Converting an Old Radio to My First DIY Amp with a Celestion, Suggestions?

[Scruffie]

Right... i've just harvested some old 60's radios from my Grandads old garage for parts and while going through I decided one of the old Radio cases would make a great enclosure (and recycle) for my first DIY amp.

So I went through and pulled out all the old lovely germaniums for other projects (although if germaniums are good for amps or preamps or whatever, they can go in) etc. so i've got the case spare which should look great with a polish as it's mostly brass & wood but I also noticed three of the Radios had small Celestion speakers in perfect condition, I don't know much about speakers (or building amps really) but that was a name I recognised from the Vox amps.

I've got a choice of 3 Ohm Ratings a 70 Ohm, 25 Ohm & 30 Ohm Speaker, I realise usually amps use 8,16 & 32 but I figured I could get the right rating by running a resistor in parallel with one correct? or that perhaps some SS amps don't care what Ohm rating they see that much.

Just because they have a brand name on them doesn't make the speakers all that good though i'm sure so is there anything I should look for and do certain Ohm speakers sound different if not i'l just do a shoot out when it comes to it.

Next is the question, what amp to put inside, the case isn't huge but it could fit 2 tubes inside and easily fit a sub-mini amp but for now i've gone with the idea of doing something solid state so I need to choose what goes in and what are the best options, being the age & appearence it is, i'm thinking of something with a voxish/fender voiceing but for a small amp I realise that's probably not very feasible.

I also got some very small Transformers (Octavia size but not measured) from inside the radios but if they powered the speaker in the first place I guess they'll be okay for a small amp but I could also go the route (which would probably be alot easier) of something like the Noisy Cricket, Little Gem or Ruby so are there any suggestions of what I should build in?

Finally, I obviously have the original components from inside the radios, I know that using the old Carbon comp resistors other than for Mojo wont have any affect unless I build a tube amp inside but I got a load of Hunts Brand Capacitors, are these a decent brand or were they the Mylars of the day? I know caps are very subjective but i'm recycling it all and just wondered if I should use them for other things or they were really valuable so I should save them for something special or... well what.

Sorry if that was all a bit vague but if anyone has any suggestions I think this could be a good project and I can put pictures up of anything if it'll help anyone with ideas or identifying etc.

Thanks in Advance though!

[PRR]

If these are 5-tube AC/DC radios, DON'T use them for guitar amps as-is; potential death-trap.

I am going to assume that these transistor radios have power transformers.

> I went through and pulled out all the old lovely germaniums

Why? A radio HAS an audio amplifier. This amplifier is usually a good match to the original speaker; power, tone, -impedance-. You DON'T want to start by gutting it!

Find the Volume control. One end is grounded. Connect gitar jack shell there. Disconnect the wire at the other end of the volume pot. Connect guitar jack tip there.

This simple "mod" WILL play. On some radios very well, others might make you work hard, and a 1-transistor booster in front will make it play easier.

> small Celestion speakers

Celestion made EVERY kind of speaker, from $999 la-di-dah Hi-Fidelity to the half-buck junk in low-low-price radios.

It may be interesting, because sometimes the "cheap" speakers came out unexpectedly nice.

It would also be nice to know what the speaker power rating was. Or what the original radio AMP rating was, because they never put too much amp for the speaker (or too much speaker for the amp), because that was bad for profit.

You can run any impedance, just design the amp for it. "25" will be fine on a 16 or 32 tap. "70" will work on a 32 tap. It won't suck the amplifier's maximum power, but these are cheap low-power speakers so it is not about "maximum power". If you get sweet small sound, be happy.

The odd impedances ARE odd because few-ohm speakers are cheapest. (Did I mention that radio designers are cheap?) The higher impedances use thinner wire which is more work to draw and wind, breaks a lot. Otherwise, any impedance can sound the same. The fact they used odd impedances says that these are not transformer-output radios.

If you can't restore the amps you scavanged, and want a quickie to hear the speakers, use an LM386 at 12V. This will put 0.6W-0.2W into these impedances, probably "safe", and plenty loud. If you don't go "ugh" (some radio speakers WERE "ugh"), you could tubify with a small IF or video pentode; 6AU6 is common and good. The problem is finding an OT to couple ~~10K to 25-70 ohms, and small enough to put some iron-sound into a third-Watt signal.

[Scruffie]

No no, I forgot to mention they were Transistor radios, no deadly tubes.

The radios needed gutting because of several factors a) I wanted germaniums for other projects, b)Several of them had, had batteries leak inside them so were a mess and didn't work properly, c) Some of them there was no access without gutting and d) I'd prefer to start with a fresh project anyway but that's not really important, they were going to the skip anyway.

I'l guess these are the half a buck junk Celestions (not that there's not potential for them to sound good as you say) there's no model names as such or distinctive markings, they're just Celestion so that'll be a job to try and see what sounds best although one of them looks remarkably higher quality than the other two so i'l probably start with that.

Original ratings... I haven't come across any indications but i'l have a look in the morning for that.

