Help! Transistor radio converted into amp

[Soulwyvern84]

Hi, I'm new here... I have a few questions related to converting an old transistor radio into a guitar amplifier. I've looked at several videos and posts about it, but they all seem very vague on exactly how to do it. What I'm confused about is what is used to touch the volume potentiometer, and also, does that somehow make the radio aspect of the radio stop functioning, or...? I saw that you have to find the diode and disconnect it, but I'm not very good at electronics yet... I'm not understanding... how do you solder the input jack to the volume, what type of audio input jack is required and how to drill the appropriate size hole for the input jack or output jack...

 

[73's de Edd]

Sir Soulwyvern84 . . . . . . .


I'm thinking that feat might be comparative to my using a sled dog on a "hamster wheel" to power my big Mer-say-dees . . . .MUSH !

First of all the "radio" needs to be up in the power order of a "Boom Box" to get any appreciable playing level.
You might then think that the connection of the guitar to the radio would be the installation of a female phone jack for the guitars male phone plug.
With need of only 2 connections made to its mate in the radio.
The connections would be across the two very extreme ends of the volume control.
That then gets the guitar wired into the "radio".
Now here is where the "dog" analogy comes in, your volume control is requiring in the order of a half of a volt of audio signal across it.
Your guitar pick up is putting out in the order of a mere five thousandths of a volt ..
Sooooo you need to amplify that guitar pick ups signal in excess of 100 times.
So you need a preamp installed inline between the two.
References to usable possibilities:

https://www.google.com/search?newwi...18.0....0...1c.1.64.hp..0.18.1707.Djruj3e8a1o

OR use a separate wireless mike to acoustically pick up the sound and it transmits a radio signal to your boom box's radio.

OR use a professional musicians unit in which the guitar pick up plugs into it and that unit sends a FM signal to the boom boxes radio receiver.


73's de Edd

.

 

[Soulwyvern84]

I'm a Ma'am not a sir, lol... Maybe I should go out and get a dunce hat, I'm not understanding what you are saying exactly. I know the volume is not loud on these little radios, but I like the gnarly lo fidelity sound of them. I just wanted some clarification to my questions because this is my second attempt at messing around with electronics. I don't want to mess up. I know in one of the videos the guy cuts the ac power so you don't get electrocuted. These are really for cigar box guitars, but I saw a different video of one with a regular electric guitar, it didn't sound bad at all. I need a basic step by step here. I found 3 transistor radios, one to practice on, one for myself, and one for my girlfriend. I'd really like to start the project soon.

 

[Soulwyvern84]

And thank you for answering a newbie

 

[Soulwyvern84]

Also this is the video I'm mainly referring to...

 

[73's de Edd]

.Mme . .Soulwyvern84


Ahhhh yes . . . .Sir . . . OR . . . Madam . . .and we so infrequently, are visited by the fairer sex at this site.
The only variant on your video was his going back one stage before the volume control to acquire a little of that required gain I had mentioned earlier.
Instruction could be supplied from here, if merely seeing some closeups of the volume control area via clear close up photos

73's de Edd

 

[Bluejets]

Maybe like this....and please use a battery radio...keep away from mains type.

 

[Soulwyvern84]

Thank you all! I'm going to go ahead and disable the ac power and tinker a bit.

 

[Bluejets]

Thank you all! I'm going to go ahead and disable the ac power and tinker a bit.

My reference to using a battery type radio was to keep you well away from any mains supply, whether it is working on the device or not.
There is a possibility you could inadvertantly connect into the wrong part and do yourself or others an injury.

 

[Soulwyvern84]

ok, thank you for the advice... also found more advice on it from the man who was showing how to do it in the video on cigar box nation for anyone else interested
Comment by smojo on December 18, 2013 at 3:25am

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.
Comment by smojo on February 25, 2013 at 3:29am


Volume pot is the place. There's three lugs on it. One will go to ground so the ground on your jack socket needs to be wired to that. The "hot" or tip of your jack socket goes to one of the others, usually the centre. Connect to it then try a guitar plugged in and see if the volume pot still works properly. If the sound level doesn't change then move the wire to the other end lug and try again. You usually need to chop the feed that goes to that to stop the radio signal coming through.

 

[Soulwyvern84]

I am worried I will hurt myself, but I don't want to be deterred from trying anything. So How would I install a preamp?

 

[Soulwyvern84]

And at bluejets, are you saying that if I cut the ac power cord that it still functions... I think I may need to get a book first, do you agree? So should I get a book on basic electronics or how to repair old radios and amplifiers to get a better idea of whats going on inside these things? Or is there something you all could advise without spoiling the fun of discovery?

 

[Soulwyvern84]

I just don't want to discover that I'm electrocuted, lol

 

[Bluejets]

And at bluejets, are you saying that if I cut the ac power cord that it still functions... I think I may need to get a book first, do you agree? So should I get a book on basic electronics or how to repair old radios and amplifiers to get a better idea of whats going on inside these things? Or is there something you all could advise without spoiling the fun of discovery?

In a mains connected device, when you disconnect the power there still may remain some charge in the power supply capacitors that can give you quite a nasty belt.
However, the point about using a battery powered radio was that there may be some smoke if you do any modifications incorrectly.
But with mains connected devices there is a possibility of a fatality if you get things wrong when you plug it back into the power .

 

[73's de Edd]

.


Soulwyvern84 . . . . .so that makes you 32 ?

Give us the brand and model number of your radio, so that we will then know what you are working with, and only then, maybe we can mark an X for you and thereby tell you where to dig .

.73's de Edd

 

[BobK]

In a mains connected device, when you disconnect the power there still may remain some charge in the power supply capacitors that can give you quite a nasty belt.
However, the point about using a battery powered radio was that there may be some smoke if you do any modifications incorrectly.
But with mains connected devices there is a possibility of a fatality if you get things wrong when you plug it back into the power .

Not likely in a mains powered transistor radio. The mains are most likely only connected to the primary of a transformer and after that it is all low voltage.

Just don't tinker with it when it is plugged in.

Bob

 

[Bluejets]

It may be low voltage but the caps can store a charge enough to give one a surprising wack.

 

[73's de Edd]

.


Sires . . . .

Vel it looks like ve vill be awaitinks to see vat radio dot she is havink . . . . .

I'm expecting its 6 or 9 VDC supply, stored in its 220 ufd filter cap(s) to only be "whacking" my errant screwdriver or test probe tip.

73's de Edd

.

 

[BobK]

It may be low voltage but the caps can store a charge enough to give one a surprising wack.

Really? try touching the terminals of a 12V car battery. They can supply 400A. Why no whack? Or, if you prefer, charge up a 10000uF cap from the car battery and see if that will give you a whack.

As long as there are no capacitors charged to more than about 30V there is not danger of shock, unless you puncture the skin or use your tongue as a probe.

Bob

 

[Soulwyvern84]

I have about 5 different ones I want to convert, two of which I want to work on soon. I just got one in the mail yesterday and it is a zenith royal, hold on let me check the numbers...