Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Topic started by: xcortes on February 03, 2013, 02:43:42 AM

Title: 300B in Paramour (2.5v filaments)
Post by: xcortes on February 03, 2013, 02:43:42 AM

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

Title: Re: 300B in Paramour (2.5v filaments)
Post by: Paul Joppa on February 03, 2013, 10:11:04 AM

Same as 2A3 - no change.

Title: Re: 300B in Paramour (2.5v filaments)
Post by: xcortes on February 03, 2013, 01:11:46 PM

Cool. Thanks

Title: Re: 300B in Paramour (2.5v filaments)
Post by: RPMac on February 07, 2013, 09:01:05 AM

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

Title: Re: 300B in Paramour (2.5v filaments)
Post by: xcortes on February 07, 2013, 09:33:25 AM

No. A 300B can disipate more power.

Title: Re: 300B in Paramour (2.5v filaments)
Post by: RPMac on February 07, 2013, 10:10:40 AM

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?

Title: Re: 300B in Paramour (2.5v filaments)
Post by: Grainger49 on February 07, 2013, 11:05:32 AM

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?

Title: Re: 300B in Paramour (2.5v filaments)
Post by: Paul Joppa on February 07, 2013, 12:19:42 PM

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).

Title: Re: 300B in Paramour (2.5v filaments)
Post by: Jim R. on February 08, 2013, 05:56:47 AM

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