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The RCA Datasheet is Wrong

Thanks to everyone who provided info on this. I got tired of guessing, so I built it. My circuit has a pair of 6L6GCs driven by a 6SN7 cathodyne splitter. Anode voltage is +360V, just like the datasheet. The screens are a little high at +340. At the datasheet's suggestion, I'm using a 250 ohm cathode resistor, bypassed and shared by both tubes. I measure just slightly more than +25V on the resistor, indicating 100 mA zero-signal plate current.

The OPT is from a Harman Kardon, and it originally matched a pair of EL84s. I measured the voltage ratio while delivering about 3 watts output into 8 ohms. Converted to Z, I calculate 9400 ohms plate-to-plate. Adjusting for resistive loss, I believe it is actually a 9K transformer.

At maximum output, peak grid-1-to-grid-1 voltage swing is approximately 40V, just as noted in the datasheet (and as I would expect based on grid bias). Output power is not the same, though. I measure approximately 14W max into 8 ohms, not the 24.5 claimed by RCA. This seems to agree with the Eico; I'm sure that if I were to increase plate voltage in my circuit to 440V, output would climb to a value closer to 20W. On the other side of the coin, I'm sure that if I used a 6.6K OPT, the circuit would deliver 25-26W.

I wonder if the RCA sheet was intended to say 14.5W, rather than 24.5W. In any event, it certainly appears to be wrong. Let that be a lesson to ya ...

This particular set of values (indicating 24.5W AB1 output with a 9K OPT) does not show up in any of my tube manuals, including a 1961 RCA. It only appears on certain Web sites. Does anyone know which year(s) the RCA manual listed these values?



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