Old Tube Radio as an amp?

[mistermullens]

I'm sure I'm not the first to think of this, but I was wondering if I came across an old Tube Radio, could I use it for an amp? Like a practice amp? Is this feasible? Would a lot of mods be involved?

Here's a cool video I found.

 

[jhundt]

I think you should treat a cool little old tube radio with the same love and attention that you would give to a cool little old tube guitar amp. Don't "mod it" into something it ain't - restore it to its original glory.

 

[muchxs]

Yeah, great. Three minutes of a locked camera and we have no idea whether or not that tone is coming from that radio or not. Let's see a gutshot.

YES many vintage radios contain most of if not all of the correct parts to be converted into a guitar amp. It's one of the first conversions I attempted back in the '70s when I was young and naive, I embarked on the endeavor with no documentation and no clue. My victim was a late '40s Philco tabletop radio. I was shall we say in the steep part of the learning curve, I managed to quickly find out firsthand that there was high voltage available everywhere in that thing. I managed to achieve memorable if not fatal electrocution from nearly all available voltage sources in that chassis. Eventually by trial and error I clipped on to a point where the radio weakly amplified my guitar.

I'll pass along a few tips: Converting old radios to guitar amps is the advanced program. It's much easier to start with something intended to be a guitar amp. It's necessary to be able to cull likely donors from unlikely donors. You want a power transformer and an output transformer. If you don't see two transformers PASS on that one. If you see 50C5, 25L6, 35L6 or 50L6 tubes PASS on that one. Fair warning, ignore it at your peril!

Next, how old is the radio? Prior to around 1955 the line voltage was 110 volts not 117. In some areas the juice is as high as 125 volts. I like to start with iron that's close to correct, I don't like my filaments to be 10% too high from the get-go.

A lot of '50s radios use electrodynamic speakers. If you don't know what that is or how to deal with it this isn't a project for you.

Don't butcher anything that's valuable as a collectible. I don't like seeing tweed amps that were painted black in years gone by, I hate seeing pre-CBS Strats that were hacked for a Floyd and a humbucker back in the '80s. The antique radio guys will hold you in similar regard if you cut up a valuable old radio.

 

[Barz]

Never thought of that. It's pretty cool but, is that not a guitar amp directly to the left of that radio. Which by the way doesn't look to be ON. But then again I'm not an expert. But I have owned a couple old tube radios.

 

[klast]

I'm sure I'm not the first to think of this, but I was wondering if I came across an old Tube Radio, could I use it for an amp? Like a practice amp? Is this feasible? Would a lot of mods be involved?

A friend of mine is a bit of a "tubeoholic" and likes to tinker with old tube driven devices. When we rehearse in a small setting, without drums, he has been using at least two different radios (with stock built in speakers) and one old cinema amplifier.
Mostly sounds fairly good. Don't know how much he has modded them, though.

He's in the process of modding my first gramophone amplifier, a 2 x 2 W Philips from the early 60s. So far, the output is a bit low and it breaks up too early (!).

Klas

 

[Guitar_Ninja]

Well I know what to get the guy in the video for Christmas: a metronome.

If it was me I'd probably restore an old radio like that and then sell it for a tidy profit.

 

[pchilson]

This is an old Airline AM/FM/Phono that I fixed up, and added a 1/4" input jack (to the right of the tuning dial). Turning the selector to phone you could use it as a guitar amp. It has a 5x8 oval speaker, about 3-5 watts output, single 6V6. It was a good radio...
It is long gone now. I had fun with it.

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I also had an old Admiral console AM/phono that I did the same with. That one I put in a 12" speaker and was a 2x6K6 amp about 8 watts output. That one is long gone as well. It was in dreadful condition when I got for $10
I put the 1/4" jack in the rear of the chassis, not visible in pic

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[pango_twango]

And now for a contrarian view....Get an isolation transformer, install it correctly, and have fun. It's an easy project, the tubes are dirt cheap, and (with the proper precautions, including the Iso tranx), no more hazardous than working on a tube amp. If you seek out a model that has an "aux" or even "phono" jack on the back, you're halfway there.

Worried about destroying a 'classic'? I wouldn't be. Old tube radios are often so cheap on eBay that you'll spend more on shipping than the item itself. Some of the 'console' tube radios (and stereos) have decent preamp sections, complete with 12ax7s, etc. Stick whatever type of speaker you want on there, though the down side there is that a lot of the radios had super low impedance (e.g., 1.4).

