Wunderlich refers to a series of vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

s introduced in the early 1930s. Wunderlichs were designed to be used as full-wave detectors

Detector (radio)

A detector is a device that recovers information of interest contained in a modulated wave. The term dates from the early days of radio when all transmissions were in Morse code, and it was only necessary to detect the presence of a radio wave using a device such as a coherer without necessarily...

 in AM

Amplitude modulation

Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...

 radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 receivers. However, because of their unusual design, they were rarely used in commercially manufactured receivers. The tube is named for its inventor, Norman Wunderlich.

Structure

The Wunderlich tube is a twin medium-mu triode

Triode

A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...

. The tube has two identical control grids that operate in tandem with a common heater, indirectly heated cathode

Cathode

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

 and plate.

Function

Typically, the two grids are connected to opposite ends of the center-tapped secondary of the final IF

Intermediate frequency

In communications and electronic engineering, an intermediate frequency is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called...

 transformer. The center tap of the secondary is then connected to ground through a parallel-connected resistor and capacitor circuit. This causes the tube to act as a full-wave grid leak detector. In some circuits, the center tap also provides AVC

Automatic gain control

Automatic gain control is an adaptive system found in many electronic devices. The average output signal level is fed back to adjust the gain to an appropriate level for a range of input signal levels...

bias voltage to the converter and/or IF amplifier. Some Wunderlichs, like the Wunderlich B, have a diode plate or a second grid that provide AVC bias voltage.

External links

• Schematic of the Mission Bell model 19 car radio. One of the few radios produced in the United States to use a Wunderlich detector (type 70).
• Radiomuseum.org discussion page about Wunderlich tubes.
• Vacuum Tubes Inc. article about Wunderlich tubes.