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Voltage Pentode or Tetrode (with diode) ·Diode-Diode-Pentode

17C8

Double-diode remote-cutoff pentode designed for RF, IF, or AF amplification together with receiver detection functions.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 3
Base: -
Socket code: B9A
Base pins: -
Nominal heater: 17 V / 100 mA

Description

17C8 — Double Diode-Remote Cutoff Pentode

The 17C8 is a multi-unit vacuum tube containing a remote-cutoff pentode and two independent diodes within a single envelope. Sponsored by Rogers Majestic Electronics, Ltd. and registered under JETEC release number 1865 on March 11, 1957, this tube is designed for use as a radio-frequency (RF), intermediate-frequency (IF), or audio-frequency (AF) amplifier.

Mechanical Specifications and Pinout

The 17C8 features a T6 glass bulb and utilizes an E9-1 base with a 9T RETMA basing designation. The tube is constructed with a coated unipotential cathode. The pin connections are assigned as follows:

Pin Number	Electrode Connection
1	Grid No. 2 (Screen Grid)
2	Grid No. 1 (Control Grid)
3	Cathode, internal shield
4	Heater
5	Heater
6	Pentode plate
7	Diode No. 1 plate
8	Diode No. 2 plate
9	Grid No. 3 (Suppressor Grid)

Heater and Maximum Ratings

The heater is designed for series or parallel operation with a nominal voltage of 17 V and a current of 100 mA.

Heater Specifications

Heater Voltage: 17 V
Heater Current: 100 mA
Calculated Heater Power: 1.7 W (calculated as $17\text{ V} \times 0.1\text{ A}$ )

The maximum ratings are established separately for the pentode and diode sections. These limits represent the absolute boundaries for safe and reliable operation.

Pentode Section Maximum Ratings

Plate Voltage (without current): 550 V
Plate Voltage: 250 V
Plate Dissipation: 1.5 W
Screen Grid (Grid No. 2) Voltage (without current): 550 V
Screen Grid (Grid No. 2) Voltage (plate current < 2 mA): 250 V
Screen Grid (Grid No. 2) Voltage (plate current = 5 mA): 125 V
Screen Grid Dissipation: 0.3 W
Cathode Current: 10 mA
Voltage between Heater and Cathode: 150 V
External Resistance between Heater and Cathode: 20,000 ̩
Maximum Grid No. 1 External Resistance (with cathode bias): 3 M̩
Maximum Grid No. 1 External Resistance (with grid current biasing only): 22 M̩

Diode Sections Maximum Ratings (Each Diode)

Peak Plate Inverse Voltage: 350 V
Plate Current: 0.8 mA
Peak Plate Current: 5 mA
Voltage between Heater and Cathode: 150 V
External Resistance between Heater and Cathode: 20,000 ̩

Direct Interelectrode Capacitances

The direct interelectrode capacitances of the 17C8 determine its performance in high-frequency circuits. The capacitance values are specified as follows:

Pentode Section Capacitances

Pentode Grid No. 1 to all other elements: 4.2 ̷̷F
Pentode Plate to all other elements: 4.9 ̷̷F
Between Pentode Plate and Grid No. 1: max. 0.0025 ̷̷F
Between Pentode Grid No. 1 and Heater: max. 0.07 ̷̷F

Diode Sections Capacitances

Between Diode No. 1 Plate and Cathode: 2.2 ̷̷F
Between Diode No. 2 Plate and Cathode: 2.35 ̷̷F
Between Diode Plates: max. 0.35 ̷̷F
Between Diode No. 1 Plate and Heater: max. 0.02 ̷̷F
Between Diode No. 2 Plate and Heater: max. 0.005 ̷̷F

Cross-Section Capacitances

Between Diode No. 1 Plate and Grid No. 1: max. 0.0008 ̷̷F
Between Diode No. 2 Plate and Grid No. 1: max. 0.001 ̷̷F
Between Diode No. 1 Plate and Pentode Plate: max. 0.2 ̷̷F
Between Diode No. 2 Plate and Pentode Plate: max. 0.05 ̷̷F

RF and IF Amplifier Operating Characteristics

When operated as an RF or IF amplifier, the suppressor grid (Grid No. 3) is connected to 0 V. The remote-cutoff characteristic of Grid No. 1 allows for automatic volume control (AVC) or manual gain control over a wide range. Typical operating conditions under three supply voltages are detailed below:

