Poor mans variac

[ronh]

I have an old amp with PT primary rated at 115Vac. Amp consumes 35W.
Can I use a light dimmer as a variac to lower my AC supply (122Vac) down to 115Vac? I know noise may be a problem, thought I would use one of those filtered power bars. Thanks for ay ideas.

[Enzo]

No. The light dimmer chops out parts of the waveform, so you have something not remotely a sine wave anymore going into the transformer. That will be more than a powr strip can clean up. Besides, those few volts are nothing to worry about. the B+ and what not inside the circuit will be a few volts higher, but that's life.

[Joe Bee]

Hi,
there is a nice trick you can use to lower your mains voltage by a few volts. Just use a wall-wart transformer with its say 5V secondary in series to the mains. If you wire the transformer out of phase, the voltage subtracts from the mains voltage and you are left with 122-5=117VAC. The secondary current of the transformer should be good for what the amp draws, so if that's e.g. 2 amps make sure the wall-wart can supply at least that.

[TD_Madden]

I just ordered one of these from Ted Weber:

https://amptechtools.powweb.com/browner.htm

[black_labb]

would it not be reasonable to us a voice coil from a speaker with no cone. ie, have 1 x ohm speaker and 3 x ohm voice coils, wirring them to get the correct impedance and then running it like that. would that effectively reduce the output by 6 decibels? (decibel level increases by 3 ohms by doubling the no of speakers, so halving it twice (4/2=2, 2/2=1) would give -6 decibels

does running a voice coil with no cone damage it more easily making this just an easy way to blow an ot?

[Bruce / Mission Amps]

I just ordered one of these from Ted Weber:

https://amptechtools.powweb.com/browner.htm

Is there a circuit description?
A few years ago he got a bunch of rheostats and really quite didn't know what to do with them and I suggested he could use them like a line adjustment control in many of my old vintage tube testers.
He wanted to use a bunch of high power diodes to do it.
In other words, is this gadget built with a multi-tapped bucking transformer, a bunch of diodes or a big, variable power resistor?

[TD_Madden]

guess I'll be the guinea-pig and find out!

[Old Tele man]

...is this gadget built with a multi-tapped bucking transformer...?

...that would be the MOST efficient method for sure.

[Regis]

R.G has a page on how to build a vintage voltage adapter:

http://geofex.com/Article_Folders/vintvolt/vintvolt.htm

[ronh]

Thanks for the link to Keen's site. I will try this.

[TD_Madden]

Weber Browner

It seems to work pretty well...my wall voltate is 125vac, using the device dropped to about what my Vox AC50 wanted (115)).

I opened it up...there's a shitload of big diodes in there.....

[Satamax]

Huh guys, just a daft idea which came to my mind. Why not put several 12v lightbulbs paralleled, in series with the amp's AC?

IIRC, you want to use two 110V lightbulbs on 220, you put them in series. Why couldn't that be possible with the amp and lightbulb? We'd need a few paralleled to have the proper curent rating for the amp thought.

Bye.

Max.

[Bruce / Mission Amps]

...
I opened it up...there's a shitload...

Ha ha... sounds about right...

[TD_Madden]

Not sure I know how it works, though.

[Bruce / Mission Amps]

Not sure I know how it works, though.

Have you ever put a big honkin' 600v 10 amp diode in series with your power cord to a light bulb?
They used to be in a little sealed button you stuck under the light bulb to be sold as a power saver.

I don't really know what he is doing in there either but there would be a .6v drop across each diode.
The rotary switch would have to keep piling more in series on the way to it's built in outlet.
Not sure if it is cathode to anode, cathode to cathode or anode to anode for a pair in series, but a string of 10 diodes in series and would exhibit a 6v drop before it got to your amp's power plug.
It would be pulsing DC (which is kind of the definition of AC) so that's why I wonder if they are back to back or anode to cathode.
See if they are wired as pairs and then the pairs in series.

The problem with this is it might goof up the peak to peak voltage ratio and change the amount of apparent power or maybe the VA?
I'll have to try it in a mock up on my bench because I don't have a good answer.
This goes back a couple three years ago but the rheostat idea didn't seem to interest him so I told him he should use a tapped bucking transformer with a rotary switch instead of diodes.... but what do I know?
He's the one with all the money, not me...