The KT61 is an audio output valve and features the standard 6.3 Volt heater that was introduced from America in the mid 1930s. The KT61 forms part of a series of very successful valves from M-OV.

The KT61 is a high gain valve designed to be used with little amplification before the output device - ideal for low cost broadcast radio receivers.

The Osram brand label.

Looking up under the coating. The cathode is rectangular, the control grid has copper supports for good heat conduction. The third electrode out from the cathode can be seen as a flat tab. This shows the presence of the beam plate that substitutes for the suppressor grid in a pentode - and incidentally got round the Philips/Mullard patent.

The classic envelope is 45 mm in diameter and, excluding the IO base pins, is 103 mm tall.

References: Data-sheet, ¹⁰⁴³ & ¹⁰⁴⁰. Type KT61 was first introduced in 1939. See also 1939 adverts.

Pin Connections

IO

1

2

3

4

5

6

7

8

m

h

a

g2

g1

nc

h

k