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In the Forum: Melquiades Amplifier
In the Thread: Single-stage Melquiades vs. DHT amps

Post Subject: 2A3 and 400V supplyPosted by floobydust on: 2/21/2009

Romy,

I did some models using a 400V supply and a 6K OPT load. It's easy to get 4 watts output in this configuration, but using a 2K cathode resistor results in higher distortion and a weak transfer curve. Plate dissipation is around 11 watts and idle current it about 33ma. Dropping the cathode resistor to 1350 ohms improves things quite a bit. Current goes up ~47ma, distortion drops, linearity improves and plate dissipation increases to a little under 16 watts. One area of minor concern is the cathode-to-plate voltage is ~335 volts. While I don't think will be a killer, good quality tubes will be important.

I also did a model using a 45 triode.... seems more viable for a direct replacement. cathode-to-plate voltage is ~328 volts, idle current is ~35ma, power output is 2.8 watts with a plate dissipation of 10.7 watts. This is using the 6K OPT load, 2K cathode resistor and the 400 volt supply. May be worth a try.

As for the 6A3 (or 6B4G), it will function the same as the 2A3 but you will not fare well with AC filaments. I have a dozen pairs and all are configured internally as dual-sections with the a common anode and two separate grids and filaments. The anode is common and the grids are in parallel but the two filaments are wired in series, hence impossible to tame the hum on these. Hope this helps.

Regards, KM

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