"Hlep" requested w/Amp Electronics

[PsychoCid]

Okay so I'm about to ask a question that 80s metal folks would know. But what's funny to me is, Mickey will know this answer for an entirely different reason.

What size variac do I need to run a 12 watt amp?

12 watts? Or do I need to go higher for safety or something?

Thanks in advance!

[golem]

I'm confused by this question. If you're in the US you'd get one with 120 VAC input. You'll likely blow a fuse in the amp if you put the output too high and I don't think most people would want the output to go lower than 100. Hopefully just a fuse.

[mickey]

I'm confused by this question. If you're in the US you'd get one with 120 VAC input. You'll likely blow a fuse in the amp if you put the output too high and I don't think most people would want the output to go lower than 100. Hopefully just a fuse.

Yep, my DRRI is a 20ish watt amp but to the AC wall socket it is a 100watt load.

The "80's metal" ref is meaningless to me.

[PsychoCid]

Ah okay, thanks fellas.

Looking closer I notice they have multiple ratings. For example it says 120v input, but 10 watt. So is that still too small for 12 watt amp?

With the amp straight into the wall, the volume knob has to stay on 0 to not blow my neighbors away. But if I starve the amps power with a variac, I might be able to push the tubes a lot harder without a big loudness increase. More gain without more volume.

[mozz]

What size variac? Probably the smallest you could buy. They usually start at 400-500 watts. I may have a small one. The 2 I use for tube amp repair are about 1000 watts.

[golem]

I use one of these for what I think you're asking about. https://www.amprx.net/store/p13/2019_Br ... aster.html

It would work for an amp up to 50 watts. It's not a variac but it's much more portable. There's also no way of using it on a setting that would destroy your amp.

[glasshand]

Ah okay, thanks fellas.

Looking closer I notice they have multiple ratings. For example it says 120v input, but 10 watt. So is that still too small for 12 watt amp?

With the amp straight into the wall, the volume knob has to stay on 0 to not blow my neighbors away. But if I starve the amps power with a variac, I might be able to push the tubes a lot harder without a big loudness increase. More gain without more volume.

The watts you see on an amplifier description are the audio output power. That doesn't have anything to do with how much electricity it uses, so don't bother looking at it when trying to choose a variac.

But honestly, why use a variac at all? If the amp is only 12W, use an attenuator, it's a lot cheaper and simpler.
https://guitar.com/guides/essential-gui ... tenuators/

[mozz]

If the watts is written under the voltage, it is the wall watts, not the output. Anyway, if it is a 12 watt transistor amp, it may not even work with a variac, if there's any voltage regulators in there, they drop right out when the input voltage goes below a certain point.

[PsychoCid]

Ooooookay I gotcha. Yes variac would turn down power between wall and amp, so doesn't care about amps output.

Conversely attenuator would cut power between amp and speaker.

Why do I feel like I'd rather starve the amps power than just turn down the speaker? Am I over thinking this? Can't seem to find a good comparison.

[PsychoCid]

So it's still looking like a variac is my best option.

My amp has no fx loop and the plugs to the speaker are the old fork types like televisions from the 70s. So to put an attenuator in would require hard wiring it in.

So now back to looking at variacs...even though they all say 120V, they still comp in different amperages. 5, 10, 20.

Voltage Transformer 5 Amp Auto AC Variable Voltage Regulator,500VAC Max,120VAC Input, 0-120V/130VAC Output

Is this big enough specs for me not to blow up my living room?

[glasshand]

the plugs to the speaker are the old fork types like televisions from the 70s

Can we see a picture of that? I've never seen an amp where the speaker connection wasn't either a 1/4" jack or a speakon jack.

[PsychoCid]

the plugs to the speaker are the old fork types like televisions from the 70s

Can we see a picture of that? I've never seen an amp where the speaker connection wasn't either a 1/4" jack or a speakon jack.

Sure. Hard wired. There are only two cables from the back of the amp. One goes to the built-in pedal. The other goes to the wall socket. That's it!

Fender Champ 12, red knob. IE, not your typical Fender design.

IMG_20200713_174359296.jpg

IMG_20200713_174341980.jpg

IMG_20200713_174335164.jpg

[PsychoCid]

Would love to know how big a variac I need to not lose fingers or toes though. Or at least, not more than one.

[mozz]

1 amp would be enough. But think of it this way, buy bigger and once you get a plexi you'll be set. As i said earlier, a variac may not work with any transistors it may use, channel switching, boost or the reverb.

