VALVE TYPES COMMONLY USED IN SELMER AMPLIFIERS
ECC81 PRE-AMP VALVE
PHOTOS COURTESY OF JOHN CHAMBERS, NOTTINGHAM, ENGLAND
A Military Specification ECC81 produced by Mullard.
JOHN DISCUSSES THE DOUBLE TRIODE VALVES:
Back in the days of octal bases, the best double
triodes were, 12SN7, 12SL7 and Mullard's wonderful ECC32, ECC33 range of
valves were all the go and were the ones that everybody used. At the onset
of things becoming smaller (this trend still continues in electronics today),
the B9A based valves were becoming very popular. Thanks are due again to our
Netherlands friends in the Dutch firm, Philips Gloeilampenfabrieken N.V. based
in Eindhoven; to the best of my knowledge, these guys developed the ECC81/2/3
range of double triodes as well as the EL34 and EL84.
The development of the ECC81/2/3 double triodes
was a major leap forward in the history of valves. All three of the variants
in one way or another have been used in almost every piece of valve
electronic equipment of all kinds, be it Hi-Fi amplifiers, guitar
amplifiers, TV's, radio ham/transmitter equipment, radios, tape recorders,
organs..... and the list goes on!? Open any of these pieces of equipment and
you would be hard pressed not to find one of the ECC8's? range in there:
ECC82's were used in almost every valve TV
worldwide!! What a star it is!
ECC83's have been used in virtually every Hi-Fi/guitar
amplifier ever produced too, making it 2nd behind the ECC82.
ECC81's however were less used throughout
though they almost always do tend to be be the phase inverter in almost
every guitar amplifier of which uses four output valves as the ECC81 has
better drive characteristics for this purpose.
The old octal-based range, like the 12SN7, 12SL7,
ECC32 and ECC33, had the following amplification factors respectively: 20, 70,
32, 35. whereas the ECC81/2/3 range of valves have amplification factors
respectively as follows: 60, 17, 100.
The 3 variants of the ECC81/2/3 range of valves are
also known worldwide again respectively as 12AT7/12AU7/12AX7, and are almost
always marked with both numbers.
Many of the currant valve (tube) manufacturers of
today are not only reproducing the whole range of ECC8?'s (including the older
octal ranges), but also are doing many supposed up-rated better variants of
them all! There is a lot of these variants out there and yet there is still a
high demand for the original production versions of these classic valves. I
wonder why!? Is it because, as in almost all cases, the originals are the
best!!?? I'm sure it is. Come on Mullard........... Why don't you jump on the
currant valve (tube) boom bandwagon, restart the good old British company, and
give us all your super valves again!!
- John Chambers.