Parameter	Condition A	Condition B	Condition C
Plate and Supply Voltage	200 V	170 V	100 V
Grid No. 3 Voltage	0 V	0 V	0 V
Grid No. 2 Series Resistor	68,000 ̩	47,000 ̩	47,000 ̩
Cathode Resistor	295 ̩	295 ̩	295 ̩
Grid No. 1 Voltage	-2 to -31.5 V	-2 to -26.5 V	-1.15 to -15.5 V
Plate Current	5.0 mA to —	5.0 mA to —	2.8 mA to —
Grid No. 2 Current	1.75 mA to —	1.75 mA to —	1.0 mA to —
Transconductance	2200 to 22 ̷mhos	2200 to 22 ̷mhos	1900 to 19 ̷mhos
Plate Resistance	1.0 to >10 M̩	0.9 to >10 M̩	0.9 to >10 M̩
Amplification Factor ( $g_2$ to $g_1$ )	18	18	18
Equivalent Noise Resistance	6,200 ̩	6,200 ̩	4,600 ̩

Resistance-Coupled AF Amplifier Operation

The pentode section of the 17C8 can also be configured as a resistance-coupled audio-frequency amplifier. It can be operated either in a standard pentode connection or in a triode connection where Grid No. 2 is tied directly to the plate.

Microphonics Considerations

In circuits incorporating a loudspeaker with an acoustical efficiency of 5%, the 17C8 can be utilized without special anti-microphonic precautions, provided that the input voltage required to produce a 50 mW output from the power stage is greater than 25 mV.

Pentode Connection Operating Points

Under a pentode configuration, the operating parameters for supply voltages ( $E_{bb}$ ) of 170 V and 100 V are as follows:

$E_{bb}$ (V)	$R_p$ (M̩)	$R_{[g2](/tubes/G2)}$ (M̩)	$R_{g1}$ (M̩)	$R_k$ (̩)	$R'_{g1}$ (M̩)	$I_p$ (mA)	$I_{[g2](/tubes/G2)}$ (mA)	Voltage Gain ( $E_o/E_i$ )	Distortion (%) at $E_o$ (r.m.s.) = 3V / 5V / 8V
170	0.22	0.68	1	2700	0.68	0.56	0.20	85	1.2 / 1.5 / 1.8
170	0.10	0.27	1	1000	0.33	1.25	0.50	70	1.2 / 1.6 / 2.0
170	0.22	0.82	10	0	0.68	0.56	0.19	140	0.8 / 1.0 / 1.4
170	0.10	0.33	10	0	0.33	1.16	0.46	100	0.8 / 1.4 / 2.0
100	0.22	0.68	1	2700	0.68	0.32	0.12	82	1.4 / 1.9 / —
100	0.10	0.27	1	1000	0.33	0.73	0.29	67	1.4 / 1.8 / —
100	0.22	0.82	10	0	0.68	0.32	0.11	100	2.8 / 3.0 / —
100	0.10	0.33	10	0	0.33	0.66	0.25	70	1.7 / 3.2 / —

Triode Connection Operating Points

When Grid No. 2 is connected to the plate, the pentode section behaves as a triode. The operating characteristics under this configuration are:

$E_{bb}$ (V)	$R_p$ (M̩)	$R_{g1}$ (M̩)	$R_k$ (̩)	$R'_{g1}$ (M̩)	$I_p$ (mA)	Voltage Gain ( $E_o/E_i$ )	Distortion (%) at $E_o$ (r.m.s.) = 3V / 5V / 8V
170	0.1	1	1800	0.33	1.25	11	2.1 / 3.5 / 4.8
170	0.047	1	1800	0.15	2.4	11	1.8 / 3.1 / 4.6
170	0.1	10	0	0.33	1.4	14	2.5 / 3.8 / 5.0
170	0.047	10	0	0.15	2.8	14	2.1 / 3.4 / 4.7
100	0.1	1	1800	0.33	0.74	11	3.2 / 4.9 / —
100	0.047	1	1000	0.15	1.4	11	3.0 / 4.8 / —
100	0.1	10	0	0.33	0.8	12	3.0 / 4.7 / —
100	0.047	10	0	0.15	1.5	12	3.0 / 4.8 / —

