Members daklander Posted June 4, 2008 Members Share Posted June 4, 2008 I have an old tube radio that I'd like to use the amplifier section for a small, low power guitar amp. There is no transformer that I can see.Can this be done?What other info do you need? Link to comment Share on other sites More sharing options...
Members mrbrown49 Posted June 4, 2008 Members Share Posted June 4, 2008 It could work with enough time and money. Early amps were pretty much adapted radio circuits. Do you know enough about electronics to make this happen though. What kind of tubes are in that radio, and are they still available? Link to comment Share on other sites More sharing options...
Members daklander Posted June 5, 2008 Author Members Share Posted June 5, 2008 I'll pull the tubes and look, or the types may be listed on the diagram. Un-fortunately I there is no schematic I can find within the housing. Electronics, it's been a long time with this kind of stuff but years ago did attend school for radio/television. Link to comment Share on other sites More sharing options...
Members GomezAddams1 Posted June 5, 2008 Members Share Posted June 5, 2008 No! do not pursue this!!!! There is a huge safety issue and a technical issue. If the radio has no transformer, that means it has no isolation from the power line. That means that the "ground" of the radio is connected *directly* to one side of the power line. Your guitar will be connected to this same ground. Now, in theory, a grounded plug (or even a polarized plug - one with one blade wider than the other) would mean that your guitar would be connected to the "cold" side of the power line. However, if the circuit you are plugged into is wired incorrrectly, your guitar will be connected to the "hot" side of the line and when you touch it with one hand, and anything thing else that is grounded with the other hand, you've just made a nice conductive path from 120V to ground. Worse yet - the current path goes straight through your heart. Is every outlet you'll ever plug into wired correctly? Want to bet your life on it? The reason they could get away with this in old radios and TVs was that all of the circuitry was enclosed in plastic or wood with no conductive (metallic) path to the user. The technical issue you'd run into is that the heaters of the tubes are wired in series so that the total voltage required is 120V. You'd have to keep all the tubes (and add none). Link to comment Share on other sites More sharing options...
Members daklander Posted June 5, 2008 Author Members Share Posted June 5, 2008 No! do not pursue this!!!!There is a huge safety issue and a technical issue.......... OK, that's kind of what I thought 'cause it seems somewhere along the line I've heard that before, & that's why I'm asking.So you're saying with this layout there would be no way to add a ground to the circuit?If that's the case, of course I'll toss that idea into the trash can. Link to comment Share on other sites More sharing options...
Members dcindc Posted June 11, 2008 Members Share Posted June 11, 2008 Yeah basically what Opus said. Probably a version fo the All American Five radio circuit. You can rape all the parts out of it though. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted June 11, 2008 Members Share Posted June 11, 2008 I used to mess with old AM radios when I was a kid. The output transforners that stepped the 70 volts or so down to handel an 8 ohm speaker were usually mounted on the speaker itself. You need to disconnect the radio signal coming into the preamp tube. You can tap an input to the amp from the same point or the volume control itself. Problem is the amp circuits are so pitifully weak they wont drive a guitar without preamp mods/additions, Also you still have all the RF circuitry running which is a waste. To get around the grounding issue you can use an old trick used make a guitar safe from grounding. You put a hi uf cap between the frame and the inputs ground. You may get a tingle with a bad ground but not enough amps to kill. If youre into modding though you'd be better off finding an old tube hi fi or bogen like tube amp to modify. They need different caps to be revoiced for guitar but you'll be left with a few more watts to drive a speaker decently. Link to comment Share on other sites More sharing options...
Members daklander Posted June 12, 2008 Author Members Share Posted June 12, 2008 'K, thanks guys. I'm convinced. I'll put it on ebay as a collectable. Link to comment Share on other sites More sharing options...
Members tedmich Posted June 14, 2008 Members Share Posted June 14, 2008 FYI these crazy dudes do a lot to mod old amps (from organs etc) into gitar amps, WEB site is a train wreck, takes diggin.. http://www.vacuumtubecollective.com/ check their Trinity 18 based schematic! http://www.vacuumtubecollective.com/schematics/Bradshaw18TMBPowerscale.jpg Link to comment Share on other sites More sharing options...
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