The big question, after you unplug your soldering iron, is whether it will sound cool. From my experience, the answer is, well, kind of. A beat up 50 dollar tube amp (of the Silvertone or worse variety) that you buy and re-cap, will sound a lot more like a guitar amp, frankly. If you're willing to tinker with one that's not working, they can be had cheap on eBay as well. You can run your guitar through the table radio, and there's tubes inside it that will light up and look pretty. But (and this is again only my experience) in the end you'll have tone that can barely keep up with an inexpensive SS amp. Kind of cool to stick on the bookshelf, but wouldn't be my vote for "I'll do this, and then I'll have a tube amp."

 

[muchxs]

And now for a contrarian view....Get an isolation transformer, install it correctly, and have fun. It's an easy project, the tubes are dirt cheap, and (with the proper precautions, including the Iso tranx), no more hazardous than working on a tube amp. If you seek out a model that has an "aux" or even "phono" jack on the back, you're halfway there.

Worried about destroying a 'classic'? I wouldn't be. Old tube radios are often so cheap on eBay that you'll spend more on shipping than the item itself. Some of the 'console' tube radios (and stereos) have decent preamp sections, complete with 12ax7s, etc. Stick whatever type of speaker you want on there, though the down side there is that a lot of the radios had super low impedance (e.g., 1.4).

Then the contrarian contrarian view: I see enough "noob needs help" threads on other forums where would-be techs get in way over their heads with builds you or I might consider simple.

When I consider the risk/benefit ratio transformerless junk just isn't worth it. They were meant to be cheap to begin with and all these years later they're still cheap. Buy and butcher a Valve Junior, it costs no more than an old radio plus an isolation transformer and there's a large and enthusiastic support network for that platform.

If anyone wants old junk with 35W4, 50C5 and 12AV7 tubes one needs to look no further than my dumpster. I'll salvage one or two small parts like Stackpole pots with '50s date codes then cut the cord off what's left and toss it. Yes I could Barnum it off on some poor unsuspecting soul via FleaBay. Yes it would demonstrate a lack of integrity on my part.

 

[Alnico Sunburst]

When I was a kid and was first asking my parents for an electric guitar, I partly convinced them with the argument that I would build my own amplifier. I have always been into tubes, and seem to always find someone discarding an old tube radio. Not so much in the last few years, but there were enough floating around in the early 90's that I had plenty of raw materials on hand. I had an old Science and Mechanics magazine from 1948 which had a bunch of modifications you could add to tube radios.

Basically, the secret for the simplest way to turn an old radio (one that works!) into an amp, is to disconnect whatever is hooked up to the middle (wiper) lug on the volume control, and connect your input to that. This mod is reversable if you just desolder the connection; you can put it back later, no harm done.

I never used an isolation transformer, but was always careful to verify with a multimeter whether or not I would get zapped if I accidentally touched a ground. This might have seemed tedious, but it was interesting to find the radios that would kill you, and why (reversing the plug in the socket could make a safe setup into a killer, or just cut down on hum ).

It was also disappointing to discover that the great majority of radios have insufficient gain to be very useful as amps. With a distortion pedal to give some boost they could be okay, but really, it's about the same as if you use computer speakers for an amp. Which is easier. And much safer.

 

[Alnico Sunburst]

I should have added that with an AC/DC set with no transformers (there are old guitar amps made that way as well. I had a Harmony which sounded AWESOME) an isolation transformer is a damn good idea because even if you had a setup which seemed safe, it would only take one failed capacitor to change the situation. Like the Hallicrafters S-38 I have. It's metal outer casing is tied to the chassis through a capacitor. Which is shorted. So when I had it sitting on top of a computer tower case one day I plugged it in to use it. I was astonished to see the tubes light up through the back of the case even though I hadn't switched it on. The circuit was completing itself through the computer case. The outer case of this radio was live.

Wooden or bakelite radios were not just for looks, they kept the chassis isolated from the user. Plugging a guitar in means you're circumventing the insulating qualities.

 

[FirstBassman]

This is an old Airline AM/FM/Phono that I fixed up, and added a 1/4" input jack (to the right of the tuning dial). Turning the selector to phone you could use it as a guitar amp. It has a 5x8 oval speaker, about 3-5 watts output, single 6V6. It was a good radio...
It is long gone now. I had fun with it.

