Voltage Radio Detector Converter ·Heptode
Variable-mu heptode frequency changer for superheterodyne receivers. Its multi-grid construction combines oscillator and mixer action, translating incoming RF signals to the receiver intermediate frequency while permitting gain control in the converter stage.
The 13PGA (also referred to as the 13 P.G.A.) is an indirectly heated, variable-mu pentagrid frequency changer developed by Cossor. It belongs to a specialized series of Cossor valves featuring 0.2 A heaters, designed primarily for series-string operation in AC/DC or DC mains radio receivers.
As a single-valve frequency changer, the 13PGA combines the functions of a local oscillator and a mixer within a single envelope. This design eliminates the need for external coupling components, which are typically required in two-valve frequency-changing systems to inject the oscillator output into the detector circuit.
The 13PGA is designed to operate in series-connected heater chains, which are common in transformerless AC/DC or DC mains receivers. Its heater specifications are:
| Parameter | Value |
|---|---|
| Nominal Heater Voltage | 13 V (approx.) |
| Nominal Heater Current | 0.2 A |
| Calculated Heater Power | 2.6 W |
Calculation: The nominal heater power is calculated as: P = V * I = 13 V * 0.2 A = 2.6 W.
The 13PGA operates with separate voltage limits for its modulator and oscillator sections. The maximum ratings and variable operating ranges specified for the valve include:
| Parameter | Value |
|---|---|
| Maximum Modulator Anode Voltage | 250 V |
| Maximum Modulator Screen Voltage | 100 V |
| Modulator Grid Voltage (Variable) | -1.5 V to -20 V |
| Maximum Oscillator Anode Voltage | 200 V |
The variable modulator grid voltage range of -1.5 V to -20 V reflects the variable-mu (remote cut-off) characteristic of the control grid (grid 4), which allows for effective automatic volume control (AVC) or manual gain control without introducing excessive distortion.
In superheterodyne receiver designs, the 13PGA serves as a single-valve frequency changer. A key advantage of this pentagrid design is its inherent freedom from "whistles" (spurious responses or image interference) at various tuning points across the band. In alternative frequency-changing systems, preventing these whistles typically requires highly selective and complex aerial tuning circuits.
The conversion conductance of the 13PGA is optimized to provide stable and satisfactory performance in standard AC/DC receivers. Its conversion conductance is intentionally lower than that of its 4-volt, 1-ampere counterpart, the 41 M.P.G. (also referred to as the 41 MPG). This design choice was made because the typical receiver circuits utilizing the 13PGA cannot readily accommodate an excessively high conversion conductance without stability issues.
The relationship between the modulator grid voltage (Vg4) and the modulator anode current is highly dependent on the bias applied to the oscillator grid (Vg1). Under typical operating conditions with a modulator anode voltage of 250 V, a screen voltage of 100 V, and an oscillator anode voltage of 200 V, the following qualitative behaviors are observed:
The 13PGA is closely related to the 41 M.P.G., which is described as its 4-volt, 1-ampere counterpart. While they share similar pentagrid frequency-changing principles, the 41 M.P.G. features a higher conversion conductance and is designed for AC-only receivers with parallel-connected heaters, whereas the 13PGA is optimized for series-run AC/DC or DC applications with a 0.2 A current-regulated heater chain. These differences in heater ratings and conversion conductance mean they are not direct plug-in substitutes.
The 13PGA is a 13-volt, 0.2-ampere indirectly heated pentagrid frequency changer designed by Cossor for series-heater operation in AC/DC and DC superheterodyne receivers. By combining the mixer and oscillator functions into a single envelope, it eliminates the need for external coupling components to inject the local oscillator signal. With a maximum modulator anode voltage of 250 V, a maximum screen voltage of 100 V, and a maximum oscillator anode voltage of 200 V, the valve provides stable frequency conversion. Its variable-mu modulator grid (Vg4), operating over a range of -1.5 V to -20 V, ensures effective gain control while maintaining freedom from spurious whistles without requiring highly selective preselector stages.
Medium 7-contact
General specifications
Properties common to every published source and operating point.
Electrical assignments shared by every tube using this base designation.
No verified pinout is recorded for this base designation.
1 physical section, each with unique specifications.
Section 1
Cossor 13PGA indirectly heated variable-mu pentagrid (heptode) frequency changer for AC/DC or DC superheterodyne receivers using 200 mA series-heater strings. Nominal heater 13 V, 0.2 A. Maximum modulator-anode voltage 250 V, modulator-screen voltage 100 V and oscillator-anode voltage 200 V. Variable modulator-grid bias −1.5 to −20 V. Conversion conductance is application-specific and is not equivalent to intrinsic static transconductance. The manufacturer emphasizes single-valve oscillator/mixer operation and low oscillator pulling.
Source-dependent data
Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.
Data set 01
Published operating points and test conditions from this source.
Oscillator anode maximum voltage
200 V
Published datasheet value
Modulator grid variable bias minimum
-20 V
Published datasheet value
Modulator grid variable bias maximum
-1.5 V
Published datasheet value