i have seen this done different ways adding a power supply hooking up a couple of diodes and filter caps but i've always wondered how did they used to do it? you always see an ad that says bat. farm radio has been converted to ac i've have never seen one and wonder if they added on to the chassis installed a rectifier tube and voltage devider was this a perminent modification.is there a standerd procedure for this? most bat sets have dc only tubes so you couldn't just run them with a 1.5 xformer. i'm just curious as how most shops used to do this. butch

Often people just purchase an A/B power supply such as the one www.tubesandmore.com sells. This unit supplies filtered DC for all battery set applications. Doing the conversion on your own, you have a vast assortment of ideas and methods to choose from. You can use a transformer and such. You can go the AC/DC route and use a large ballast resistor, as was done in the old 3 way portables. You could change all of the tubes over to AC type tubes, which would require some rewiring. This may also allow you to have more power from the speaker, as battery type tubes are not often known for high wattage output. If you wanted to get really technical without replacing all of the tubes, instead of using ballast resistors for the AC-DC method, you could use integrated circuitry or at least regulation transistors and zener diodes. Personally I do not like this method, as the usual failure route for integrated circuitry is for it to short and allow a lot of current through, which would blow your tube filaments. Resistors, when they go, often just open up, which would simply leave you with a dead set. Resistors don't often open up in less than a 10 year period of time.

Many 6 volt (vibrator) farm radios use AC type tubes, though not all. Some use filamentary tubes which, unless designed for the purpose, do not work well on AC. The radios that use AC type tubes may easily be converted by obtaining an appropriate AC transformer, provided that the transformer will fit on the radio chassis. The vibrator socket may then be converted to a rectifier socket, or if a rectifier was used with the vibrator, you may leave the vibrator socket alone and modify the rectifier socket instead. Of course the vibrator should be disconnected, as you don't want it to operate from the 6 volt AC supply. It was originally wired in with the filaments in most radios to operate off of a 6 volt storage battery.

With all of the methods mentioned above, if you are looking to keep the set as original as possible, you will want to build a separate power supply that will fit inside or next to the radio, that will be able to operate the radio as it was originally designed.

In the very early days of radio, stores sold special kits that would plug into all of the tube sockets of the radio. The special plugs were wired to an AC filament supply, and had sockets on top of the plugs so that the new AC type tubes could be used. A B supply could be used with the set as well to completely eliminate batteries. Since there were far fewer tubes available back then, and many battery sets used 4 pin triodes, conversion was easy for many sets. Only a few styles of conversion plugs were necessary.

Thomas

:Often people just purchase an A/B power supply such as the one www.tubesandmore.com sells. This unit supplies filtered DC for all battery set applications. Doing the conversion on your own, you have a vast assortment of ideas and methods to choose from. You can use a transformer and such. You can go the AC/DC route and use a large ballast resistor, as was done in the old 3 way portables. You could change all of the tubes over to AC type tubes, which would require some rewiring. This may also allow you to have more power from the speaker, as battery type tubes are not often known for high wattage output. If you wanted to get really technical without replacing all of the tubes, instead of using ballast resistors for the AC-DC method, you could use integrated circuitry or at least regulation transistors and zener diodes. Personally I do not like this method, as the usual failure route for integrated circuitry is for it to short and allow a lot of current through, which would blow your tube filaments. Resistors, when they go, often just open up, which would simply leave you with a dead set. Resistors don't often open up in less than a 10 year period of time.
:
:Many 6 volt (vibrator) farm radios use AC type tubes, though not all. Some use filamentary tubes which, unless designed for the purpose, do not work well on AC. The radios that use AC type tubes may easily be converted by obtaining an appropriate AC transformer, provided that the transformer will fit on the radio chassis. The vibrator socket may then be converted to a rectifier socket, or if a rectifier was used with the vibrator, you may leave the vibrator socket alone and modify the rectifier socket instead. Of course the vibrator should be disconnected, as you don't want it to operate from the 6 volt AC supply. It was originally wired in with the filaments in most radios to operate off of a 6 volt storage battery.
:
:With all of the methods mentioned above, if you are looking to keep the set as original as possible, you will want to build a separate power supply that will fit inside or next to the radio, that will be able to operate the radio as it was originally designed.
:
:In the very early days of radio, stores sold special kits that would plug into all of the tube sockets of the radio. The special plugs were wired to an AC filament supply, and had sockets on top of the plugs so that the new AC type tubes could be used. A B supply could be used with the set as well to completely eliminate batteries. Since there were far fewer tubes available back then, and many battery sets used 4 pin triodes, conversion was easy for many sets. Only a few styles of conversion plugs were necessary.
:
:Thomas

hi thomas and thanks for the reply i have a ss power supply and and old tube type which uses a 5y3 'xformer and filter caps with a voltage devider these work alright but i have a few low end farm radio's which i would like to convert to ac but i would like to do it like they used to do in the forties and fifties if however it took special sockets i guess i'm out of luck however rewiring the tube sockets and putting different tubes in sounds feasible i just wondered how it was done back then. butch