[PsychoCid]

1 amp would be enough. But think of it this way, buy bigger and once you get a plexi you'll be set. As i said earlier, a variac may not work with any transistors it may use, channel switching, boost or the reverb.

Aha, good point. Being cheap is expensive. Buy quality

Totally hear you on the other features not working. So far I've only done this at small scale with a Friedman BE OD pedal. Turning it down from 9V to 4.5V makes a glorious sound.

The reverb on these champ 12s is almost non-existent even at full crank, and I got a plate reverb pedal for the period sound anyway.

--

Okay, now. Looks like all modern available variacs are made in China. Would I be safer getting a MIC unit with a digital gauge...or like a decades old made in USA general electric unit?

The old USA units cost easily 2-5x what the modern Chinese makes do, even the digital ones.

[Rollin Hand]

Modern ones will have the ability to accept a three-pronged pmud, where an old one might not. That's in part why I sold mine.

[PsychoCid]

Modern ones will have the ability to accept a three-pronged pmud, where an old one might not. That's in part why I sold mine.

YES.

I was looking at some old pieces going, gee if I'm playing with fire should I at least have a decent grounding...

Okay well, I'm still gonna go digital then. The non digital ones can be a lot more than +/- 5% out of spec.

[JimyTheAssassin]

This is the fender champ 12, the one with a single 6L6 output tube right? They have a speaker driven reverb and headphone output. They’re a bit of an oddity in some regards but a cool amp all the same.

Ya I agree with @mozz. A 1 amp or greater would probably be fine. These do exist but you would be searching on eBay for a used unit. I’ve seen as small as 1.25 and 1.75 amp units by Staco that look fairly compact. I’ve also seen 300va Chinese made units that claim 3 amps but if you work the math out at the 130 volts they can work to, it’s really 2.3 amps. The Chinese manufacturers fudge the ratings. If you take a look at the old school variacs; when they say 0-140 at 10 amps, they can handle 1400va.

Here’s an idea for you but make sure you read the listing and agree to the terms. Ymmv.

https://www.ebay.com/itm/333650037646


Sent from my iPhone using Tapatalk

[PsychoCid]

This is the fender champ 12, the one with a single 6L6 output tube right? They have a speaker driven reverb and headphone output. They’re a bit of an oddity in some regards but a cool amp all the same.

Ya I agree with @mozz. A 1 amp or greater would probably be fine. These do exist but you would be searching on eBay for a used unit. I’ve seen as small as 1.25 and 1.75 amp units by Staco that look fairly compact. I’ve also seen 300va Chinese made units that claim 3 amps but if you work the math out at the 130 volts they can work to, it’s really 2.3 amps. The Chinese manufacturers fudge the ratings. If you take a look at the old school variacs; when they say 0-140 at 10 amps, they can handle 1400va.

Here’s an idea for you but make sure you read the listing and agree to the terms. Ymmv.

https://www.ebay.com/itm/333650037646


Sent from my iPhone using Tapatalk

Okay I really like that unit. Have to wonder if it works though. Thank you for the help!

[glasshand]

Sure. Hard wired. There are only two cables from the back of the amp. One goes to the built-in pedal. The other goes to the wall socket. That's it!

Gotcha, thanks! Now that I understand it's hard-wired in, it makes a lot more sense.

[PsychoCid]

Sure. Hard wired. There are only two cables from the back of the amp. One goes to the built-in pedal. The other goes to the wall socket. That's it!

Gotcha, thanks! Now that I understand it's hard-wired in, it makes a lot more sense.

Man that avatar takes me back.

[glasshand]

Man that avatar takes me back.

I have an old t-shirt with the logo too! A guy at a store I went into recognized it and commented once, and we laughed about how you have to be of a certain age to even recognize it.

[PsychoCid]

PS [mention]mickey[/mention] I think this was an appropriate use of electronics rather than electric bits as well. It has mechanical moving pieces, hence the Tron, no?

[Rollin Hand]

Modern ones will have the ability to accept a three-pronged pmud, where an old one might not. That's in part why I sold mine.

YES.

I was looking at some old pieces going, gee if I'm playing with fire should I at least have a decent grounding...

Okay well, I'm still gonna go digital then. The non digital ones can be a lot more than +/- 5% out of spec.

In a semi related note, how in blazes did I type "pmud" instead of "plug?" I really need to read before I hit the submit button.

Of course if someone Googles how to use a variac with a pmud, they'll find this.

[PsychoCid]

Hahaha well I appreciate your help. Found some more key words we can play with!

PMUD
Acronym Definition
PMUD Power Management Utilities Daemon
PMUD Power Management Unit Daemon