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One Tube Amp Build Underway

I have successfully prototyped the One Tube Cigar Box Amplifier shown in the Free Plans section. I added two modifications. One for safety and one for guitar and microphone use. The amp must be used with a preamp of some sort in order to drive the amp to full output. With 3.5 volts RMS input I measured about .7 watts output power. The amp is not quite as loud as a LM386 chip amp. Overall, considering its crude design, the amp sounded pretty good. It has some hum that probably cant be avoided. When using a small speaker the hum is not that noticeable. I am also going to build a version of this amp using a 117N7 tube which should get me closer to 1.2 watts output and can also handle a little hotter input level. The parts count is below 20 for amp and preamp and it should be very easy to build for people familiar with basic tube amp construction. Voltages in this amp are around 120VAC and 120VDC so caution must be taken to prevent electrical shock while building and working on this amp. I will try to put together a complete schematic and build notes as I get time. I plan on mounting everything, including speaker, in a single cigar box. A true cigar box tube combo amp !

Required mods are as follows.

1. Add isolation transformer for safety.

2. Added this preamp http://www.till.com/articles/GuitarPreamp/

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Replies to This Discussion

Permalink Reply by petey twofinger on March 30, 2011 at 5:03am

man that is too cool !

are you going to do a video , please ?

Permalink Reply by BLY on March 31, 2011 at 2:14am

Probably just some pictures and audio samples once I get the amp built and looking presentable. Right now I am in the tweaking phase. I have the amp sounding pretty good with a respectable volume level. Getting it all to fit in one box is my next challenge.

I am also going to build an amp of my own design using one 12FX5 power tube. The advantages of this tube is it's tiny size, higher gain factor, less hum and a bit more (1.3W) power. I think this will be the way to go.

Permalink Reply by petey twofinger on March 31, 2011 at 3:00pm

excellent , please keep us posted ,

i would be really interested in making one for myself .

the 5 mini amps i made are kinda cool , but a lil tube amp , thats the tops !

Permalink Reply by BLY on April 5, 2011 at 1:18am

Update - Started to layout the chassis and box last night. Everything fits! Mounted the tubes and power transformers last night. I think I am going to use a tube preamp instead of solid state. Easier to mount and wire another tube than it is to build a J-FET preamp module and find room to mount it. I can also get a whole lot more gain from the tube preamp. So now it will be a two tube amp. Will have to see how well that works out. I should have the amp built and working by the weekend.

Also working on a higher (3 Watts) power amp design using a single ECL85 tube. This tube is two tubes in one. Both a preamp and power amp.

Stay tuned...... Schematics, Pictures, Sound Clips to follow.

Permalink Reply by BLY on April 6, 2011 at 12:30pm

Some pics on my "One Puff" all tube cigar box combo amp. Two tubes ( 117N7power tube, 12AX7preamp tube), one watt, 4 inch speaker. Sounds great ! Schematic and sound files to follow.

Permalink Reply by BLY on April 6, 2011 at 12:38pm

Have to resize the pics first.

Permalink Reply by BLY on April 6, 2011 at 12:49pm

Some pics on my "One Puff" all tube cigar box combo amp. Two tubes ( 117N7power tube, 12AX7preamp tube), one watt, 4 inch speaker. Sounds great ! Schematic and sound files to follow.

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