All domestic packages will be shipped via UPS. Since the USPS has become extremely unreliable, DHL will be used for all International Priority and Express packages and some First Class packages. The negative feedback around multiple sections of the amp is intended in part to mitigate the distortion of this final stage.Catalog » Transformers » Output Transformers » 2503-L This stage creates a large power boost at the expense of some distortion. Two output stages were used essentially in parallel almost certainly to get more power out. The 6V6 tubes are beam power pentodes rated for 14 W plate dissipation. This stage is meant for one thing only, which is raw power. The cathode resistors therefore are only for getting a predictable and stable DC operating point. There are cathode resistors, but they are bypassed by capacitors.
Note that both output tubes are run open loop, with not even local negative feedback. In case you're wondering, the 22 kΩ resistor at the top is likely the negative feedback path around the whole amp, although having the volume control inside the feedback loop doesn't make much sense. Probably one of the 3,4 pin secondary markings was supposed to be flipped. One of the primaries or secondaries should be flipped from what is shown. With identically balanced components, the output would always be zero. As the two transformer secondaries are shown, they oppose each other's voltage.
However, there seems to be a mistake in this schematic. You get the same power capability either way, but in series they can deliver more power into a 8 Ω load.
Wiring them in series would yield twice the voltage, but at 8 Ω. Wiring the outputs in parallel would yield 2 Ω. Note that each transformer is labeled as "4 Ω". The two transformers put out the same signal. Even though drawn as mirror images, the two tubes are driven identically. Unlike what others have said, this is NOT a push-pull stage.
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