The 6E3P is the Russian version of the EM84 tuning indicator, or voltage indicator. This type of valve was used to display the optimum tuning point of a receiver, or the recording level of a tape recorder. The main benefit in reception was for FM radio where the exact tuning point was harder to determine than for AM.
This valve is in a standard thin glass tube envelope with a phosphor strip on the inside of the glass. The electrode structure is, like all such tuning indicators, based on a double triode with common cathode. The anode of the second triode is called the target and within the electron stream is a deflector electrode designed to alter the path of the electron beam, it would normally be connected to the anode. In the EM84 the quiescent condition was two green bars, one at each end of the window. As the signal strength increased the bars would elongate and eventually overlap to form a bright green region. The optimum point for tuning was a minimum gap.
The total column length change was 21 mm.
The heater white loops can be seen on the left. The amplifier triode grid is to the left of the heater/cathode and the target assembly to the right. The triode is horizontal.
The fluorescent screen is a rectangular patch of phosphor and produces a green display.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 61 mm tall.
References: Data-sheet & 1040. Type 6E3P was first introduced in 1959.