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RE: Octals-med mu, low plate R

Posted by tube wrangler on January 3, 2017 at 21:44:26:
7788, connected triode, should give you
excellent performance.

There is a tendency to assume that when a tube oscillates,
it is the TUBE'S fault. It is usually a result of too much
internal wiring, wiring too long, and wiring too close to another
wire, or a component-- or wiring laced together-- THE WORST thing you can do!.

NEVER bundle ANY wire in with another wire! Remember all
those fancy pictures of spic & span Military and Ham Radio
construction-- all those wires neatly laced together with string?

This is exactly how NOT to build audio equipment. Make every wire separate from
everything else, and separate from any other wire. The farther apart they are, the better the results. Keep wires SHORT-- VERY short.

If you must run a wire across another wire, do it at right angles only.

Work in all 3 dimensions-- you can use silicone products or other
ingenious methods to have components and wire stay where it belongs...

If you get these layout principles right, you will stop unwanted oscillations because you will stop injecting unwanted signals into
the tube that is oscillating....

The use of a "grid-stopper" series resistor is sometimes used on
a tube's grid to damp-out oscillation. Use of this device-- of any
value-- is a sure-fire way to throw away most of an amp's fidelity.

Instead, use the tubes that others are afraid of because they sometimes
find them oscillating. These sound wonderful because they really respond to signal-changes-- they don't damp-out musical expression.

To keep them from oscillating, build the entire amplifier right.

The 7788 should be really good in this application. There is an article,
and discussion on using this tube as a driver, in the old Sound Practices literature-- the "B-52" S.E. amp.

The guy is pretty smart-- why not learn from him?

---Dennis---