::Often people just purchase an A/B power supply such as the one www.tubesandmore.com sells. This unit supplies filtered DC for all battery set applications. Doing the conversion on your own, you have a vast assortment of ideas and methods to choose from. You can use a transformer and such. You can go the AC/DC route and use a large ballast resistor, as was done in the old 3 way portables. You could change all of the tubes over to AC type tubes, which would require some rewiring. This may also allow you to have more power from the speaker, as battery type tubes are not often known for high wattage output. If you wanted to get really technical without replacing all of the tubes, instead of using ballast resistors for the AC-DC method, you could use integrated circuitry or at least regulation transistors and zener diodes. Personally I do not like this method, as the usual failure route for integrated circuitry is for it to short and allow a lot of current through, which would blow your tube filaments. Resistors, when they go, often just open up, which would simply leave you with a dead set. Resistors don't often open up in less than a 10 year period of time.
::
::Many 6 volt (vibrator) farm radios use AC type tubes, though not all. Some use filamentary tubes which, unless designed for the purpose, do not work well on AC. The radios that use AC type tubes may easily be converted by obtaining an appropriate AC transformer, provided that the transformer will fit on the radio chassis. The vibrator socket may then be converted to a rectifier socket, or if a rectifier was used with the vibrator, you may leave the vibrator socket alone and modify the rectifier socket instead. Of course the vibrator should be disconnected, as you don't want it to operate from the 6 volt AC supply. It was originally wired in with the filaments in most radios to operate off of a 6 volt storage battery.
::
::With all of the methods mentioned above, if you are looking to keep the set as original as possible, you will want to build a separate power supply that will fit inside or next to the radio, that will be able to operate the radio as it was originally designed.
::
::In the very early days of radio, stores sold special kits that would plug into all of the tube sockets of the radio. The special plugs were wired to an AC filament supply, and had sockets on top of the plugs so that the new AC type tubes could be used. A B supply could be used with the set as well to completely eliminate batteries. Since there were far fewer tubes available back then, and many battery sets used 4 pin triodes, conversion was easy for many sets. Only a few styles of conversion plugs were necessary.
::
::Thomas
:
:hi thomas and thanks for the reply i have a ss power supply and and old tube type which uses a 5y3 'xformer and filter caps with a voltage devider these work alright but i have a few low end farm radio's which i would like to convert to ac but i would like to do it like they used to do in the forties and fifties if however it took special sockets i guess i'm out of luck however rewiring the tube sockets and putting different tubes in sounds feasible i just wondered how it was done back then. butch

This is one thing I was thinking about also, My question is, can you use a computer power supply for the A supply? These power supplies say they are rated at 9 up to 25 amp output at 5 volts, but when I opened some up they have very small transformers in them. Could they realy handle this load? of course I would have to come up with the B supply but this could be done the ac/dc way. I would think the C supply could use another output from the power supply as there are many outputs. It looks like most of the outputs use a common ground so this may be a problem. What do you think? Do you know of any website to get info on computer power supplies?
Tom

Well, in reply to Butch, you can simply leave the original tubes in place for some of the farm sets if they use the 1.5 volt filamentary tubes. Building a simple AC/DC power supply like that found in the Zenith 5G-500 and 6G-601 will work quite well. You can use ballast resistors to reduce the current to the filaments. The trick is figuring out whether the tubes can be run in series or parallel as series is ideal--minimal draw on ballast resistors. The tubes must all draw the same amperage in order to be run in series. If they were originally wired in parallel, changing the biasing for series operation is a challenge. If the filaments are wired in series, the tubes must follow the general configuration that one of the radios mentioned above follows--that is, you want the power output tube on the high end of the string so that it can take advantage of the positive filament voltage, which will aid in biasing the tube. The other tubes must follow as shown in the diagram. With the radios I mentioned above, if the filaments are wired out of order and grid resistor bias connections (IF transformer returns, etc.) are not placed where shown, the set will not operate properly.

