
There's always the veriac option. That can be problematic because the dial can get turned and the good old units weight as much as a 440 Chrysler block.
But if you use one and check it's output voltage every time it should work, suck for gigging though.
I messed with mine and a few amps when I got it but really haven't used it since.
 

PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,139
There's always the veriac option. That can be problematic because the dial can get turned and the good old units weight as much as a 440 Chrysler block.
But if you use one and check it's output voltage every time it should work, suck for gigging though.
I messed with mine and a few amps when I got it but really haven't used it since.
Much cheaper than the "brown box" thingy, too.

Just put a meter on it, because what the mechanical knob says and the actual output is never the same.
 

UsableThought

Member
Messages
1,649
But if you use one and check it's output voltage every time it should work, suck for gigging though
R.G. Keen's somewhat caustic opinion on this option:

Variacs are one way to correct this, but these things are huge, heavy, and carry the temptation to twiddle the voltage just a - little - bit more to see what it would sound like. I looked up variacs in a Mouser Electronics catalog now. It's capable of supplying 3A of AC, weighs about 18lb, costs $68.00, and doesn't include a box to put it in. You'd have to buy a metal box and switches, fuseholder, outlet, and then wire it together, possibly another $15 plus some labor. The cheapest already-boxed up variac they list is a 5A unit. It's ready to use, but weighs even more and costs $188.00.​

Assuming that sounds OK, you're going to pay for and haul around this thing. You set up at a gig, measure the AC line voltage, set the variac to give you 110VAC just like your vintage AC-30 needs, and play a thunderous set. You take a break and while you're away, the bass player takes a gander at your new tone-toy, fiddles with the knob, but sees you coming back and leaps away from it so you won't know he messed with it - and accidentally turns the knob up to the 132V maximum. You don't know he touched it - he gets away scot-free - but when you flick it off standby and start into the new set, the amp begins to sound a little funny and some smoke curls delicately out the back...​
 
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PLX

MENSA member, Astronaut, Dated Your Mom Once
Messages
15,139
R.G. Keen's somewhat caustic opinion on this option:

Variacs are one way to correct this, but these things are huge, heavy, and carry the temptation to twiddle the voltage just a - little - bit more to see what it would sound like. I looked up variacs in a Mouser Electronics catalog now. It's capable of supplying 3A of AC, weighs about 18lb, costs $68.00, and doesn't include a box to put it in. You'd have to buy a metal box and switches, fuseholder, outlet, and then wire it together, possibly another $15 plus some labor. The cheapest already-boxed up variac they list is a 5A unit. It's ready to use, but weighs even more and costs $188.00.​

Assuming that sounds OK, you're going to pay for and haul around this thing. You set up at a gig, measure the AC line voltage, set the variac to give you 110VAC just like your vintage AC-30 needs, and play a thunderous set. You take a break and while you're away, the bass player takes a gander at your new tone-toy, fiddles with the knob, but sees you coming back and leaps away from it so you won't know he messed with it - and accidentally turns the knob up to the 132V maximum. You don't know he touched it - he gets away scot-free - but when you flick it off standby and start into the new set, the amp begins to sound a little funny and some smoke curls delicately out the back...​
Bass player ?

You mean the drummer, right ?

:p
 

jbltwin1

Member
Messages
278
Actually built the bucker for my 71 bassman head just as a hedge against crazy high line voltages that we ran into sometimes. Really made the sound different running it closer to it's INTENDED voltage. HMMM? Wonder where I put that?
 

HotBluePlates

Member
Messages
13,903
A friend loaned me a outlet box with a transformer mounted in it to reduce wall voltage -6V or -12V. ... Are these commonly available and I just missed this? ...
... I haven't seen one of these commercially produced, but they're easy to build if you wanna make one.
I remember a commercially produced device that does similar voltage drop. Brown Box:

https://www.sweetwater.com/store/de...wnbox-tube-amplifier-input-voltage-attenuator
It's called a bucking transformer. (if I remember right) There should be plans online, not really to complicated ...