(Did I mention that radio designers are cheap?)

You did, I have no idea what these radios were like back in the day when they worked properly though, obviously a commercial product would be cheaply made as it's at no benefit for the company to spend more for a cheap product but for all I know these were of a slighter better quality makes, there were some obviously cheap bakelite radios and then these brass and wood which look like they were nicer and where the Celestions came from, the bakelite radios just had unbranded speakers.

I had no intention of restoring the amps from the off, although if I wanted to it still is a possibility, I wanted the insides and thought, why waste the rest if it can be put to some use, if I was going to put something tube inside it'd probably be along the lines of one of Frequency Centrals designs or the Firefly amp, nothing fancy and with only one transformer, a 386 amp may be all I need though, i'm gunna hazzard a guess that the speakers are rated for 2-3W though.

[petemoore]

  Radio/Phono, other types of conversion to guitar amps:
 First thing to check is if it has a PT, if so, find a schematic or see if the 'third prong' and grounded chassis is an option, it isn't always an option.
 Outside, standing back...plug it in and see what it does.
 Then consider if the cap and tube/tube socket replacements or complete new circuit injection are worth the options consideration.
 The little old speaker sound can be really sweet. Size of the voice coil can give hint as to power handling, as can what tube was driving it, even slight cone-cry hints may soon be too late for old voice coil glue, savor and take it easy on it.
 Old resistors are nice, as are new filter caps.
  Some relatively inexpensive 'decent platform' tube amplifiers can be had, readymade.    
 

[Scruffie]

 Radio/Phono, other types of conversion to guitar amps:
 First thing to check is if it has a PT, if so, find a schematic or see if the 'third prong' and grounded chassis is an option, it isn't always an option.
 Outside, standing back...plug it in and see what it does.
 Then consider if the cap and tube/tube socket replacements or complete new circuit injection are worth the options consideration.
 The little old speaker sound can be really sweet. Size of the voice coil can give hint as to power handling, as can what tube was driving it, even slight cone-cry hints may soon be too late for old voice coil glue, savor and take it easy on it.
 Old resistors are nice, as are new filter caps.
 Some relatively inexpensive 'decent platform' tube amplifiers can be had, readymade.    

Doesn't look like there is any chance of finding the schematics for these radios without paying and several of them are missing model numbers making tracking down the correct one difficult.
There's no tubes to replace, it's just an empty wooden case at present with some speakers and a few radios worth of components waiting for a suitable project to go inside of it, although I could pick up a tube radio cheaply, is there any particular kind I should look for with this? but that would be another project altogether.
There's no damage to the cones, they're in almost new condition apart from a bit of built up dust but I will take it easy on them as they're only small speakers, two of them are  4" cones and the smaller is 3 1/2"
Here's some pictures of the speakers & their cones if they're of any use:

[petemoore]

  Sometimes a little lightweight cone/speaker like that is just the right fit.
  The best thing for 'kitchen table' jamms.
  Half a watt or so gets it going, that's about all it takes.
  If you can use the cabinet, an LM386 amp is a pretty quick wire-up.

[Scruffie]

 Sometimes a little lightweight cone/speaker like that is just the right fit.
 The best thing for 'kitchen table' jamms.
 Half a watt or so gets it going, that's about all it takes.
 If you can use the cabinet, an LM386 amp is a pretty quick wire-up.

Yup, that's exactly what I want from this, something for kitchen table jams but with a little trick up its sleeve tonewise.
I can indeed use the cabinet, its perfect for the job which is where the whole idea to turn it into an Amp came from.



Guess i'll stick a 386 on the breadboard and see what takes my fancy.

[Eb7+9]

The best thing for 'kitchen table' jamms.

this thing is begging to be turned into a Theremin/Amp with effect loop ... you just never know when Page might show up to your kitchen jam

[markeebee]

Hunts caps are notoriously shoddy, they have a rep for being very unreliable.  As the ones you have are old anyway, and there's no way of knowing what usage and abusage they've had, I think it would be sensible to ditch them.

You can't go wrong with a Ruby.  You could add a Professor Tweed/English Channel for more Fender or Voxy goodness.

Or, even more fun, the Sopht Ruby Tuby.

[Scruffie]

Hunts caps are notoriously shoddy, they have a rep for being very unreliable.  As the ones you have are old anyway, and there's no way of knowing what usage and abusage they've had, I think it would be sensible to ditch them.

You can't go wrong with a Ruby.  You could add a Professor Tweed/English Channel for more Fender or Voxy goodness.

Or, even more fun, the Sopht Ruby Tuby.

Oh really? That's a shame they looked like quite nice caps and they had longer leads than the Phillips Mustard caps I salvaged but i'l use those instead perhaps, or save them for later down the line.

Yeah i've wanted to do an English channel for a while so perhaps now's the time to stick one in but I haven't heard of the Sopht Ruby Tuby, i'l have to have a look into that one.

