Voltage - Triode (with diode, heptode or hexode) ·Hexode-Triode
Triode-hexode oscillator-converter for superheterodyne receivers. The triode provides local oscillation while the hexode performs frequency conversion in low-current series-connected heater strings.
The Mullard TH21C is an indirectly heated triode-hexode frequency changer with a common cathode; its supplied sheet refers to TH4 for the non-heater electrical characteristics.
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.
2 physical sections, each with unique specifications.
Section 1
No fixed ratings are recorded for this section.
Mullard TH21C oscillator triode sharing an indirectly heated common cathode with its hexode mixer. The 21 V / 0.20 A heater is intended for AC/DC receiver heater strings, with heating time about 30 seconds and heater-to-cathode maximum 125 V. Electrical specifications otherwise refer to Mullard TH4 frequency changer, not the unrelated Philips TH4 thermocouple.
Section 2
No fixed ratings are recorded for this section.
Mullard TH21C mixer hexode, sharing common cathode with oscillator triode in AC/DC mains superheterodyne receivers. Nominal 21 V / 0.20 A heater, 125 V maximum heater-to-cathode potential. Non-heater electrical specifications are cross-referenced to Mullard TH4 frequency changer and have not been copied from an unrelated TH4 record.
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.
Heater Voltage
21 V
Heater Current
200 mA
Heating Time
30 s
Maximum Heater-Cathode Voltage
125 V
Electrical Characteristics Reference
TH4 text
SuppliedSheetStatesIdenticalExceptHeaterRating