The last two design examples used chokes. The chokes served two purposes. The first was to allow the bootstrapping to work without being excessively loaded. The second was to filter the power supply noise from the driver stage. The chokes work well in both functions, but could be replaced by resistors. The main disadvantage to the resistor is that it, unlike the choke, displaces voltage. Making the resistor smaller in value helps preserve the driver's share of the precious B+ voltage, but at the cost of loading down the output stage. Still, eliminating the chokes would be desirable, as good chokes are as hard to find as good audio transformers.
   
Direct Coupled Accordion
    In the circuit below, we have regained the cathode resistor bypass capacitors and lost the chokes and bootstrap capacitors along with the coupling capacitors. Definitely a shopping list of pluses, but what did we have to pay for it?

     The price paid is the inclusion of the negative power supply. Negative power supplies are as popular as Mylar coupling capacitors to many tube fanciers. Why? The usual culprits in human affairs are fear and ignorance (greed can be seen as a subset of fear). Many fear complexity; it intimidates. For many the great advantage that tube electronics holds over its solid-state alternative is simplicity. The motto of many audiophiles is "The simpler the better (even if the circuit doesn't work as well)." This explains the overly minimalistic approach to engineering that has become so popular, particularly on the Internet. Grid-stopper resistors, grid resistors, fuses, protective diodes--all have been removed to further the cause of simplicity. The most common failing of a circuit that warrants sending me an email begging for help is oscillation. My answer is to add a grid-stopper resistor -- and the usual reply is "Aren't grid-stopper resistors bad?" Yes, to some extent all components are bad, but oscillation is worse, particularly if it takes out your power amplifier and loudspeakers. And certainly negative power supplies subtract from the simplicity these audiophiles desire. The second culprit is ignorance. Many do not understand how a negative voltage is possible at all; isn't that like saying that someone is negative six feet tall? But since the readers of this journal are both brave and informed, we can move forward.
      In the circuit shown above, the output tubes are directly coupled to their driver tube's plate. This practice usually runs the risk of damaging the output tubes at turn-on, as the output tube's grid often must see the full B+ voltage until the unit warms up. But in this example, the output tubes are protected somewhat by being in series with each other, as current can flow through either tube only when both tubes are hot and conducting. Furthermore, even if the driver tube is yanked from its socket while the amplifier is in use, the output tubes can only see their grid climb to the same voltage as their cathodes, not the full B+ voltage.

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