Great find. These radios draw a little over 1 amp. I would start with resistance around 40 ohms. Should use 100 watt resistor. 40 volts x 1 amp = 40 watts.
Norm
:I can't beleive my luck. I have been messing around with a transformer out of a 90 b for my radio that is missing , and talking with a guy I met locally he had a 9p3 power supply sitting in his garage which he gave me as he had no use for it , only thing missing is the ballast to drop the voltage to 80 volts does any one know what the resistance of the ballast was for this unit? so I could replicate it would a safety cap be a alternative? any ideas ?
:Thanks
:Elton
:
Not an expert on the subject, but be careful here. I think that the best option other than a resistor would be another inductor as a voltage dropping device, or an autotransformer.
If a ballast resistor is desired, you might consider various high wattage lightbulbs, including projector bulbs, as they would have a ballast action, and would be able to handle the wattage. Ballasting action isn't necessary with today's well regulated line voltages, but is a nice feature, and can even soft-start the tubes.
Seems I saw someone selling ballasts for Majestic radios somewhere, but that could have been an old publication. ...Not sure where I saw it.
T.
I was going to suggest a series light bulb as well. Induction motors and transformers may not like a 'clipped' or half-cycle waveform. This is why a standard Triac SCR light dimmer won't make a good motor speed control or variac.
Elton,
I think I have the ballast tube and socket assembly somewhwere in the basement from an old junker set. I can email a pic if you want.
Jon.
:
I would go with Jon's ballast tube or resistor. Never use a cap or diode in series with a transformer.
A cap can actually nearly double input voltage. It could be a good way to power a 220 volt radio off 110 volts.
A diode will cause input to be seen as 30 cycles to a transformer. Most likely will destroy a transformer.
Norm
::I can't beleive my luck. I have been messing around with a transformer out of a 90 b for my radio that is missing , and talking with a guy I met locally he had a 9p3 power supply sitting in his garage which he gave me as he had no use for it , only thing missing is the ballast to drop the voltage to 80 volts does any one know what the resistance of the ballast was for this unit? so I could replicate it would a safety cap be a alternative? any ideas ?
::Thanks
::Elton
:
:Elton,
:I think I have the ballast tube and socket assembly somewhwere in the basement from an old junker set. I can email a pic if you want.
:Jon.
::
:
:
Projection bulb sounds like a good idea. If rated for 120 volt AC line need one that draws over 1 amp. Rating will have to be more than 100 watts.
Norm
::Was thinking along the line of a ballast for tube heaters. I see now this is a transformer primary. A diode or capacitor would be wrong. The projection bulb seems a good idea.
::
:I never thought about a bulb as a ballast , which is a good idea, It is simple and could be mounted in a enclosure of some type in the radio cabinet just like the original , where would one find projection bulbs and what wattage should I look for 40 watt?
:Thanks
:
You can get projection bulbs at high wattages. I was hoping you already had some to select. They cost quite a lot if bought new.
The are available here:
http://www.bulbdirect.com/
Bulbs are indentified by three letters rather than 2 numbers like dial lamps.
Using a Variac is a good way to test a transformer. Your transformer is good.
The only way to determine the exact ballast needed is to have radio operating. A variation in load will change voltage drop across a ballast.
Norm
::Elton
::
:: Projection bulb sounds like a good idea. If rated for 120 volt AC line need one that draws over 1 amp. Rating will have to be more than 100 watts.
::
::Norm
::
::::Was thinking along the line of a ballast for tube heaters. I see now this is a transformer primary. A diode or capacitor would be wrong. The projection bulb seems a good idea.
::::
:::I never thought about a bulb as a ballast , which is a good idea, It is simple and could be mounted in a enclosure of some type in the radio cabinet just like the original , where would one find projection bulbs and what wattage should I look for 40 watt?
:::Thanks
:::
::
::
:Norm, I have test run the supply with my variac and using a 2700 ohm resistor as a load for the field coil the outputs are spot on with the variac set at 90 volts , But I know nothing about projection bulbs do they come in the size that you indicate? I have run this at 120 just to see what the outputs would be , the outputs are about 100 volts higher than stated, and the filaments run about 3 volts, which is not too far off, I was wondering how much more draw could I expect when the radio is connected to the supply.
:E.
:
Seems likely that the original Majestic ballast was nothing more than a 200W lamp in a smaller bulb.
