Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: g-man on August 30, 2014, 01:45:41 pm
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I don't think it is worth bothering with for guitar amps. And if you're worried about line voltage regulation for digital equipment, a real UPS is much bigger, heavier, costlier, and actually does something worthwhile.
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> keeps it at 120 V +/- 5V
If it is what I think it is.....
It is a many-tap transformer, taps 5V apart. It finds the tap closest to 120V. When that tap rises above 125V or below 115, it *switches* to the next tap.
> usually ~122 VAC but ...currently ...129 V range
Then it will output 122V, until the voltage rises to 126V. Then it will *switch* from 126V to 120V.
If you have 122V from dawn to midnight and 128V midnight to dawn, this may be acceptable. Hard to imagine 129V doing as much damage to a guitar amp as a Furman does to your wallet.
However if you are really getting 129V many hours a day, call your electric company. Say your lamps run real bright and burn-out very quick, and you are "afraid" that the electricity is dangerously high. While "129V" may not get attention, "afraid" usually does. And most residential distribution has regulators (usually step-type like that Furman) which "should" hold semi-steady voltage at the street. Maybe theirs is sticking, or they haven't got your street on a regulator yet.
However I have seen similar systems switch-switch-switch ALL day long every 7 seconds, because the output of one source was right at the switch-point of the following regulator.
I'm curious about Furman's claim of "1 nanosecond". You can't even read the voltage of a 60Hz wave in a milli-Second (a million times slower).
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I'm curious about Furman's claim of "1 nanosecond". You can't even read the voltage of a 60Hz wave in a milli-Second (a million times slower).
"... the new tap is electronically switched exactly at the zero-crossing ..." I assume they're citing the speed of the electronic switching (after the need for switching has been recognized; as you say, no faster than 1/60th second), and letting the uninformed believe whatever they want.
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> letting the uninformed believe whatever they want.
Hmmmmm.
I was going to say (before something better came on TV) that you could slowly make the decision to switch, and then switch with a fast device; and claim that as your switch-time.
However there are not many power devices can switch faster than a micro-Second. Maybe a few hundred nano-Seconds. Nano-Seconds is GigaHertz stuff. Your computer CPU's teeny transistors do that, but not big fat power devices, or certainly not at popular-price for a system which has no huge need for speed.
122 V...129 V.... ya know, a 3% drop makes this 118V-125V, and if that range isn't close-enuff to 120V then you are being fussy. 3% off 120V could be one side of a 6.3VCT winding. I guess if you needed ALL of the Furman's rating it would have to be a 10A-13A rating on 6.3V, which is a pretty big lump.
I'm happy that my power stays in a 125V-110V zone. 125V no-load. My line is so long that the microwave oven sags it about 4V. So far I have not seen any combination of loads that sags even to 110V.
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Here at the plant, we have many applications (120vAC) that have Sola brand transformers (of all sizes, depending on the load requirements downstream). It's been a while since I looked at the nameplate on one, but I believe they maintained a secondary voltage of 120vAC, with a variation of primary voltage of 90vAC to 130vAC. Do a search for this brand. You may find those to suit your needs. I know they last a few decades out here (I'm working this holiday weekend), without a hitch.
Jack
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If built with the switchable option, it is cheaper option, than a variac, or a bucking transformer.
It IS a bucking transformer.
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Those Solas are often available pretty cheap, used. Freight is of course the issue. Try to get one from the 70's, not the 40's (!)