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KT66

Sensibly equivalent to:
6L6G CV1075 EL37 PP60 VT75
See also:
Osram Advert, December 1947 - Osram Advert, December 1952 - Osram KT66 Advert - Some Important British Valves - Brimar 25P1 Amplifier - The Williamson Amplifier - Osram KT2, KT76, KT33C, KT66, KT61, KT66, PX4 & PX25 Advert - Osram KT2, KT63, KT61, KT66, PX4, U50, KT76, KT33C, KT71, U76 & U31 Advert - Osram Valve Range Advert - Osram Audio Output Valves Advert - KT66 and KT88 Advert
    
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The KT66 is a very well known audio output beam tetrode valve. This exhibit has a black base cap and the classic shouldered envelope shape. This suggests a pre-war build. The adverts from the 1940's and 1950's show the later straight sided envelope.
The KT66 was essentially a 6L6 redesigned with a larger cathode and a shorter, fatter anode. The KT66 had less rapid acceleration, longer electron paths, and almost no kink. It was ace for audio hi-fi but the electrons took longer to reach the anode and were more open to influence from magnetic, etc, fields on the way. Moreover, under HF conditions the electron stream was not perfectly in phase with the grid signal and this resulted in a loss of output power if used for RF applications.
The figures given are for single ended use, but a pair run in ultra linear AB2 push pull will deliver 50 Watts with 2% distortion.
The Osram paper label. The lozenge containing the Type identification was M-OV and the branding consisted of which paper label and box came next on the production line.
The smoked glass obscures the electrodes but the copper control grid support can be seen as can the cooling fin attached to it.
The classic envelope is 56 mm in diameter and, excluding the IO base pins, is 123 mm tall.
References: Datasheet, 1004, 1005 & 1040. Type KT66 was first introduced in 1937.

 

Pin Connections
IO
1
2
3
4
5
6
7
8
m
h
a
g2
g1
nc
h
k,bp

 

Absolute Maximum Operating Conditions
Beam Tetrode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
Pout
D
6.3
1.27
250
250
-15
85
6.3
22.5k
6.3
7.25
9%
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated October 14, 2016.
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