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Discussion Starter #1
I have been meaning to pull the amp out of this old radio for a very long time! There are a couple tubes, some wiring and caps, a transformer of some sort? It’s GE radio (I think from the 40’s) and it had a phonograph under the lid. I’m planning make the cabinet into a jukebox type stereo using a car CD player. I don’t think the tube amp would be suitable for a guitar, but correct me if I’m wrong. There’s a bunch of cloth covered and braided wiring that I’d like to repurpose for some future project (maybe rewiring a guitar?). I really am not very knowledgeable about electronics otherwise, so I’m hoping that someone here will let me know if there is something else here that might be interesting.


Old caps, tubes are a Marconi 5Y4G & Sylvania 6L6. Not sure if either are good.
 

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Discussion Starter #3
So, here’s what I determined:
It’s a model KL-5 radio-phonograph from 1941/1942
It has a phone input and AC power outlet (maybe for an accessory?)
It has 2 tubes, and the 6L6 output is also used for guitar amps, I have a single stage Crate tube amp with an el34 and I might try testing the 6l6 in it.
The other tube is the rectifier tube and I don’t see it associated with guitar on google.
Lastly, the schematic identifies the transformer as a T1 which might just mean #1 transformer. I don’t know if it is suitable for a guitar application.
 

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Is the output transformer on the speaker? The 6L6 probably should not be in there. The 6F6's modern day tube would be the 6V6 which would match the output transformer better. The high value parts would be the transformers, the 6L6 if you can use it in another amp. The 5Y4 rectifier tube and the the 6SQ7 are useable. You can make a Champ style amp, a 6V6 single ended amp. If you are inclined to make a head out of it you can reuse the chassis and leave the heater wires in place as well as the high voltage wiring going to the sockets. The bad news, the speaker had a field coil in place of a regular magnet and the coil is used in the power supply and the voltage will be higher than what the radio was designed for. The good news, Fender and others ran higher voltages on their amps as compared to data sheet recommendations. Also the voltage can be knocked down with a resistor reducing hum.

So usable stuff but might take some help putting a circuit in place. With what you have adding another 6SQ7 can give you a champ, Tweed or Blackface with bass and treble. With a two triode tube like the 6SL7 or 6SC7 you can have a 5E3 front end. Now you got me interested in trying a 5E3 into a single ended output tube.
 

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Discussion Starter #5
Is the output transformer on the speaker?
Thank-you for the reply! I’m not sure what you mean by this /\ I am assuming the transformer is the big black box at the edge of the chassis in my photo. I’ve unplugged the speaker - it’s still in the cabinet.
But I was surprised by the 6l6 too, I think that someone’s been into this amp already though. The orange and yellow capacitors don’t look like they are from 1941 either.
I do have a spare (guitar speaker) cab here, so this might form some sort of project in itself if I muster up the courage. I would probably disassemble what’s there and then use the chassis and whatever other parts are good still.
 

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The schematic shows t1, t2, and the speaker/coil. T1 is the power transformer T2 on the schematic is the output transformer which was likely mounted to the speaker on the speaker basket/frame as @Printer2 mentioned. The field coil/speaker was mentioned as well. The speaker in the original cabinet doesn't use a permanent magnet. It is a field coil/electrodynamic speaker which has a coil that if im not mistaken is used in the circuit similar to a power supply choke. If you have the original cabinet and speaker you can use it for your project or you can potentially salvage the coil to use in the power supply to keep the voltages in line with the schematic.
 

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I modified an old radio by disconnecting the wire going to the am receiver and running it to a 1/4” jack.

It took about 20 mins.
It sounds pretty awesome in a low fi link wray kind of way.

Try that before going too far with it.
you will know if it sounds okay with spending a lot of time or money on it.

Nathan
 

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Discussion Starter #8
The schematic shows t1, t2, and the speaker/coil. T1 is the power transformer T2 on the schematic is the output transformer which was likely mounted to the speaker on the speaker basket/frame as @Printer2 mentioned. The field coil/speaker was mentioned as well. The speaker in the original cabinet doesn't use a permanent magnet. It is a field coil/electrodynamic speaker which has a coil that if im not mistaken is used in the circuit similar to a power supply choke. If you have the original cabinet and speaker you can use it for your project or you can potentially salvage the coil to use in the power supply to keep the voltages in line with the schematic.
Ah ha! I’ll pull the speaker next, I haven’t even looked at it yet but assume it’s complete with whatever components belong with it.
 

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Discussion Starter #9
I modified an old radio by disconnecting the wire going to the am receiver and running it to a 1/4” jack.

It took about 20 mins.
It sounds pretty awesome in a low fi link wray kind of way.

Try that before going too far with it.
you will know if it sounds okay with spending a lot of time or money on it.

Nathan
Good idea in principle but I’m not sure it’s safe to plug in as it sits. I don’t plan on putting much cash into though, I’ve got lots of amps anyway. This amp is just an afterthought following my ‘jukebox’ project.
 

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it's hard to tell if thats the OT or the field coil. I think its the ot because it appears to be attached to the speaker plug. However, I can't see under the speaker bell to see whats under there. if theres an inductor/coil with a connection to the b+ line which would be the field coil
 

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The plug has three pins. The primary of the transformer has two ends. The field coil/choke has two ends. The primary and the choke are connected to each other.
 

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The plug has three pins. The primary of the transformer has two ends. The field coil/choke has two ends. The primary and the choke are connected to each other.
Yes. Also, the field coil creates an electromagnet for the speaker, so it will always be where the speaker magnet is located.
 

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Before you go too far, it's fair to say all the coupling caps, resistors and electrlytic/oil caps would have to be changed out. I can see someone started to refurb but there is much there that still needs replacing.There is no good reason to power up something like this with any original components in it. As a matter of fact it might be dangerous. The radio is over 70 years old.
 

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Discussion Starter #16
Thanks, I have no intention of plugging it in. It’s all dissasembled and boxed up. The tubes are on my dresser and I’m using the cabinet to house a car CD head unit which will be a ‘home brew’ retro chique stereo. I may use the chassis as a starting point for a diy amp build sometime in the future if I muster up the enthusiasm.
 
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