how to make a guitar amp from an old transistor radio
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Michael. Wow I haven't been on here for a few years. I'll try answer a few questions. You should be safe using the radio with AC as long as you have done the mod correctly but only work on it with battery power. Sounds obvious but poking around inside it should never be done while plugged into mains. No you can't wire the jack to the two way pot. Basically a radio circuit is based on two "stages". The tuning stage takes the radio signal and converts it to something we can hear. The amplifier stage well err amplifies it. The two way pot is in the tuning stage and you want to hack into the input of the amplifier stage which can be found on the volume pot. You could still keep the whole radio receiver side working if you wire a changeover switch into your hack to switch between guitar input or radio. Cut the existing wire from tuner to volume pot then wire the middle tag to the volume pot , one end tag to guitar jack and the other end to the wire coming from the tuner. Sorry no idea what an Artec Psychknob is but it sounds interesting. Hope this helps.
I don't know if you or anyone check comments to this old thread, and I'm about to search to see if there's more recent threads about this sort of hack. Where people have done these things.
But I have a couple questions. I found a great 1970 Sears Roebuck radio today for 7 bucks and I want to use it for a cigar box guitar amp. If you have a radio that takes batteries AND can be plugged in, is it safe to use with AC, or do I have to use it only with batteries? I can't get a clear answer, most of the people who post these things say no, but they also say they no nothing about electricity and radios, so I don't know how accurate it is. Also If I have a dual band Am/FM radio, can I wire the jack into the two way pot instead of the volume knob, that way let's say I could keep the am band and swtich the pot to the fm side for the guitar (actually what I'm considering doing is putting in a mini computer audio jack so I can use it as speaker for my computer or headphone jack on my phone.) I'm also considering swapping out the tuning knob with an Artec Psychknob effects board/pot. I'm wondering if that would work and if I'd run into trouble with powering it, especially if the amp could work plugged in. Any thoughts?
This is the radio I got today.
http://www.radiomuseum.org/r/sears_roeb_portable_dual_power_2035_ja...
You're very welcome Mike. What I'm going to do with this small "cracker box" amp circuit I've outlined here is put it inside a cigar box guitar I've started building. Self amplified CGB. I've got some tiny round magnets from my wife to make my own pickups out of, they're very strong. She uses them inside her small art work pieces. I'll wrap them with the wire from the small transformers I removed from the radio. I think my CBG will sound better with this than the peizzo pickup. I'll post some pics as I go....Wayne
Thanks for the pointers Wayne. I finally had some success. What I'm learning, which I'm sure all who have walked before me have done so as well, is that not all radios are the same and some are VERY different than others so each conversion can be a unique process. Anyway, I've converted a small vintage Kmart radio and an old Silvertone and they both were extremely different but both sound amazing. Still much to learn before I can offer any tutorials myself but I hope to get there...like you said it's addictive and I'm looking for my next mod...
Mike
Mike
Mike
If you watch the video closely you'll see I am pointing to where the volume pot and the detector diode is situated and showing you how to find the correct point where the jack needs to connect using the signal generator. Each radio is different so unless you have one exactly like this radio, there is no point showing it in extreme detail. The idea of the vid was meant more for inspiration and imparting a little bit of knowledge for you to find the correct point on your own radio. Basically connect the outer of the jack to ground (usually the biggest piece of the printed circuit which will also go to one side of the battery, then the inner of the jack to one of the pot lugs. Experiment by turning the vol pot up and down while someone plays your guitar until you find the lug that works correctly.
Go to this place, http://makezine.com/ and search for cracker box amp. and you can find a pretty good step by step. I've done it twice, and it sounds killer good. Especially if you use a stomp box too.
All these videos I've watched that say "how to" and not a single person shows in detail where each wire goes. You talked about what you did in general but then it's all put together and that's it. Could someone out there with competence show visually where each wire goes ie "I solderd the wire on the ring of the input jack to this point on the volume pot and the tip of the input jack to this point on the volume pot" etc and SHOW IT.
I tried each wire from the volume control pot, from left to right they are brown,green,and red wires. Radio is on and is loud and clear. First was the green, when clipped the radio went silent, connect to guitar and nothing, connect guitar to circuit board and heard both. When I tried the brown wire it worked but the volume control was not working and radio and guitar could be heard. When I clipped the red it went silent and guitar could be heard through pot when connected. Grounded onto metal plate holding control knobs, and central wire to red leading to volume control pot. When the cbg is connected to my big guitar amp I have to really crank up the volume to hear it. I think the piezo in there is the problem....Thanks smojo, great video, very clear instructions compared to others I looked at.
Timothy - sounds like you either got something not quite right with your wiring or the radio was faulty to start with. Did you try it as a radio first and did it sound loud and clear? If it was OK then double check how you've got it wired. They can sound crap with piezo's and OK with mag pups which is down to impedance mismatch but it should sound better than you described.
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