Incidentally someone mentioned soft start, but that's exactly the opposite of what a tungsten lamp does. It has a very low rsistance at room temperature; measure one and see.
It all depends on the bulb and the tubes. In the case of a 150mA #47 bulb, its thermal mass is so much smaller than a 120 volt string of 150mA tubes that it will increase in resistance to the point of burning out before the tubes even begin to light, and so a paralleling protection ballast whose resistance increases much more slowly is necessary. This is where the lamp tap of the 35Z5 comes in, as its resistance will increase about at the rate of the other tubes' heater resistances. ...And, of course, further protection is offered by using plate voltage to do part of the job of lighting the lamp, and this is never available until all of the tubes' heaters are warm and high in resistance.
Anyway, if you find a bulb that works (any bulb will do, though projector bulbs come in higher wattages than otherwise normally available), it should do the 'ballast' job well. Paint it black if you wish. 200 watt bulbs are available from your local hardware store for cheap. Projector bulbs are available on eBay for a whole range of prices.
I think someone else on here said that they actually had the appropriate ballast for this radio.
Also, as I said before, a less hot and wasteful method would be an inductor or autotransformer. You might find a 12 or 24 volt transformer whose secondary drops voltage appropriately without getting too warm. Early electric fans used this method--a choke in their base with taps and a slider switch that selected the various taps. You might also consider making your own autotransformer by wiring the primary and secondary of an appropriate transformer in series in phase, and then wire this to line voltage, and the radio across the primary. Be sure that the two windings are in phase or else you might wind up with more voltage than you want. I'm not sure what size secondary would give you 80 volts across the primary when wired in series. I will have to do some math. Another alternative would be simply a step-down transformer. The simplest method would just be a choke. The step-down transformer method would be less load-dependent, but either would work so long as the load was always constant.
T.
We use bucking transformers to reduce line voltage. How about a couple 24 volt transformers wired in series bucking line voltage. That would reduce the line by 48 volts. If too much use other filament transformers which add up to around 40.
Rating should be 2 amps for safety margin.
Norm
:Tungsten lamps do have lower resistances when cold than when hot, but the thermal mass of a 100 or 200 watt bulb is likely less than that of all of the radio's tubes in parallel, and so though the bulb may have a low resistance at first, it is more likely that the bulb will increase in resistance before the tubes do, and then drop back down as they heat. No guarantees here, though, as I have not tried a 200 watt bulb in series with my Majestic.
:
:It all depends on the bulb and the tubes. In the case of a 150mA #47 bulb, its thermal mass is so much smaller than a 120 volt string of 150mA tubes that it will increase in resistance to the point of burning out before the tubes even begin to light, and so a paralleling protection ballast whose resistance increases much more slowly is necessary. This is where the lamp tap of the 35Z5 comes in, as its resistance will increase about at the rate of the other tubes' heater resistances. ...And, of course, further protection is offered by using plate voltage to do part of the job of lighting the lamp, and this is never available until all of the tubes' heaters are warm and high in resistance.
:
:Anyway, if you find a bulb that works (any bulb will do, though projector bulbs come in higher wattages than otherwise normally available), it should do the 'ballast' job well. Paint it black if you wish. 200 watt bulbs are available from your local hardware store for cheap. Projector bulbs are available on eBay for a whole range of prices.
:
:I think someone else on here said that they actually had the appropriate ballast for this radio.
:
:Also, as I said before, a less hot and wasteful method would be an inductor or autotransformer. You might find a 12 or 24 volt transformer whose secondary drops voltage appropriately without getting too warm. Early electric fans used this method--a choke in their base with taps and a slider switch that selected the various taps. You might also consider making your own autotransformer by wiring the primary and secondary of an appropriate transformer in series in phase, and then wire this to line voltage, and the radio across the primary. Be sure that the two windings are in phase or else you might wind up with more voltage than you want. I'm not sure what size secondary would give you 80 volts across the primary when wired in series. I will have to do some math. Another alternative would be simply a step-down transformer. The simplest method would just be a choke. The step-down transformer method would be less load-dependent, but either would work so long as the load was always constant.
:
:T.
:
Elton,
So very sorry for taking this long to respond, work has been insane. I do have the ballast assembly with a good tube for a 9P6 power supply. Do you still need it?
Jon.
: