I recently received an old tube radio (Philco 90) from a friend, and I am playing with ideas of what to do with it. I would like to use the parts to build a small 5-10W amp but im not sure where to start.
I was planning on looking up schematics for the tubes (there are 9 but I think they are fairly specific to Philco radios) and designing a circuit around 2 or 3 of them. If I need to get some new transformers I will. The main issue is, the tubes are hard to come by so once they go, thats pretty much it.
Thoughts? Suggestions?
Old Tube Radio Amp
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Jack Hester
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Re: Old Tube Radio Amp
You'll find any and all of your tubes on eBay, if you need replacements. Wouldn't be a bad idea to get extras for the ones that you use.
Typically, old radios did not use a power transformer. Just rectified the incoming line voltage. To be safe, you will want to get an isolation transformer. What are the tube numbers? A lot, if not most, of those tubes have 25 and 35 volt filaments.
I would suggest that you find a schematic for your radio, and trace the actual circuit, so that you can see how it's put together. More than likely, the power supply will need new capacitors. You'll know when you power it up the first time, by the hum that doesn't change when you move the volume.
If you've not built an amp before, it can be an interesting project. You can modify or eliminate everything before the power amp, and build a pre-amp for your instrument.
Also, build yourself a lamp limiter for powering up your builds, for the first time. Or in this case, powering up an old radio for the first time. Sometimes, you can re-form the old capacitors, and continue to use them.
Jack
Typically, old radios did not use a power transformer. Just rectified the incoming line voltage. To be safe, you will want to get an isolation transformer. What are the tube numbers? A lot, if not most, of those tubes have 25 and 35 volt filaments.
I would suggest that you find a schematic for your radio, and trace the actual circuit, so that you can see how it's put together. More than likely, the power supply will need new capacitors. You'll know when you power it up the first time, by the hum that doesn't change when you move the volume.
If you've not built an amp before, it can be an interesting project. You can modify or eliminate everything before the power amp, and build a pre-amp for your instrument.
Also, build yourself a lamp limiter for powering up your builds, for the first time. Or in this case, powering up an old radio for the first time. Sometimes, you can re-form the old capacitors, and continue to use them.
Jack
Re: Old Tube Radio Amp
I would just restore it or leave it as is.jayfroo wrote:I recently received an old tube radio (Philco 90) from a friend, and I am playing with ideas of what to do with it.
Usually not such a good idea. You can merely recycle the power supply and the AF amp parts, which in these kinds of radios makes about 10% of all the stuff inside. Everything else is of no importance and unfortunately the tuner makes about 90% of internals of these radios.I would like to use the parts to build a small 5-10W amp but im not sure where to start.
All vital audio parts and circuitry in these things is cheap and lofi, and modifications using the old chassis tend to be difficult. I doubt the thing will have any headroom to speak of nor even such a wonderful tone. It's a vintage radio design, not some classic guitar amp design. Keep that in mind.
Which P90 is it anyway? The push-pull or the single-ended version? Do note there were several revisions of each. Schematics can be found but make sure you get the correct ones and don't trust that they apply 100% to your unit.
If you ever get to this point I would seriously recommend that a project started entirely from scratch is a better idea. The tranformers will be the hardest and the most expensive parts to come by. If you have to swap them it's likely easier to just build an entirely new amplifier from ground up.If I need to get some new transformers I will.
As said, there are practically 3 - 4 tubes useful for audio purposes inside that thing. Everything else will go. A guitar amp doesn't need a tuner.The main issue is, the tubes are hard to come by so once they go, thats pretty much it.
If you really must make this thing guitar compatible I would first just try hardwiring the guitar input to the first AF stage. It's an easily reversible mod, won't destroy rest of a nice vintage radio (which, if I have understood right, is actually quite collectible and desired cathedral radio), and will give you an idea if it's worthwhile to further pursue the idea of converting that thing to guitar amp.
Usually those conversions just ruin a perfectly fine and valuable piece of history.
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Stevem
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- Location: 1/3rd the way out one of the arms of the Milkyway.
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I kind Of agree with Teemuk if the radios case is in really good shape, but I have to ask this question!
I live in the metro NY area and as of two years ago TV broadcast over the air waves where stopped and in the next 10 years or so a lot of radio broadcast will do the same!
In light of this what will all of these old persevered radio be good for at that point other than something else to have to dust in the house?
If it's cabinet is not in pristine condition and you are not into wood restoration than go guitar amp building with it!
Also many of these tubes that they use can be had for cheap, like on the tube world site, so be so quick to go changing the tube layout.
But either way you go you will need that isolation PT , or a normal PT !
I live in the metro NY area and as of two years ago TV broadcast over the air waves where stopped and in the next 10 years or so a lot of radio broadcast will do the same!
In light of this what will all of these old persevered radio be good for at that point other than something else to have to dust in the house?
If it's cabinet is not in pristine condition and you are not into wood restoration than go guitar amp building with it!
Also many of these tubes that they use can be had for cheap, like on the tube world site, so be so quick to go changing the tube layout.
But either way you go you will need that isolation PT , or a normal PT !
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Old Tube Radio Amp
I've done it, the chassis layouts stink though. They're designed for radio circuits, so tube positioning is suboptimal, and then there are huge swaths of dead space where the interstage transformers, tuning dials, etc, would be attached.
