300B in Paramour (2.5v filaments)

[xcortes]

I have a pair on loan from keto that I'd like to try in a pair of Paramours. What would be a good operating point/cathode resistor?

Thanks

[Paul Joppa]

Same as 2A3 - no change.

[xcortes]

Cool. Thanks

[RPMac]

So, a 300b and 2a3 are essentially the same except for filament voltage?

[xcortes]

No. A 300B can disipate more power.

[RPMac]

Right, Xavier, let me modify my question.


So, a 300b and 2a3 are essentially the same except for filament voltage if run at same operating points?

[Grainger49]

Let me throw a monkey wrench in the machine here.  Isn't the JJ 2A3-40 a tube with 300B internal structures but with a 2.5V heater so it can run as a 2A3 rather than a 300B?

[Paul Joppa]

Both tubes have very similar parameters - mu (3.85 vs. 4.2), transconductance (5500 vs. 5250 micromhos), and plate resistance (700 vs. 800 ohms). They also have filaments that need nearly the same power (2.5v at 2.5A, vs. 5v at 1.2A). But the 300B has higher ratings for plate voltage (450v vs. 300v), cathode current (100mA vs. 60mA), and plate dissipation (40 watts vs. 15 watts).

[Jim R.]

And in the paramour, you're limited by the available power of the power transformer, so you're not going to get any more power out of it.  Just possibly a slightly different presentation, and probably longer tube life.

-- Jim