The best thing for 'kitchen table' jamms.

this thing is begging to be turned into a Theremin/Amp with effect loop ... you just never know when Page might show up to your kitchen jam

Nah, Page has got his own theremin in the Kitchen already, always playing it, he doesn't need another one and to be honest, it'll just be another thing to keep him in there, very difficult to get rid of these old rock stars once they've made a home in your kitchen.

[markeebee]

Ha!  I thought that banging noise in the middle of the night was just dodgy plumbing. Turns out to be Ginger Baker behind the fridge.

Sopht Ruby Tuby:  http://www.sophtamps.ca/mambo/index.php?option=com_content&task=view&id=28&Itemid=39

[Scruffie]

And there we all were thinking Ginger had been kicked outta England and he was behind your fridge the whole time! You'll have to shoe him out with a broom handle.

Very nice markeebee, thanks for the link, any idea how the Ruby Tuby sound clips compare to just a straight out ruby? Am I going to get alot out of the tubes at only 12V or would it be more wise to stick with a FET tube arrangement like the Fetzer infront of the Ruby? I was considering using one of the Germaniums out the amp to have a built in rangemaster to drive the 386 amp aswell...

[markeebee]

I dunno that the RT will necessarily sound a whole lot better than a 'normal' Ruby.  On the other hand, and I don't know if it's all in the mind, but I think that an amp with a valve front end (even if it's low voltage) seems to react better to pedals than a solid state amp.  So +1 for the rangemaster idea.

You can get a 12AX7 for a fiver on ebay, what's the worst that can happen?   

Oh, it's also worth looking at ECH83 valves.  I got a couple for about 3 quid each.  They're designed to run on 12V quite happily, and will have a bit more clean headroom than the 12AX7 in the RT.  I was thinking of making something like this, but with a LM386 output instead of the TDA:

http://www.coldcity.com/index.php/hybrid-guitar-amp/



I managed to tempt Ginger out with a saucer of vodka, but the cat chased him under the cooker, and now he's having a bit of a face off there with the Rubettes.  Could be a long night....   

[Scruffie]

Wouldn't want to be in your kitchen this evening! sounds like you've almost got an impromptu jam going on, atleast Page just sits in his corner and makes strange noises on his theremin quietly... this is turning into something remarkably simmilar to an unwritten python sketch.

Well then I think a Rangemaster + Ruby it is untill I can afford to get hold of some tubes (I can't even afford the fiver at the moment  ) but you can't complain at a fiver each, 'bout time I started playing with tubes anyway.

Okay, think i'l go for the ECH83 then, I suppose that's a bit like how the Valvecaster runs a bit better off the 12AU7 than it does the AX7 Then again I know nothing of tubes but I also thought I remembered seeing some designed to work off 9V like a 9AX7, but that could've been a dream.

Thanks for the links and suggestions 

[PRR]

> I also thought I remembered seeing some designed to work off 9V like a 9AX7

There's "two parts" of a tube.

The part the audio goes through needs 50V-500V to pass decent power. The car-radio tube "did" run the signal on 6V-12V, very-very-faint. The loudspeaker stage was a transistor (or now a chip).

To make it work at all, it needs a "heater". That can be any voltage, lower is a little cheaper. Often 6V, 12V, 2V, but also off values like 9V.

Think of an electric car (if we ever have them again). The headlights will still be standard 12V units: available, rugged. The motor "has" to be a higher voltages to get decent power without incredibly fat cables: 100V to 500V are used.

Don't get power-mad. Table-radios were generally 1 Watt; battery radios much less. And they were not expected to play FULL power ALL night long. So you should be looking at part-Watt designs, not few-Watt designs.

[Scruffie]

> I also thought I remembered seeing some designed to work off 9V like a 9AX7

There's "two parts" of a tube.

The part the audio goes through needs 50V-500V to pass decent power. The car-radio tube "did" run the signal on 6V-12V, very-very-faint. The loudspeaker stage was a transistor (or now a chip).

To make it work at all, it needs a "heater". That can be any voltage, lower is a little cheaper. Often 6V, 12V, 2V, but also off values like 9V.

Think of an electric car (if we ever have them again). The headlights will still be standard 12V units: available, rugged. The motor "has" to be a higher voltages to get decent power without incredibly fat cables: 100V to 500V are used.

Don't get power-mad. Table-radios were generally 1 Watt; battery radios much less. And they were not expected to play FULL power ALL night long. So you should be looking at part-Watt designs, not few-Watt designs.

Oh no, i'm not interested in extra power exactly, just ways to get a better tone and reasonable clean volume, which I know is asking alot for a small table top amp but why not try! Cause you'll fail is probably the correct answer to that.

If it's the case that adding a tube/s is a bit excessive though, although for a hybrid amp i'd assume it was okay, i'l just drop them and go back to the idea of having a dallas rangemaster run into it, it may end up that way anyway, after cleaning the case up this evening and installing the speaker there's not alot of room without cramping stuff and i'd rather have an easily serviceable mini amp... on the plus side it's looking really good with a clean & some brasso, i've just gotta decide the best place to put the controls on it now...

[markeebee]

Does this work?