Cathode-Coupled Amplifiers

[Mike H]

I was remarking to DTB last night, after we'd been messing with his 6EW7 designs, I fancied trying a cathode-coupled configuration because I don't think I've seen one actually being used in any amplifier designs I've seen. And I was wondering why not.

It's one of those 'building block' type configurations typically shown in text books, showing common cathode, cathode follower, cathodyne type follower, common grid amp, cascode, and cathode-coupled.

Only ever seen in real circuits as a long-tailed pair phase-splitter.

Only reason I can think why not is cost, manufacturers' costing departments probably can't see why an extra valve should be added that "apparently doesn't do much".

Unless amyone else can think of a reason

.

[Nick]

Though in a LTP both triodes have loads unlike the cathode follower in this circuit. The Transcendental grounded grid preamp uses such a shape, though the second triode is part of a SRPP in that its got a active load.

[Mike H]

OK so not a complete dead loss then?

I was going to use a transformer for 'RL'

Plus, I figured if a negative supply can be configured for 'Rk', then it's got more "elbow room" to work in and gain will be better.

The premise for this idea was that if RL is an interstage transformer to feed the o/p stage grid then there's no caps at all in the signal path.

An alternative to trying to DC couple stages by other means that involve some cathode(s) having to be offset to high Volts.