I'm planning on building a battery radio kit, that I plan on making into an AC set through the use of trnsforers. I've found a transformer that gives out 9 volts, but I need to add a resistor to step it down to about 1.5-2 volts. What value and wattage must this resistor be? The transformer will be powering two IT4 vacuum tube filaments.
--
Not a good idea.
The thermal mass of the filament is low enough that the AC will
modulate the emission and you\'ll wind up with hum in the output, I
think.
Or do you have a wall-wart AC to DC converter with a 9VDC output
that you\'re improperly referring to as a "transformer"?
You would be better off getting a xformer that is designed for the heater voltage but if you insist, you can use that wall wart if it supplies enough current for the heaters. You need to know the current specs of the heaters when hot. All leads going to the heaters should be in twisted pairs to null unwanted noise emitting through out, near by components and even then you may have a little problem. Isolated xformers are a good idea for heaters how ever, you could also use DC but that too, would cause noise if it filtered.
--
"I\'d rather have a bottle in front of me than a frontal lobotomy"
"Daily Thought:
SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"
As I recall, the filaments in those 1T4 tubes, and the rest of the tubes used in old ac-dc portables were very delicate, and in series mode, installing a tube with the power on could blow all the filaments in the string. You would be safer to get a transformer with a closer voltage.
Yes. You have be careful not to overvoltage them. Also, the filament is the cathode in most of them and AC hum will be all over your set.
--
Steven D. Swift, novatech@eskimo.com, http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
With a low-impedance power source you might blow the filaments, but placing a resistor in series with a higher voltage will actually result in current limiting. As concerns inrush current, it might be safer than the low voltage source.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.