You can use all the tubes, but you'll find no examples how. Lots of those tubes will be remote cutoff, some will be heptodes, a lot will be microphonic pentodes. You'll need to do a ton of math and then a ton of experimenting.
If you just want to build a champ clone or something, going with a new chassis is a lot easier, skip the radio bit. If you want to build something completely unique, sure go ahead, but it is a huge ton of work. My own, I'm tearing down for the third or fourth time on a quest to improve the circuit and weed out the oscillations.
I don't believe in preserving this stuff for the sake of preserving it - they are mass-produced radios, and if the naysayers cared so much they could pick up hundreds for cheap and set up a museum somewhere. That doesn't mean that I don't think preserving radios is cool, because it is, but I don't feel they are sacred artifacts either.
You can use all the tubes, but you'll find no examples how. Lots of those tubes will be remote cutoff, some will be heptodes, a lot will be microphonic pentodes. You'll need to do a ton of math and then a ton of experimenting.
If you just want to build a champ clone or something, going with a new chassis is a lot easier, skip the radio bit. If you want to build something completely unique, sure go ahead, but it is a huge ton of work. My own, I'm tearing down for the third or fourth time on a quest to improve the circuit and weed out the oscillations.
I don't believe in preserving this stuff for the sake of preserving it - they are mass-produced radios, and if the naysayers cared so much they could pick up hundreds for cheap and set up a museum somewhere. That doesn't mean that I don't think preserving radios is cool, because it is, but I don't feel they are sacred artifacts either.
Re: Old Tube Radio Amp
Thanks for the quick response. What do you mean by AF. I have been looking over the schematic for it and trying to figure out what parts are what.
Where in here could I drop a guitar signal and get some sort of output?
http://www.freeinfosociety.com/media/images/3411.gif
And if I did, should I just disconnect everything before it in the circuit?
Thanks
Where in here could I drop a guitar signal and get some sort of output?
http://www.freeinfosociety.com/media/images/3411.gif
And if I did, should I just disconnect everything before it in the circuit?
Thanks
Re: Old Tube Radio Amp
As for the preservation, I am not a sentimental person so I have no hesitation about tearing this apart (short of someone offering me a large sum of money). I'm not expecting to get a super nice amp out of this thing either, if I did I would just get a kit or something. I'm hoping to get something that has a cool sound even if it is super distorted. I have the original speaker too (which has a transformer mounted to it, never seen that before).
If I could get it down to 2 tubes and a couple transformers, I don't mind a poor layout in the chassis. All the tube sockets are basically riveted to the chassis anyway so I'm going to work around that.
If I could get it down to 2 tubes and a couple transformers, I don't mind a poor layout in the chassis. All the tube sockets are basically riveted to the chassis anyway so I'm going to work around that.
Re: Old Tube Radio Amp
That's some sage advice there.shoggoth wrote:
If you just want to build a champ clone or something, going with a new chassis is a lot easier, skip the radio bit. If you want to build something completely unique, sure go ahead, but it is a huge ton of work. .
TM
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Old Tube Radio Amp
The easy place to try and pump some guitar signal in is at C46.
Disconnect it from the resistor that is before it and hook up your input to that caps disconnect end and the chassis.
You will likely not get much volume, so if you have a boost type stomp box to stick in front that may be a good thing.
Disconnect it from the resistor that is before it and hook up your input to that caps disconnect end and the chassis.
You will likely not get much volume, so if you have a boost type stomp box to stick in front that may be a good thing.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Old Tube Radio Amp
I hooked up my input just after C46 because C46 has 3 terminals and I wasn't sure which to disconnect. I think I could very faintly hear a sound out of the speaker but it might have just been in my head. Tubes were hot but no beans.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Old Tube Radio Amp
Why does c46 have three terminals, it only goes to two places, you sure you are at c46 ?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Old Tube Radio Amp
One can find at least three different schematics for different versions of that amp. At least one version uses a single-ended output stage while two have push-pull output stages.
There is a three-terminal capacitor in at least one of these versions but it is not the coupling cap 46 or an equivalent, it's an entirely different capacitor (tone control) one stage further in the signal path.
Have we yet even verified we are referring to correct schematics....?
There is a three-terminal capacitor in at least one of these versions but it is not the coupling cap 46 or an equivalent, it's an entirely different capacitor (tone control) one stage further in the signal path.
Have we yet even verified we are referring to correct schematics....?
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Old Tube Radio Amp
I was just going by the one he posted assuming he had confirmed a match?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
OLD TUBE RADIO AMP
When I was a kid, I bought an electric guitar with S&H Green Stamps. It took a long time to save up for the amp, so in the mean time I discovered I could go into the volume control of a radio (pre) tuned to a blank spot on the dial. I also learned about getting zapped by line current and B+ voltage! It worked pretty good. I could hear my guitar and I didn't die!
I since built an AM transmitter that uses a 117L7/M7GT tube. Now I can play guitar through any AM radio, get the sweet mojo of the whole circuit, and use as many radios as I wish. http://www.antiqueradio.org/transmitter.htm
I since built an AM transmitter that uses a 117L7/M7GT tube. Now I can play guitar through any AM radio, get the sweet mojo of the whole circuit, and use as many radios as I wish. http://www.antiqueradio.org/transmitter.htm