Antonio Vernucci wrote:
They are direct replacements but they aren't very good. K3FK had a QRO
amp with a pair of 'em a few years back and we had to resolder filament
pins on one or the other of the bottles several times. We dropped in a
set of Eimacs and the problem went away.


I had the same problem with an Eimac 3-500Z, though once only.

Tony, I0JX

I've seen it a couple of times during the time that the Eimac tubes were
manufactured. I suspect that in all of these instances, the amplifier's
cooling system was not quite as it should have been. It is much more
likely to happen in an amp which relies upon fan cooling and less likely
in an amp using the Eimac Air System sockets and chimneys.

The Chinese tubes that K3FK had problems with were of the Penta brand.

Dave K8MN