Max Holubitsky wrote:

The 6550 is an American tube, released in late 1954 by Tung-Sol, of
Newark NJ.
The KT-88 was released a couple years later, by GEC of the UK, and is
similar to the Tung-Sol 6550, but has some improved specifications, and
looks different. The 6550A was introduced in the early 1970s, but GE of
the USA, and improves upon the specifications of the original 6550 to
the point where it is equivalent to the KT-88.

Most of the 6550 tubes on the market today, are 6550A equivalents, and
can be interchanged freely with the KT-88.

And afaik, after testing, EH 6550, EH KT88, Sovtek 6550, and Sovtek KT88
now have identical electrode structure within, and the same electrical
properties,
and only the cosmetics of the glass envelope and lettering is different.

Patrick Turner.



"N. Thornton" wrote:

6550 is what we know as KT88 - for any other non US reader.

Regards, NT