Hello, I recently got a zenith 4-B-131 and want to know if it is possible to covert this set to AC? I will completly recap and wire this radio first, but I was also wondering about using a 6 volt power supply, I must have hundreds of those AC to DC power supplys that were used on phones, printers, speakers or CD players. I even have some of the universal models that let me select the voltage and change tip polarity. As long as I use 6 volts DC and the polarity is correct, will these work? How many amps should it be rated for? I think this would be the easyest way to play these old farm radios with out much hassle. Your thoughts please?
Thanks
David

The power packs you have do not have enough current capability. I run my Zenith 6 volt radio with a 3 amp open frame linear power supply. I had to modify the supply by changing the zener diode to a higher value in the crow bar over voltage protection circuit. Then I could adjust the supply from its' normal 5 volt output to 6 volts without it going into overvolage shutdown. The power supply was a surplus one made by Power One corperation. You could use a lawn mower battery and hook a 6 volt trickle charger to it, but this may seem impractical. Others may have a better solution. If possible I try not to stray too far from the original design. I didn't look at your schematic so you may need more than 3 amps
MRO

I had a chance to take a look at the schematic for the Zenith radio. It says the battery drain is 1.7 amps.
MRO

Will a 6 volt lantern battery be used for testing?

You MIGHT be able to get it to run for a short while. If you could find a surplus 6 volt rechargable gell cell that would be a better choice. The gell cell will have lower internal resistance than the lantern battey so it would be able to handle the start up current. I don't know if the lantern battery would be able to start up the radio, thats why I say it MIGHT be able to start it. You would go through a lot of lantern batteries and I don't think they are cheap.
MRO

I have successfully used a 6/12 volt auto battery charger to power many vibrator type radios. Most 6.3 volt tubes can handle the slight extra voltage, since they were also used in autos, which use a 7.4 volt charging system. The #15s are what I'd be worried about, though. Be sure that if you use this method, the filament voltage across each is where it should be (something like 2.0 volts...I forgot). If you don't like this, best to stick to batteries. You can purchase a fine 600 c.c.a. battery at Batteries Plus for only $45. I use one in my car all the time. It'll start my car in 10 degrees below zero. You'll still need the 6 volt battery charger, though.

Thomas

If you want to go with the battery method here is some information. I Did a quick search on the internet at Home Depot and found 6 volt 4 amp hour for $18.99 Panasonic ES4-6 (about 2 hours playing time), 7 amp hour $22.95 Panasonic ES7-6 (about 4 hours playing time), 12 amp hour $29.99 Panasonic ES12-6 (about 7 hours playing time). You would have to make or purchase a charger. You could also make an unregulated power supply to run the radio. Check at the library and see if they have any ARRL manuals. There is a lot of great information in those books.
MRO

Mark and Thomas thanks for all your help, I am also looking into getting a Heathkit battery elimnator.
David

Battery eliminators are usually made for radios that have A and B batteries (and possibly C batteries). That is, they are meant for radios which have a battery for the filaments and then a high voltage battery (67, 90, or some other high voltage) for the plate circuits. You want a supply that'll supply between 6 and 7 volts for this radio. Ideally, since it isn't an automotive radio, and isn't meant to be operated from an automotive generation system (which usually charges around 7 volts), you probably want a supply that puts out between 6 and 6.5 volts. 6 would be what a fully charged stand-alone auto battery puts out (usually these radios were used with lead acid batteries). 6.5 will give you a bit more power to the tube filaments (and to the B circuits, which are flexible). The tube filaments are actually designed for 6.3 volts, so 6.3 to 6.5 will be ideal. They work well at 6 volts, though, which is why they could be used successfully with a stand alone 6 volt battery. I say stand alone because when it's connected to a charging system, it's usually receiving 7 volts, and therefore would also be putting out about 7 volts. Actually, when a battery is in a good automotive charging system, it isn't actually what is supplying the lights and accessories. A good charging system has enough to put into both the battery and the accessories, but when the battery is connected to the charging system, you will see 7 volts on the battery...this is what I mean.

Thomas

Hello, the battery eliminator that I am going to use can be switched between 6 or 12 volts with a fine and courese ajustment to dial in the need voltage and comes with a volt meter and amp meter to allow me to monitor them while powering up the radio. When in the 6 volt position you would not be able to apply no more than 6 volts thus eliminating the chance of frying anything due to over voltage. I am also going to incorperate a line fuse on the negative side of 1.75 amps not to allow any surge in power to destroy any tubes or capacitors. According to the the schematic the radio will only draw 1.7 amps during operation. Therfore I feel that the Heathkit battery eliminator would be the safest and most effective way to power my radio.
Thanks
David

You may also want to consider puting a noise filter on the output of the power supply. You could use one of those designed for ignition noise for car radios. This radio has a vibrator power supply and can impose a certain amount of noise (hash) on the power supply. This noise can feed back into the power supply and could POSSIBLY cause some regulation problems. It is possible that the supply you are getting already has this designed into it. There is an inductor and capacitor on the input of the radio and hopefully it will take care of the noise but it may not be enough. Of course I could be paranoid. Just monitor the input voltage and verify that it remains stable. As a side note, when you finally get this radio operating there will be a slight amount of hum from the speaker. This hum is normal with vibrator type radios. Sometimes my Zenith's vibrator gets stuck so I just ping it with my finger and it takes off (highly technical I know).
MRO

Thanks, That is a great Idea, I guess one out of a 12 volt system used for spark plug noise used on most of the 60's models would work fine.
David

Sounds like the perfect eliminator for your radio.

Thomas

:Hello, the battery eliminator that I am going to use can be switched between 6 or 12 volts with a fine and courese ajustment to dial in the need voltage and comes with a volt meter and amp meter to allow me to monitor them while powering up the radio. When in the 6 volt position you would not be able to apply no more than 6 volts thus eliminating the chance of frying anything due to over voltage. I am also going to incorperate a line fuse on the negative side of 1.75 amps not to allow any surge in power to destroy any tubes or capacitors. According to the the schematic the radio will only draw 1.7 amps during operation. Therfore I feel that the Heathkit battery eliminator would be the safest and most effective way to power my radio.
:Thanks
:David