Hello.
I am using PSPICE to simulate the output stage of a tube amplifier. I am using a 420v DC and an output transformer.
The voltage on the plate of the tube swings between 840v and 420v. I know that the output transformer opposses the current change, but I thought that the voltage should swing up and below the 420v, not between 840v and 420v.
Is it operating correctly? I mean can the voltage swing between VDC Max and higher?
It's probably a simulator anomaly. Run more cycles of the simulation to allow the inductor (transformer) to reach current equilibrium.
And post your schematic, in case you have mis-wired.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
No.
Something's certainly amiss. Check your DC conditions first.
Graham
Is this a push-pull stage or single-ended? If push-pull, then one plate should go up as the other goes down, and the average of the two plates should be close to 420 V.
If the tube models are crappy, then they may be modeled as self-powered current sources, and all sorts of insane anomalies are possible unless the models are used in exactly the operating mode they were designed for. Since SPICE doesn't have intrinsic tube models, I've seen all sorts of derived models, some pretty good, and some just optimized to fit curve tracer charts in one specific case.
Yes, specifically, the voltage at the plate certainly can go above the plate supply. Any time the plate current is decreasing, then the voltage HAS to go up. But. for the plate voltage to ALWAYS be above the DC supply tells me SOMETHING has to be wrong. Assuming the transformer model includes winding resistance, which is usually substantial in these transformers, then even the steady state voltage should be less than 420 V, and the average over an AC cycle should be just below 420 V. I'd take a close look at the tube model. It sounds like it might be one of those current-source type models, and is driving current the WRONG way, too!
Jon
In message , dated Fri, 15 Sep 2006, Jon Elson writes
Excellent; we've always wanted complementary tubes! What do they use to emit the positrons?
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
Cross coupled black holes seem to work quite well
martin
To a first approximation, the average voltage across a transformer winding must be zero. So I agree that the plate voltage for a transformer winding whose other end is tied to 420 volts, should swing above and below 420 volts.
"Lost'n Found" wrote in news:DMOdnZKL59doaJfYnZ2dnUVZ snipped-for-privacy@comcast.com:
If you've modeled the transformer with coupled inductors (K directive) the results may not end up acting the way you want 'em to. I use the sub circuit below for simple OT modeling.
P1 and P2 are the two ends of the primary with Pc the primary center tap. OUT is the secondary (the other end of the secondary is grounded internally in the subckt). The parameters Zp and Zs are primary and secondary impedance respectively. Hope it helps.
.SUBCKT OTRX P1 Pc P2 OUT
+PARAMS: Zp=5000 Zs=16 R1 N002 P2 1 G1 Pc N004 N002 Pc 1 G2 0 N004 OUT 0 {sqrt(Zp)/sqrt(Zs)} G3 N002 Pc N004 0 1 G4 OUT 0 N004 0 {sqrt(Zp)/sqrt(Zs)} R2 N004 0 1G R3 OUT 0 {Zs} R4 N001 P1 1 G5 Pc N003 N001 Pc 1 G6 0 N003 0 OUT {sqrt(Zp)/sqrt(Zs)} G7 N001 Pc N003 0 1 G8 0 OUT N003 0 {sqrt(Zp)/sqrt(Zs)} R5 N003 0 1G .ENDSElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.