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In the Forum: Melquiades Amplifier
In the Thread: Single-stage Melquiades vs. DHT amps
Post Subject: Some interestng modelsPosted by floobydust on: 5/23/2009
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One of the reasons I no longer use a tube tester. They make a measurement at a specific target operating point(s). You don't really know what it is, so what are the chances they will be close to your actual circuit operating point? So choosing a close match of tubes that perform the same across the noted parameters (in the actual amplifier(s)) just makes more sense to me. If the pair of tubes are the same manufacturer and internal construction (and unused), then they should age well together and remain fairly matched in long-term operation.
Just for fun, I took the final output stage for the DHT amp and normalized it (i.e., subtracted the DC shift for direct-coupling) and modeled it in the SEampCAD program. I plugged in the details for the output iron as noted. Normalized values result in 1.125K cathode resistor and a 280V plate supply. Values work out to pretty much what you show in measured values.
Transfer curve is quite good considering the lower current. Maxmum power output is about 1.85 watts with pretty low distortion. I can probably create some PDFs for the output specs and curves and email them to you.
Based on the values you are currently using, you can put a 45 triode in the circuit without any change and it will be just as clean but less power... about 1.2 watts. Should be an interesting experience. In many respects the 45 is the purer tube design and many prefer it soncically over the 2A3, "IF" you can deal with 2-3dB less output power.
Regards, KMRerurn to Romy the Cat's Site