6J38P

The 6J38P, marked 6Ж38П in Cyrillic, is a seven-pin miniature short-characteristic pentode intended for high-frequency, broadband voltage amplification. The data sheet describes operation up to 300 MHz: this is the stated application range, not a guarantee of gain in every circuit. The oxide-coated cathode is indirectly heated. Cathode, third grid and internal shield connect to pins 2 and 7; grid one is on pin 1, the plate on 5, grid two on 6 and the heater on pins 3 and 4.

At the data sheet's nominal point, the heater operates at 6.3 V and 190 ± 20 mA, the plate at 150 V and grid two at 100 V, with an 82 Ω cathode resistor. Plate current is 12 ± 4 mA, nominal transconductance 10.6 mA/V and internal resistance 280 kΩ. Transfer capacitance does not exceed 0.02 pF. The technical excerpt offers two RF operating points, one with plate and screen both at 120 V and a 200 Ω cathode resistor; for that point it gives 19 mA and 9 mA/V transconductance. This documented option shows why a valve parameter must always be accompanied by its operating conditions.

The documents give different limits. The bilingual sheet specifies 300 V plate voltage, 160 V screen voltage and maximum dissipations of 3 W and 0.5 W; the 400 V figure for plate and screen applies only with the valve cut off. The technical excerpt instead lists 250 V plate voltage, 160 V screen voltage and dissipations of 2.5 W and 0.65 W; for the plate it specifies 300 V at cutoff, with current no greater than 5 µA. These are requirements of the respective documents and cannot be combined by selecting the most favourable limit from each.

Further material in the data sheet includes input-resistance curves at 200 MHz and triode-connected characteristics. The pulse graphs with grid two connected to the plate concern 5 µs pulses repeated at 50 Hz, distinct from continuous operation. The sheet also specifies minimum transconductance of 6.5 mA/V over 5,000 hours, while the excerpt states a minimum life of 500 hours: a parameter criterion and a life statement are not the same thing. Documentary sources: bilingual 6Ж38П data sheet and technical manual excerpt.