TrueTone D1143 Radio to Amp

fuzzsniffvoyage

Well-known member
I acquired this old radio made in 1941 or 42. It's a tube radio and I'm wanting to convert it to a guitar amp. Since it has 2-6K6 tubes, which are very close to a 6V6, and the rectifier tube is a 5Y3, it seems very plausible for a Fender Champ style amp.
I can't seem to locate a preamp section in the schematics for the radio. I do not want to purchase another power transformer to power a 12ax7 circuit. I already have the 12ax7 tube and tube socket.
Also the speaker seems to be powered. So instead of the preamp, could I use the speaker?
Any help or ideas would be much appreciated.
As for the power cord, I have a borked computer monitor that I'm planning on repurposing the AC cord an the power jack and putting a fuse in there too.
View attachment truetoned1143.pdf20180920_093207.jpg20180919_153215.jpg20180919_153111.jpg
 
Hey,
The speaker isn't 'powered' as such. It requires power.
Actually, a lot like a capacitor microphone does.

Instead of having a permanent magnet, those old boys used an electro-magnet instead.

I don't know much about them but removal/replacement may not be as simple as removing power and hooking up a regular modern speaker.
I know you didn't suggest that; Just throwing it out there.

I don't think you should need any external or additional preamp.
Just find the right point between tuner and amplifier and tap in there. Depending how it's setup, there may be a volume or tone control at that point?

Anyway, I'll get out of the road and let someone who knows tell you more. :P

Any pics of the guts?
 

fuzzsniffvoyage

Well-known member
I'd like to at least delete the radio circuits maybe cut down on some noise.

And I did not even try to plug it in, the condition of the power cord is dangerous looking. So that'll be my 1st order of business. There's also some broken cord in a couple places. 1 is one of the yellow cables to the speaker coming off of one of the 6K6 tubes.


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fuzzsniffvoyage

Well-known member
Hey,
The speaker isn't 'powered' as such. It requires power.
Actually, a lot like a capacitor microphone does.

Instead of having a permanent magnet, those old boys used an electro-magnet instead.

I don't know much about them but removal/replacement may not be as simple as removing power and hooking up a regular modern speaker.
I know you didn't suggest that; Just throwing it out there.

I don't think you should need any external or additional preamp.
Just find the right point between tuner and amplifier and tap in there. Depending how it's setup, there may be a volume or tone control at that point?

Anyway, I'll get out of the road and let someone who knows tell you more. :P

Any pics of the guts?

Pic's posted.

If I can I'll use the old speaker, looks in decent condition, but I'll have to do some testing. Maybe it'll sound spectacular.
 

fuzzsniffvoyage

Well-known member
I'm no expert, but I think it may act as part of the power supply. Using a permanent magnet speaker might mean reconfiguring the power supply.

I don't want to do that. I'm trying to do this on the cheap but still sound decent or unique.

The worst I can do is blow the thing up. (I'll keep fingers and toes out of the circuit)
 
Oh, I missed the pdf in the first post.

The phono jack is something of a hint.... :P
With the input switch in that position, the radio section would effectively disconnected from the circuit.
 

arcaxis

Well-known member
The 6SA7 and 6SK7 can be removed. Those are for the RF and IF stages.
The 6SQ7 can stay if you use its triode as your first stage in the amp, but it isn't going to give as much gain as two stages of your 12AX7 which can be wired for 6.3vac.
The 6J5 is the phase inverter for the push/pull 6K6's and the 5Y3 is the rectifier.
The 6U5, if you got it with the radio is a 'magic eye' tube used for tuning stations in. It would be neat to use it for audio signal indication, but it's in the detection circuit.

If the speaker doesn't work out you might look at putting a resistor in place of the coil in the power supply circuit. An actual iron choke would likely filter better, but a resistor may suffice. I've done this years ago with a similar vintage radio fix. Winding resistance shows 900 ohms. A 1000 ohm wirewound resistor of a hefty wattage would be worth a try. The old multi-section electrolytic can could be replaced with a couple higher value (20-25uf) caps which may help DC filtering. Note the voltage rating on the schematic when replacing.

The attached PDF might help a bit :D
Nostalgia Air: Western Auto Supply Co. - D1143, Issue A
 

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arcaxis

Well-known member
- Some 'chop' points marked in red and pull the tubes I mentioned in the previous post.
- Change the 'phono' jack to a 1/4" jack and put switch to 'phono'. Try it with some pedals that have some gain.
- The 'optional cut' is if the tone circuit it goes to takes out high end of the guitar. Maybe try it with and then unsolder the 68000 ohm resistor off the pot to see if it changes anything.
 

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If it works out anything like the transistor radio guitar amp mods, it'll thank you for putting a treble booster in front of it.
Looking forward to hearing how you get on. :)
 

arcaxis

Well-known member
Rather than put a wirewound resistor in in place of the speaker coil, maybe a mod to the circuit I have circled in red. Still use about a 1000 ohms resistor, but maybe a 1 or 2 watt jobby.....
 

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fuzzsniffvoyage

Well-known member
As to fuses, what amp should I use? I was thinking a 2amp would do.

And I have 3 fuse holders that I could use. Which one?

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I'm sure they have proper names, have no idea what they are. Any help?

Thanks!
 
Hey man,
I didn't see your last posts until now. Not sure why.

What was the outcome with this? Did you get up and running?
 

ecc83

Well-known member
I too found this thread late but Mark seems to have done a bang up job!

Cut my apprentice teeth on similar radios, not many American models, the odd Philco but I always hated their weird schematic layout and found them hard to follow! The attachment is also low resolution. Is that a "concertina" phase inverter? If so the amp will have very little gain.

The most "elegant" way to sort a radio like that is to strip out all the RF components save the valve bases and tagstrips. Then the bases can be used either for an octal double triode like the 6SN7GT or use an octal base to make a B9A adaptor (the ECC83 only needs 8 pins) Or, strap an RF pentode as a triode, or two.

The energized speaker is indeed a filter choke but the rectifier current causes hum and so there is usually a humbucking circuit in the secondary path. The speakers usually had a Paxolin "spider" and thus a high cone resonance, doubt it will sound good.

Fusing? 2AT for mains input and 100mA T for the HT...DO fit an HT fuse!! Since there is an IEC mains con'' best to stay modern and use 20mm fuses.

I have to say, OP did not read as terribly experienced with electricity? I do hope the lack of further information is not a sign of some terrible happening?

Dave.
 
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