The KT88 is one of the few classic audio output valves. The last valves M-OV produced after a run of 28 years (1956 - 1984) were branded Gold Lion and here this Russian tube made by Genalec carries the same branding, but this valve has been made for the modern audio market.
The basic figures given are for single ended use, but the valve is almost invariably used in push pull pairs or these days in parallel push-pull.
With an anode to anode load of 4,000 Ω and 550 Volts on the anode a pair run in ultra linear AB1 will deliver 100 Watts at 3.5% distortion. With 425 Volts on the anodes and a load of 6,000 Ω the pair will generate 50 Watts at 2% distortion. If used connected as triodes in class A and with 425 Volts on the anodes and a load a - a of 6,000 Ω an output of 27 Watts at 1.3% distortion is obtained.
The envelope proudly proclaims that Genalex are a Russian company. A far cry from the import of Eastern European valves decades ago when they were just marked Foreign.
The inner grids of this beam tetrode can be seen through the end wall of the anode.
The anode is formed from two thin sheets stitched together. The inner surfaces are bright and the outer surface is carbonised to achieve good anode dissipation. The Lion logo is also clearly visible.
The The control grid is wound on Copper supports to conduct heat efficiently to the pair of radiating fins at the top.
Not clear to see through the glass but this valve is made with a glass disc not a pinch.
The base is oversize compared to standard IO bases.
The classic envelope is 48 mm in diameter and, excluding the IO base pins, is 100 mm tall.
References: Datasheet & 1040 Type KT88 was first introduced in 1956.