What's your component removal system?

[Nowhere-Man]

I did some experimenting with filaments some weeks ago. I found a higher voltage but low current supply won't light a small bulb. Yet a low voltage flashlight battery will give off an orange glow. I suspect the very old Thirties valve filaments hardly glow at all and it's hard to imagine you needed just 2 volts to create sufficient free electrons to juice the circuit.
It's true early AC house supply wasn't constant. The battery eliminators sometimes had a primary wound for 200 volts and a house move could render a 230 volt supply. So you had the job of calculating the value of series resistor required to drop 30 volts. That's where Ohms Law suddenly got very practical.
Funny to imagine how people back then had no mobile phones or stuff we take for granted. If I ever watch a Bela Lugosi movie I always keep an eye out for the cars, phones and radio sets.

[Crackle]

I did some experimenting with filaments some weeks ago. I found a higher voltage but low current supply won't light a small bulb.

Why do you think that is? Did you measure the actual voltage across the bulb when you had the "high voltage low current supply" connected to it.

Mike

[Nowhere-Man]

Not sure I remember but it may have been either a low watt or low current transformer maybe with a resistor in series. The idea was to simply heat a filament. I wanted to better understand parallel resistances with filaments. I found larger capacity batteries at low volt outdid higher voltage but low watt supply. I may have used a simple voltage divider to find a resistor gave out 6 volts and the other 3.
I recall to being very puzzled that one side of a heater filament circuit was showing continuity between LT+ and chassis. At least with the valves out I'd have expected only LT - to be at chassis potential and LT + to simply be a direct feed to the LT + terminal. Maybe a faulty valve pin holder.
Sometimes if I have doubts I will make a simple circuit up of torch bulbs or something.

[Terry]

To minimise hum with parallel connected AC heaters, the low voltage secondary is sometimes centre tapped with the centre tap earthed, thus giving 3.15V - 0 - 3.15V rather than a single 6.3V supply.

In those cases, continuity will exist between both sides of the heater supply and earth - that would account for your findings.

[pwdrive]

"I recall to being very puzzled that one side of a heater filament circuit was showing continuity between LT+ and chassis. At least with the valves out I'd have expected only LT - to be at chassis potential and LT + to simply be a direct feed to the LT + terminal."

If it was a series connected filament valve battery receiver then don't forget that most of the filament pins will be ultimately shunted to chassis via a series chain of resistors.

Lawrence.

[Crackle]

Your high voltage supply had what is called a "high internal resistance".  It could be it actually had a resistance in series with the output, or the resistance of the transformer secondary itself was too high to allow enough current to light the bulb.
On the other hand the battery had a very low internal resistance, so although the voltage was low enough current could be pushed round the circuit by the 1.5v to ensure the bulb glowed.
When the bulb was connected to the high voltage supply, if you had measured the voltage across the bulb,   you could do a rough calculation to work out the internal resistance of the supply or battery by comparing it to the open circuit voltage of the supply or battery.
The internal resistance of a battery may be calculated from its open circuit voltage VNL, load voltage VFL, and the load resistance RL:
   

For more information on "internal resistance" see https://en.wikibooks.org/wiki/A-level_Ph...Resistance

Mike

[Nowhere-Man]

OK some interesting comments. This set where I got a continuity from the + filament to chassis was purely a battery set. One side showed no continuity but the other side read 0. Then I figured when the pins are plugged in surely there would be just the filament being heated between LT + and chassis. The grid leak resistor of course would return to LT + to stop the grid getting too negative.
I wai have an excellent 1940 book on battery radio. I am also curious as to the price of the Triodes and pentodes for the battery sets. Someone said they are dirt cheap but some say about 20 quid each. Most had 4 or 5 pins. Such radios fascinate me the most as they're Great Depression era.