Qualitative Curve Analysis

The electrical behavior of the 17C8 is characterized by several key relationships:

Plate Current vs. Grid No. 1 Bias: The transfer characteristics exhibit a smooth remote-cutoff behavior. For plate voltages ranging from 100 V to 200 V, the plate current decreases gradually as the negative bias on Grid No. 1 is increased, extending down to a cutoff region near -40 V.
Transconductance vs. Grid No. 1 Bias: The transconductance curve confirms a wide dynamic control range. At a low bias of -2 V, the transconductance is approximately 2200 ̷mhos, which smoothly decreases to 1 ̷mhos as the bias is increased to -40 V.
Plate Characteristics: The family of plate current curves displays standard pentode behavior, featuring a sharp knee below 50 V plate voltage. A boundary curve on the plate characteristic plot represents the maximum plate dissipation limit of 1.5 W.
Grid No. 2 Characteristics: The screen grid characteristics show Grid No. 2 current as a function of Grid No. 2 voltage across various Grid No. 1 bias levels. These curves are bounded by the maximum screen grid dissipation limit of 0.3 W.

Technical Summary

The 17C8 is a versatile double diode-remote cutoff pentode housed in a T6 bulb with an E9-1 base. Designed for RF, IF, or AF amplification, it features a 17 V, 100 mA heater and a coated unipotential cathode. The pentode section offers a remote-cutoff characteristic with a transconductance range of 2200 to 22 ̷mhos under typical RF/IF operating conditions, and an amplification factor ( $g_2$ to $g_1$ ) of 18. The dual diode sections are rated for a peak inverse plate voltage of 350 V and a continuous plate current of 0.8 mA per diode. With its flexible operating points in both pentode and triode connections, the 17C8 provides a compact solution for multi-stage signal processing and amplification.

Socket description

Small-button Noval 9-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: B9A
Base pins: -
Nominal heater voltage: 17 V
Nominal heater current: 100 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: Yes

Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

3 physical sections, each with unique specifications.

Section 1

Diode

X-ray radiationInterelectrode capacitances

Max cathode current: 0.8 mA
Rectifier peak inverse voltage: 350 V
Rectifier peak forward current: 5 mA

Rogers 17C8 first detector diode of double-diode remote-cutoff pentode. Shared unipotential cathode with both diodes and pentode, using 17 V 100 mA series heater. Maximum mean anode current per diode 0.8 mA, maximum peak forward current 5 mA and peak inverse voltage 350 V. These peak values are not unconditional forward DC plate-voltage ratings. Manufacturer publishes individual capacitances.

Section 2

Diode

X-ray radiationInterelectrode capacitances

Max cathode current: 0.8 mA
Rectifier peak inverse voltage: 350 V
Rectifier peak forward current: 5 mA

Rogers 17C8 second physical detector diode, common cathode with first diode and remote-cutoff amplifier pentode. Each diode rated 0.8 mA mean current, 5 mA peak forward current, 350 V peak inverse anode voltage. Heater 17 V 0.1 A, appropriate for series string; published interelectrode capacitances. Peak current and reverse voltage limits must be kept separate from continuous current.

Section 3

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 1000000 Ω
Transconductance: 0.0022 S
Max plate voltage: 250 V
Max screen voltage: 250 V
Max plate dissipation: 1.5 W
Max screen dissipation: 0.3 W
Max cathode current: 10 mA

Rogers 17C8 remote-cutoff RF/IF/AF amplifier pentode with two detector diodes, common cathode. Maximum operating plate 250 V, plate dissipation 1.5 W, screen dissipation 0.3 W, cathode 10 mA. Screen voltage max 250 V only when plate current below 2 mA; at 5 mA plate current max screen 125 V. No-current 550 V limits are not continuous operating limits. Typical gm 2.2 mA/V and ~1 MΩ plate resistance in manufacturer 200 V plate/supply circuit with 68 kΩ screen resistor. 17 V 100 mA series heater.

Source-dependent data

Operating conditions by source

Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.

Data set 01

1959 Rogers

Published operating points and test conditions from this source.

SECTION 1

Diode

Characteristic

HeaterOrFilamentVoltage
17 V
HeaterOrFilamentCurrent
100 mA

SECTION 3

Pentode

Characteristic

CutoffCharacteristic
Remote cutoff