Kiebert Amplifiers 100 watt 300B quad

[archeus68]

Has anyone ever encountered a design like this?
Martin Kiebert was quite an engineer.
But a quad of 300B's usually generates 45 to 50 watts or so I thought.
Now the OPT was a FREED # 18777 rated at 1650 ohms 100 watts. With 200 watt peak capabilities.

Definitely a different type of design from the usual.
Plus the fact that this was designed for the BBC.

[Paul Birkeland]

Oof, 450V on the plates is rough service!

Once you leave class A1, then you can increase circuit efficiency.  This amp definitely has the chops to push some grid current too, so it can take full advantage of all that class AB2 has to offer in terms of power.  It is not surprising that they saw more than 100W out of it on peaks, but I have to laugh a little bit about running out of emission from the tubes themselves.  This would never be built commercially today though, tube life would be way too short.  There is some cool stuff to study in there though.

[Doc B.]

175mA peak draw at 450V? I hope you own a tube factory. You're probably going to be replacing a quad of 300Bs every three months. Per channel. This was right about the time the 6550 appeared, a tube much more manageable for trying to squeeze that much power out at that kind of voltage.

http://www.tubebooks.org/file_downloads/chicago_100W_amp.pdf