Patrick Sweaney (a great blues guy from Ohio) has also used an old record player as an amp.
Sounds amazing.
Of course, Patrick also has killer talent.

 

[varakeef]

A fellow musician of mine has his guitar plugged into phono input of an old tube radio. No mods, works like a charm.

 

[pchilson]

Patrick Sweaney (a great blues guy from Ohio) has also used an old record player as an amp.
Sounds amazing.
Of course, Patrick also has killer talent.

Well, I lack on the killer talent part...
The radio/phono worked no problem with the input jack and running a guitar through it. Problem was, not really a problem but what made it unsuitable was its a radio and therefore designed to minimize distortion. Not what you'd want in a guitar amp. It was fun and it did sound ok for what it was, it just wasn't what I had envisioned for it. The same was true for the Admiral even thought the output was higher and it had a larger speaker. Like I said, they were good radios...

 

[Jay Low]

A fellow musician of mine has his guitar plugged into phono input of an old tube radio. No mods, works like a charm.

I've done the same, too. Just cut the other plug off the guitar cord and replaced it w/ banana connectors to connect into the radio's phono input. Sounds lovely, I'm normally using a graphic EQ to boost and enhance the signal a bit.

VaraKeef, does your friend by chance have an old Finnish ASA radio, too..? ;-)

 

[jefrs]

Many old radio had a phono input. But beware, depending on the age of the instrument, they were built to very different safety standards to now, for example - live chassis. Ouch!
I've been advised regarding my two old radios (including the one with the live chassis and floating earth) that unless they work and have good cases, they are of no value even to collectors. There were so many of these domestic appliances made, far outnumbering any number of guitar amps, that even good ones have no great worth: sympathetic modification therefore acceptable. At best you have a novel guitar amp, at worst, a nice case and chassis for a home build.

 

[Alnico Sunburst]

As soon as I get the pictures thing figured out I'll post a couple of the amp I am (hardly) working on currently. I had an aluminum chassis routed out from dimensions on the AX-84 site, but didn't realize how proportionately out of whack it was as a guitar amp chassis until I saw in the flesh that it has a footprint like a VCR. A week and a half after it was cut, I'm driving down the street when out of the corner of my eye I see a flash of veneer, chrome and grill cloth. I go back, and on top of a dumpster is an empty wooden case from a late '40s GE radio / phonograph. No chassis inside. I get it home, and open the lid, and coincidentally, the too-deep chassis I made is just about perfect.

Useless without pics, I know. I'll be back in a bit...

 

[unbridled]

I think it's a cool idea as long as you're not ruining something super collectible. I've seen a couple of people do it but have never seen it done well.

 

[Alnico Sunburst]

This is the chassis I routed using a layout I found on the AX-84 site. I didn't really know exactly what I was going to make, so there are some extra holes in it that might not get used. The plans were in .PDF format, (hello, .DXF anyone?) so to transfer it to MasterCam I had to print them out full size, and then digitize it on a tablet by hand. Then I toolpathed it, and had it cut on a Fagor CNC router out of scrap .080" aluminum. The guys on nightshift were kind enough to put the flanges in on the CNC brake.

This is the empty radio cabinet I found afterward. Late '40s? Early '50s? Don't know.

So I flip open the lid and what do you know? It's actually wide enough to hold this chassis. What a coincidence!

There will be problems, natch. The holes I added for potentiometers, pilot light, etc. are now useless. I will have to figure something else out for the controls. And that chrome bezel for the frequency dial - what to do with that? But it's a start. I have a similar unit from 1945, shown here for styling comparison. Art Deco, much?

 

[cg73cmc]

Well you can convert a radio into a guitar amp but what you're going to be left with is a radio "chassis" and "shell" that has a lot of guitar amp components mounted on the inside - not to mention a guitar jack installed on the outside.

Much better - if you want to do this - just go and buy an old broken radio with no components on the inside and then go from there. What you end up with is going to be the same I think. Radios have components that guitar amps don't use - radio frequency de-modulation circuits is one of them. You can try to figure out which components you can use to make an amp - and rewire them but ... why?

It's a novel idea though but I would go for the "almost from scratch" method and just get an old chassis and see what you can do.

EDIT: This thread reminds me of the story about the creation of Brian May's "Deacy Amp". It's said John Deacon (Queen Bassist) found an old amplifier circuit board in a dumpster which he thought came from a cassette player or radio. Anyway - he built a small practice amp with it which eventually became a famous part of Brian May's guitar sound.