TheRadioBoard

Hi All,
I found an interesting article in Italian language here:
http://www.leradiodisophie.it/Download/ ... oltage.pdf
The autor after search on properties on tubes when they are supplied with the under nominal voltage discovers the circuit shown below the document.
The filament voltage is 3V for a current of 0.1A and the best plate determined plate voltage is 13-15V with a current of 20µA.
The autor don't found a logical explanation and supposes a phenomenon of grid blocking.
With a 5 meter (15 feet) indoor antenna one can receive the principal transmitters of Chicago with an excellent volume in earphone. Selectivity is similar as other receivers and quality of sound is very good.
Can anyone do a layout of this schematic?
Best regards.
MichelB

Correct me if I'm wrong...... Doesn't a 6J5 need 6.3 volts on the heater to operate correctly?... That includes DC too.

Tubes will operate with less than their rated heater voltage. It is occasionally done with 6AL5 detector diodes for example, and apparently gives an increase in sensitivity.

When operated this way, the tube's mode of operation changes from space charge limited to thermally limited. In normal space charge limited mode, the heater is operated at full voltage, and the cathode boils off enough electrons that there is a space charge in the vicinity of the cathode, and it can supply as many electrons as the plate can take depending on plate voltage.

In thermally limited mode, the heater voltage is lower, the cathode is not as hot, and it produces a limited number of electrons. This changes the characteristics so that plate current is no longer simply dependent on plate voltage.

Yes Tubenut, it is a 6J5 tube.
Can you draw the simplest layout for this schematic?
Thank you in advance.
MichelB

Michel,

Your circuit is probably a Plate Detector circuit. Check out this article:

http://home.comcast.net/~phils_radio_de ... yneTwo.pdf

Running the heater and cathode at a low voltage probably has the same effect as adjusting the 5k pot in Phil's circuit.

_________________
Norman,
Over 30 years
as KA1GUK