In reply to Tom's question, the supply is not so much a computerized system as it is a simple transistorized regulator like those found in modern automobiles. A high current transistor is used along with a zener diode. A variable resistance is provided to control the amount of current fed to the diode. The diode switches on at a specific voltage. For general radio use, you'd select a 1 volt diode. The variable resistor would be adjusted so that the diode saw its switching voltage when the appropriate output voltage was seen at the tubes (from the transistor). Using a 1 volt diode would allow you to regulate down to 1.5 volts. Adjusting such a device is not as complicated as it seems, as you only need to take readings at the point which the voltage is actually being used (tube filaments). The zener diode voltage naturally occurrs where it should when your selected voltage is found, and can be disregarded. I simply mentioned it to give you an idea as to how the device functions. Increasing the resistance to the diode will lower the voltage available to it, allowing the transistor to be on for longer periods of time, allowing more voltage to the tube filaments. Once appropriate filament voltage is obtained, this voltage, fed through the variable resistor, is enough to supply the diode with one volt, which switches off the transistor. The voltage collapses and the transistor turns on again. All of this takes place over and over again in split second time (100s of cycles per second).

For my 1951 Chevrolet, I built one of these voltage regulators because I got tired of cleaning the regulator points, which never seemed to last more than a year at best. New mechanical regulators are expensive, too--from $45 to $90. To give you an idea why the regulator wears out, the points open and close from 150 to 250 times a second. The solid state regulator does this many times more with no mechanical parts. I built the regulator from a circuit I found on line. The circuit calls for a 12 volt diode for 12 volt use (13.5 charging volts). For 6 volt use it calls for a 6 volt diode (7.4 charging volts). The only diode I could find was a 5 volt diode, which works just as well, as the voltage sent to it which switches on and off the transistor is varied by a variable resistor. So long as the diode sees the appropriate voltage to cause the transistor to switch off at the voltage I desire, all is well. The system has been performing flawlessly for 2 years now. My car always regulates at 7.4 volts.

As for the transformer, if it is small, this does seem odd. Since it is only supplying the filaments, it only has a couple of windings, so this may be the reason for its small size. Still, at 9 amperes, the secondary is quite thick. All I can say is that if the transformer does not over heat under full load, then all is well. The transistorized circuit I built only supplies the generator of my car with about 2 to 4 amperes. The original circuit was for a motorcycle dynamo, which draws considerably less than this. I paralleled two of the required transistors for my regulator, and this seems to work well. I also added a heat sink. I probably could have gotten away without a heat sink if I added one more transistor. For your application, you will either have to find a stronger transistor or will have to parallel 4 or 5 transistors. I do not know how this affects the circuit. Seeing as the parts are very inexpensive and are available at Radio Shack, I say that you should go for it and just see what happens.

If you would like, I'll e-mail you the schematic. I do not recommend that this regulator is used with more than about 15 volts. Don't use it to regulate 110 volts down to 1.5 volts. You need special circuitry to do that. The schematic also includes a current regulator for auto use. You do not need a current regulator, so you can simply omit that part of the circuit.

Thomas
:::Thomas
::
::hi thomas and thanks for the reply i have a ss power supply and and old tube type which uses a 5y3 'xformer and filter caps with a voltage devider these work alright but i have a few low end farm radio's which i would like to convert to ac but i would like to do it like they used to do in the forties and fifties if however it took special sockets i guess i'm out of luck however rewiring the tube sockets and putting different tubes in sounds feasible i just wondered how it was done back then. butch
:
:This is one thing I was thinking about also, My question is, can you use a computer power supply for the A supply? These power supplies say they are rated at 9 up to 25 amp output at 5 volts, but when I opened some up they have very small transformers in them. Could they realy handle this load? of course I would have to come up with the B supply but this could be done the ac/dc way. I would think the C supply could use another output from the power supply as there are many outputs. It looks like most of the outputs use a common ground so this may be a problem. What do you think? Do you know of any website to get info on computer power supplies?
:Tom

Actually, here is the link to the schematic:

http://home.t-online.de/home/pravg/solidsta.htm

I must correct myself on what I said about the function of the Zener diode. Actually the zener diode is connected in a fixed way to the output voltage. What the variable resistor does is feed a varied amount of this switching signal voltage to the transistor.

