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Permalink Reply by BLY on November 6, 2009 at 9:42am

Yes, This is a very unsafe amp. All you have to do is touch another piece of gear while holding your CBG and get full 115 VAC mains current across your heart. Probably kill you !

You need to install an 1:1 isolation transformer on the AC power input. Then connect a 3 wire power cord with ground. You can get transformer from Antique Radio Supply or similar. Any amp tech can help you.

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Permalink Reply by Gobi on November 6, 2009 at 10:19am

Yes this one. Because you HAVE TO get in contact with the ground on an electric guitar this really not to recomand!
The name Cigar Box amplifier is just because of the verry small size (in these days)

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Permalink Reply by Gobi on November 6, 2009 at 10:22am

...and it's not "potentially dangerous " - in my poit of few its ABSOLUTELY DANGEROS

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Permalink Reply by Tim on November 6, 2009 at 10:35am

if you want a small amp just do a search for "firefly guitar amp" it runs a solid state rectifer and 2 12a?7's

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Permalink Reply by StarGeezers on November 7, 2009 at 1:36am

What tubes do you have in that amp ???

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Permalink Reply by Michael Estep on February 9, 2017 at 7:21am

I was checking out the schematic from the one-tube amp that was posted here http://www.guitarworld.com/diy-musician-build-your-own-one-tube-amp... and have a few question. In the explaination of the build the writer says to add a .05mfd 200V Cap in the position shown on the schematic by an X. Will doing what is highlighted (in the attached picture) along with adding a grounded plug to the amp prevent electrical shock? Is this a way around the Isolation transformer? Or what exactly where they trying to do with adding this cap?

Attachments:

• image.png, 105 KB
• image(1).png, 283 KB

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Permalink Reply by Timothy Hunter on February 9, 2017 at 10:38pm

there are plenty of safe amps out on the internet to make. this looks very dangerousAC mains direct to the heater element of the valve.

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Permalink Reply by Regan on February 11, 2017 at 9:34pm

No, there is no way around an isolation transformer in this amp.

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Permalink Reply by David L. on February 12, 2017 at 1:20am

Whilst not being an amplifier, for a first time introduction to valves I like the Matsumin's valvecaster boost pedal - low parts count and if you wish you can wire it direct to the valve. Best of all the circuit uses a 9v supply so no worries about the high voltage normally needed for valve projects. If you use it as a boost pedal between your guitar and amplifier it adds a valve sound to a solid state amp.

http://miaudio.com/wordpress/wp-content/uploads/2013/11/12AU7-6111_...

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Permalink Reply by Timothy Hunter on February 13, 2017 at 1:26am

thanks for the link David. what a nice simple circuit.  might have to rethink the preamp in my amp rebuild...  

have you built one? and if so does it have a nice crunch tone?

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Permalink Reply by Paul Craig on February 12, 2017 at 9:26am

You have to know what your doing with tube amps. The tubes can produce 300 to 400 volts that can stop your heart very quickly. Read up on tube amps circuity before building anything with a tube in it.

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