13CW4 — High-Mu Nuvistor VHF RF Amplifier Triode
An indirectly heated, compact metal-shell high-mu triode intended for neutralized grounded-cathode radio-frequency amplification in VHF television and FM tuners.
Overview
The 13CW4 is a high-amplification-factor Nuvistor triode intended for radio-frequency amplifier service in the VHF tuners of color and black-and-white television receivers and FM receivers. RCA explicitly specifies its use as a grounded-cathode, neutralized RF amplifier. It is electrically equivalent to the 6CW4 and 2CW4 Nuvistor types except for the heater rating.
The principal distinction of the 13CW4 is its 13.5 V, 0.060 A heater, compared with 6.3 V / 0.135 A for the 6CW4 and 2.1 V / 0.45 A for the 2CW4. The tube's compact Nuvistor construction, relatively high transconductance, and published low interelectrode capacitances suit the high-frequency front-end role described in the RCA manuals.
Nuvistor Construction and Heater
The 13CW4 requires a Nuvistor socket, rather than a conventional miniature nine-pin or octal socket. RCA describes a metal-shell Nuvistor form and provides a dedicated basing diagram. Its principal electrical construction is a single triode: cathode, control grid, and plate.
The low heater current distinguishes this member of the CW4 family. It must not be treated as interchangeable on an unchanged heater supply with the 2CW4 or 6CW4, even though RCA identifies the three as having corresponding signal-electrode characteristics.
Intended VHF and FM Applications
The RCA documentation specifies the 13CW4 for grounded-cathode, neutralized RF amplifier operation in television and FM tuner circuits. In grounded-cathode service the incoming RF signal is applied to the grid relative to the cathode, and the amplified signal is taken from the plate circuit.
Neutralization is significant because the grid-to-plate capacitance permits some electrical coupling between output and input. A neutralized amplifier arrangement is intended to counter unwanted feedback associated with that coupling, helping maintain stable operation in the VHF tuner application. The precise neutralizing circuit and frequency response depend on the receiver design and are not specified as universal values in the summarized RCA operating tables.
The stated applications include both color television and black-and-white television, as well as FM broadcast receivers. The manufacturer presents the device as a receiving-equipment RF amplifier, not as an audio output or power-transmitting triode.
Maximum Ratings
RCA gives the following Class A1 amplifier design-maximum ratings:
The 300 V plate-supply figure is conditional. RCA permits this supply voltage only where a sufficiently large series plate-circuit resistance ensures that 1.5 W plate dissipation is never exceeded. It must not be confused with a 300 V maximum operating plate voltage.
The published ratings apply at metal-shell temperatures up to 135°C. This temperature condition matters because the Nuvistor's metal envelope is part of its compact mechanical construction.
Electrical Characteristics and Operating Conditions
The RCA sheets provide two representative columns, one for typical characteristics and one for typical operation:
The amplification factor of approximately 65–68 places the 13CW4 in the high-mu triode category. Its transconductance, approximately 9.8–12.5 mA/V at the published points, is comparatively high for a receiving triode.
The familiar small-signal triode relationship μ ≈ gₘ × rₚ is consistent with the tables: 0.0098 S × 6,600 Ω ≈ 65, and 0.0125 S × 5,440 Ω ≈ 68.
RCA also gives an approximate −4 V grid voltage for a plate current of 10 µA under its specified characteristic condition. This is a useful indication of the grid-bias region associated with near-cutoff current, not a universal cutoff value independent of plate voltage.
Direct Interelectrode Capacitances
The RCA receiving-tube data give approximate capacitances:
These figures are relevant to the input and output tuning of a VHF RF amplifier and to unwanted coupling between grid and plate. In particular, the grid-to-plate capacitance explains the manufacturer's explicit reference to neutralized amplifier service.
The grouped capacitance definitions should be retained when comparing them with measurements that isolate only two electrodes.
Related CW4 Heater Variants
RCA describes these as corresponding Nuvistor high-mu RF amplifier triodes, with heater ratings being the distinguishing specification. Their different heater requirements must be respected in receiver maintenance or replacement.
Technical Summary
The 13CW4 is a 13.5 V / 60 mA high-mu Nuvistor triode for grounded-cathode, neutralized VHF RF amplification in FM receivers and color or monochrome television tuners. It offers an amplification factor of approximately 65–68, transconductance of approximately 9,800–12,500 µmhos, plate resistance of approximately 5.44–6.6 kΩ, and 1.5 W maximum plate dissipation.
Its compact metal-shell Nuvistor form, low heater current, published interelectrode capacitances, and specialized VHF tuner application distinguish it from general-purpose audio triodes. The 2CW4 and 6CW4 are closely related electrical versions with different heater ratings.