Also, this regulator was originally designed to regulate the field coil of a generator. Modifications must be made for it to work in a filament supply circuit. The voltage in from the left, as shown in the diagram, is actually the output from the generator. Varying the field magnetism varies this voltage, and so the Zener diode sees the voltage it is regulating. When you use this schematic, you will be sending to the left a steady rectified DC voltage from a transformer. Because of this, modifications must be made to the circuit so that the Zener diode sees the regulated voltage and not the steady incoming voltage. The field coil in the original schematic will be your filaments (load). Instead of connecting ZD1 and R4 to the incoming positive lead as shown in the original diagram, connect them to the F lead. Instead of placing C2 where it was originally found, place it across the field terminals. Choose a high value, say 200 to 1000 MFD.

R2 was simply used in the original diagram to convert a 6 volt dynamo to 12 volts. Since the dynamo was now putting out 12 volts, it was necessary to reduce the voltage to the field coil to a maximum of 6 volts so that it would not be burned out. Omit this resistor in your circuit.

D2 was used as a cut-out diode so that current could flow from the generator to the battery, but not in reverse when the engine was shut off (generator stopped). Omit this diode.

R5, TR3, and C1 were used for the current regulation circuit. Omit these components and their corresponding wiring. You do not need them.

Build a nice full wave rectifer prior to this circuit and filter it well. Use a condenser of at least 200 MFD. You may place a small choke either prior to or after the regulator. If you place it after the regulator at F, leave C2 where I said it should go, but connect R4 and ZD1 AFTER the choke. Add more capacitance after the choke for added filtering. If you use a choke, the resistance must not be too high, or it will significantly limit the amount of current available to the filaments. If a choke is used, a transformer capable of producing 20 volts should be used so that ample power is still available (that is, if this circuit is used with anything more than 2 volt tubes). Condensers should all be rated at 30 volts or higher.

When building this regulator, test it out on inexpensive light bulbs first. Don't use your fine tubes.

Thomas

Butch: I have a 'L Tattro farm set that was converted in the past to AC operation. It is fairly well butchered, in my opinion. A rectifier tube was added along with a transformer. I keep setting it aside to work on later.

I makes much more sense, in my opinion, to use a battery eliminator than to try to convert a battery set to AC.

:Butch: I have a 'L Tattro farm set that was converted in the past to AC operation. It is fairly well butchered, in my opinion. A rectifier tube was added along with a transformer. I keep setting it aside to work on later.
:
:I makes much more sense, in my opinion, to use a battery eliminator than to try to convert a battery set to AC.

hi doug i've thought it over and i think you are right anything else i do is going to make a mess out of it .butch

::Butch: I have a 'L Tattro farm set that was converted in the past to AC operation. It is fairly well butchered, in my opinion. A rectifier tube was added along with a transformer. I keep setting it aside to work on later.
::
::I makes much more sense, in my opinion, to use a battery eliminator than to try to convert a battery set to AC.
:
:hi doug i've thought it over and i think you are right anything else i do is going to make a mess out of it .butch

One might suppose that the only reason to do such a conversion in this day and age would be for the challenge of it. In my younger and more foolish days I converted a Zenith 6V27 (6 volt vibrator type farm set) to AC operation. I added a power transformer and an 80 rectifier to the chassis, replaced the Wright-Decoster magnetic speaker with an 8 inch electordynamic, and then the fun began. The type 15 tetrodes in the RF and IF stages had to be replaced with 39/44's, and the 19 duo triode output was replaced with a pair of 41's (there were extra socket holes in the set). The job was neat and attractive, but what remained was a set that was not quite a Zenith 6V27 nor a 6S27. It is a now a piece of my personal history, but it is essentially worthless as an example of radio history. It would have been better that my time was spent in restoration of new construction. It is probably better not to undertake this operation with a dset ov ANY significance whatever.

I grew up on a farm in central Minnesota. Here is a story told to me by my dad about our Coronado console radio I listened to when I was a kid in the 40's and 50's growing up on the farm. In about 1940 or 41 my parents got R.E.A. on the farm so my dad took our radio along with some of the neighbors radios to a radio shop in St. Cloud, Minnesota about 40 miles away to have them converted to 120 volt sets. In our radio they changed all the tubes to 6 volt tubes and added a transformer. I remember 3 metal tubes with caps and 2 glass tubes. They did a very professional job in changing it and by looking at it without knowing about the changes you would never suspect that it was rewired. (I suspect that this shop, and many other radio shops did a booming business changing battery radios as REA become available to the farms.) It worked very well, receiving stations from Minneapolis/St. Paul, over 100 miles away with ease. I don't know the model number of the radio but I would love to find one like it to see how the set was originally wired.