MagneQuest/Peerless Forum Welcome! Need support, you got it. Or share your ideas and experiences.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ MagneQuest/Peerless Forum ]

---

[ Alert Moderator ]

---

First Simulation

Posted by jdrouin (A) on March 11, 2017 at 14:42:36

In Reply to: TFA-204 300B Operating Points posted by jdrouin on March 7, 2017 at 12:34:03:

After doing some more digging, I found a thread here where Mike indicated the DC series resistance of the TFA-204 primary is 140 ohm.

Also, the previous LTSpice schematic contained an error. I though I had to enter the 5VDC voltage source for the 300B filament, but that is assumed by the software. Instead, you treat that as a cathode. So I removed the 5VDC source and added the cathode resistor with bypass capacitor that I had mistakenly left off before.

A member of diyaudio (where I'm also modeling a Fi Primer 300B with the TFA-204) helped me figure out that, since the primary inductance is 10H, and the turns ratio is 18.26, the inductance for the secondary should be 0.03H in the sim: 10/18.26^2 ~ 0.03H.

With all of that information entered into the model, and with a hypothetical rectified B+ of 358V after the PS (not modeled yet) and a cathode resistor value of 1.2K, we get 350V on the plate and current that peaks to about -61V. The sine wave of current through the TFA-204 primary goes from about -41mA to -61mA peak-to-peak, which seems close to the 8W option originally posted (350V, 60mA, -74V, into 3K = 8w output).

Does that seem right?

Does the 300B datasheet rating mean -60mA RMS or peak?

I don't know what the grid voltage is right now, and I still have to model the power supply.

Also, if this really results in 8W output, it's pushing up against the maximum of the TFA-204 power rating. Wondering if I should aim for the 300V, -50mA, 6W option.

Edits: 03/11/17 03/11/17 03/11/17 03/11/17 03/11/17

This post is made possible by the generous support of people like you and our sponsors:

Amplified Parts

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---