On Tue, 13 Mar 2001 08:59:25 -0000, Talbot Andrew
<[email protected]> wrote:

Sorry, I confused you all and remembered the wrong device.  The valves
are E55L Pentodes.   (E88CC is a doube triode, sort of ECC88 then they
ran out of numbers! )

I don't think running out of numbers is the reason for these strange

At least the Siemens Taschenbuch 1964 lists the ordinary xxnn
(x=letter, n=digit) types as "standard receiving and amplification
tubes", while the xnnx and xnnxx style tubes were listed under
"special tubes", some of which were assosiated with the Reliability,
Long life, Tight tolerance, Vibration and shock proofed and/or Cathode
free from interface attributes.

The first digit usually defined the base, thus 3n, 3nn were Octal, 8n,
8nn, 8nnn were Noval and 9n, 9nn Miniatur. However, 13n, 23n could
also be Octal and 18n, 28n could also be Noval.

So I do not think the reason for going to xnnxx format is simply due
to running out of xxnn, xxnnn numbers.

FETs are much easier to understand - wonder if a solid state version has
been produced yet ?

Are you referring to Fetrons, which appeared around 1972 and had the
same base connection as the tube counterpart and you  could just swap
the corresponding tube with this high voltage FET ?

Paul OH3LWR