ldk
Joined: Nov 08, 2017
Posts: 367
San Francisco Bay Area
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Posted on Dec 09 2023 07:42 PM
I've been interested in vacuum tubes since I first started playing guitar in 2013. I first studied how tubes worked, refurbished some old tube record players, and made a few guitar amps.
Along the way, I picked up some tubes from my dad's house. These were for a radio for a '57 Ford Thunderbird that he was rebuilding. These run on 12 volts, so there's no danger of killing yourself when working with these tubes.
In my playing with these, I found that they make a poor amp, but I had good luck making a boost pedal. I ended up making a pedal with a 12AE7, which is a dual triode tube. See the schematic below. It boosts the voltage of guitar input nicely, from about 0.08V to about 1.4V when the gain is maxed. To my ears, the 12AE7 tube sounds good going into a 6G15-like reverb and then into a 6V6 push-pull amp.
In case anyone is interested in figuring tubes out, these make a nice, safe introduction with a usable product at the end.
Here is a picture of my pedal, which also has a 12AL8 tube, which is a triode-tetrode combo. The gain is less, but it's all clean. 12AE7 tubes can be had on eBay for about $15.
— If I'd stop buying old guitars to fix, I might actually learn to play.
Bringing instruments back to life since 2013.
Last edited: Dec 09, 2023 19:44:01
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synchro
Joined: Feb 02, 2008
Posts: 4446
Not One-Sawn, but Two-Sawn . . . AZ.
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Posted on Dec 09 2023 10:43 PM
Very cool.
— The artist formerly known as: Synchro
When Surf Guitar is outlawed only outlaws will play Surf Guitar.
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edwardsand
Joined: Jun 29, 2018
Posts: 757
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Posted on Dec 10 2023 10:40 AM
I was just wondering about whether it was easy to build preamp or boost pedals using tubes, and now you've provided the answer. What does the 12AL8 do in the circuit?
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ldk
Joined: Nov 08, 2017
Posts: 367
San Francisco Bay Area
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Posted on Dec 10 2023 01:38 PM
The 12AL8 is hooked up in parallel with the 12AE7. The 12AL8 boosts 0.08V to about 0.5V and the wave form is bigger, but not distorted. With the 12AE7, the wave form is rounded on one side or both depending on the gain. I haven't explored what happens when the tubes run in parallel, but that works, too.
I have a schematic, but it's not up to date. I'd have to look inside the pedal to update it, but if anyone is interested, I'll do that and post it. Just for fun, here's a pic of the inside.
— If I'd stop buying old guitars to fix, I might actually learn to play.
Bringing instruments back to life since 2013.
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DeathTide
Joined: Apr 13, 2018
Posts: 1374
New Orleans
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Posted on Dec 11 2023 03:14 PM
That is AWESOME!!!!! I would love to see your schematic and I'd appreciate the layout too.
— Daniel Deathtide
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edwardsand
Joined: Jun 29, 2018
Posts: 757
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Posted on Dec 11 2023 03:37 PM
Yes, I'd like to see a schematic as well.
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ldk
Joined: Nov 08, 2017
Posts: 367
San Francisco Bay Area
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Posted on Dec 11 2023 09:50 PM
Here's the layout. I don't have a schematic, but I hope if you need one you can construct it from the layout.
— If I'd stop buying old guitars to fix, I might actually learn to play.
Bringing instruments back to life since 2013.
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Ben
Joined: Feb 11, 2007
Posts: 591
Encinitas, Ca
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Posted on Dec 12 2023 08:19 AM
Very cool project…  I dig the copper box too!!!
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ldk
Joined: Nov 08, 2017
Posts: 367
San Francisco Bay Area
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Posted on Dec 12 2023 08:21 PM
Ben wrote:
Very cool project… I dig the copper box too!!!
Thanks! 10 years ago I bought a roll of copper sheet, thinking I'd make some garden critters. I made a gecko, but that was it.
I also used the copper for a 6G15-like reverb: https://surfguitar101.com/forums/topic/36024/?page=1#p463188
— If I'd stop buying old guitars to fix, I might actually learn to play.
Bringing instruments back to life since 2013.
Last edited: Dec 12, 2023 20:23:31
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