Apparently Guitar Player tested the Brown Box and another line voltage reduction device a couple years ago. When evaluating the cost/performance ratio of these devices, it's very much worth considering how they accomplish the goal of "reduced voltage."

Brown Box:
I haven't seen a photo of the innards of this device (apparently no owners have chosen to open it up & spill the beans). However, speculating based on the available knob positions this appears to simply be a transformer with 4 primary taps and 5 secondary taps. The "Bypass" position would simply be a 1:1 turns ratio from primary to secondary, while the "3%" position is a 1:0.97 turns ratio, "6%" is a 1:0.94 turns ratio, "10%" is a 1:0.9 turns ratio, etc.

If I'm right and there's a PT inside, at least there is some isolation from wall outlet to amp and a big lump of iron to justify the price (yes, there's also a meter & switches though these aren't terribly expensive to add).

GeoFX Vintage Voltage:
This is the original bucking transformer plan presented by R.G. Keen over 20 years ago. It uses a simple 6v/12v (probably 6.3v/12.6v) transformer to buck wall voltage by one or two preset amounts. These are cheap to build, but do not provide the same degree of isolation as the transformer I assumed AmpRX to use in the Brown Box. If the P3 Line Tamer included in that Guitar Player test above uses this bucking transformer plan, the $295 price tag is just about unconscionable (but most players can't make their own gear, so...). Again, the LCD meter is handy but an inexpensive toy to add on to what's otherwise a maybe simple device. Oddly, P3 keeps this product on their website but says it's "Sold Out."

The transformer used for bucking line voltage could be quite a bit smaller than that in the Brown Box.

Variac:
"Variac" was since 1934 a General Radio trade name for a variable autotransformer; other companies made variable autotransformers, but the common term became "variac" just like "Kleenex" is a common term for facial tissue paper. Rather than bucking (using an opposite-polarity voltage to counter & reduce the wall voltage), an autotransformer simply selects a different tap along one big coil of wire to change the wall voltage to some other voltage (lower and/or higher than the wall voltage). It doesn't have any isolation from the wall outlet, so it's less-safe than a true transformer; being a single coil of wire it should also be cheaper (though the movable brush in a variable autotransformer raises the price).

If you're patient and buy used (from a source that's not specific to guitarists & guitar amps), these can be found inexpensively. I got mine from a "seller" who only charged me the ~$12 it cost to be shipped to me in a flat-rate box.


Bottom Line:
Someone with the time & capability/ingenuity to make their own voltage-reduction device should only have to spend $50-60; someone buying used from a hamfest or local seller could probably find something for even less. The $300-400 price tags on some of the things out there seem obscene to me, but then I remind myself not every potential user can "roll their own."
 
Messages
113
The one my friend loaned to me has only two choices -6 and -12. this will work great for me as I usually only play at home or my buddies studio. I think I will look into building my own using my friend's design with the Hammond transformer and an outlet box. looks real easy to do. Now that you guys mention a bucking transformer I do remember reading about these but that was before I owned the 1962 Pro. I will have to try it out on my other older amps, 67 Bassman, 64 Tremolux and 66 Ampeg Gemini. My other amps are newer and probably don't need this transformer. I am surprised that there is such a difference in tone with my Pro.
Thanks John
 
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Bob Arbogast

Gold Supporting Member
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1,179
I don't see the need for a unit with so many primary and secondary options. I would think that two options would be plenty. Is the mains voltage a little high? Use the -6V option. Is the mains voltage more than a little high? Use the -12V option. Do we really need to be more precise than that? It's not as though a vintage (or vintage-style) tube guitar amp is a high precision device. I can't imagine worrying about 112V vs. 110V.

I wonder, too, about using a multi-turn pot for setting output stage bias. Seriously? Set it for precisely 31.6mA of cathode current, and it will stay 31.6 for how long??? Setting a single-turn pot for about 30mA or about 32mA seems close enough!

That's my sense of things anyway.
 




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