PSUD newbie: modeling Tubelab SE

[PaulyT]

Hi! I'm just starting to play with PSUD (II), and would like to model the Tubelab SE that I'm building. Has anyone done a model for this amp?

I'm not quite sure how to translate the TSE schematic into the components available in PSUD. I am using a choke in place of R4. Do I need to include R30 somehow? What is a reasonable value for a resistive or current load? I'm not sure how to estimate that.

Attached is what I've got so far. The sim stabilizes at about 410V, so I'm sure I'm not doing it right... any suggestions?

[boywonder]

Looks good to me. R30 is just a bleed resistor for the caps so when you power down the amp, you don't get zapped; you don't need to include it in the model, as it's drawing a mouse-fart's worth of current.

Your current load looks good, it should be the sum of the currents of all of the tubes. Most of the current is for the output tubes, the input tubes draw a little. Tubelab George has a page for Voltage and current recommendations for different tubes, so the total current load will depend on if you are using 45's, 2A3's, 300b's etc. the page is here:

http://www.tubelab.com/AssemblyManua...ormers_TSE.htm

Two things that you can tweak:

Adjust the value of C1 to change the B+ voltage. Lower C1 lower voltage, higher C1, higher voltage.

You can also use the "stepped load" function in the current load box. Set it for "stepped load" and change the current say 20 ma or so up or down after 4 seconds or so. You want the step to occur after the B+ voltage settles out.

Check for ringing (oscillations) of the voltage when you step the load. You should have no ringing, ie an overdamped system. You can also adjust the cap values to attenuate ringing.

Zoom in on the flat part or the B+ waveform to see how much AC ripple remains on the DC voltage. Adjust C's and R's to minimize this.

Adding R/C sections or R/L sections greatly reduces ripple but drops volts and increases the PS output impedance.

You can also try different L's: I use Hammond's data sheet to estimate the R for a given L.

[boywonder]

I just duplicated your model. It appears that you have a some overshoot/ringing on startup, and you B+ is a little high (assuming 300B's). If you are planning on running 45's, it's alot high.

The stepped response looks fine.

Reducing C1 to 10u or less reduces the startup overshoot and gets you away from the ragged edge of exceeding the max forward current of the 5AR4. If you see the "forward current has been exceeded" message, the current rating of the rectifier is being exceeded, and the rectifier tube can arc over under these conditions. The current is high at startup, since the caps are discharged and have low resistance until they get charged up.

Dropping the value of C1 below 10u or so also starts to reduce the B+ voltage, so that's how you adjust B+. Assuming 300B's, try a C1 of 10u and a stepped load of 120ma stepped to 140ma after 4 seconds.

For additional fine tuning, measure the resistance of the transformer secondary, and input that R value in the transformer box.

[Sheldon]

Your power transformer spec's look suspiciously like the stock sample for the software. Make sure you use values that reflect the actual part you will be using. Someone here will have measured the unit. You need the unloaded output voltage, and resistance of the primary and secondary. Edit the transformer values, by clicking on the Ohms button in the transformer edit box.

Sheldon

[luvdunhill]

For additional fine tuning, measure the resistance of the transformer secondary, and input that R value in the transformer box. [/B]

If you have a center tapped winding, do you measure this resistance from the center tap, or across the entire winding?

[Sheldon]

Originally posted by luvdunhill
If you have a center tapped winding, do you measure this resistance from the center tap, or across the entire winding?

For a CT full wave, only one half of the secondary is conducting at any given time, so both voltage and resistance should be measured from the CT to either end.


Sheldon

[luvdunhill]

Ok, I measured things. Perhaps someone can check my numbers as well It's a RCLC supply

T1 is 365V, 241 ohms (unloaded, actual unloaded voltage). Center tapped

D1 is 1N4007x2 full-wave SS

R1 is 4.7 ohm (not sure if this is needed, but series resistor)

C1 is 100uF cap

L1 is 40H, 603.488 DCR (actually measured)

C2 is 100uF || 47uF caps

load is 40mA. I'd like to get 450V, but I'm not thinking that is possible Somewhere around here is fine.

[boywonder]

Originally posted by luvdunhill
Ok, I measured things. Perhaps someone can check my numbers as well It's a RCLC supply

T1 is 365V, 241 ohms (unloaded, actual unloaded voltage). Center tapped

D1 is 1N4007x2 full-wave SS

R1 is 4.7 ohm (not sure if this is needed, but series resistor)

C1 is 100uF cap

L1 is 40H, 603.488 DCR (actually measured)

C2 is 100uF || 47uF caps

load is 40mA. I'd like to get 450V, but I'm not thinking that is possible Somewhere around here is fine.

I just modeled it (I'm at my desk on my lunch break ) and I got a B+ of 440V. I usually use the loaded/rated voltage of the transformer in PSUD, so using the unloaded transformer voltage is new to me, but I'm no expert.

Everything looked fine except that the forward voltage of the 1N4007's was exceeded (1002 volts, PIV for 1N4007 is 1000V)

What the rated voltage of the transformer? (Assuming the transformer is rated for around 40 ma)

[Sheldon]

Originally posted by luvdunhill
Ok, I measured things. Perhaps someone can check my numbers as well It's a RCLC supply

T1 is 365V, 241 ohms (unloaded, actual unloaded voltage). Center tapped

D1 is 1N4007x2 full-wave SS

R1 is 4.7 ohm (not sure if this is needed, but series resistor)

C1 is 100uF cap

L1 is 40H, 603.488 DCR (actually measured)

C2 is 100uF || 47uF caps

load is 40mA. I'd like to get 450V, but I'm not thinking that is possible Somewhere around here is fine.

Is the transformer figure for the secondary, or the calculated value for the source resistance?

With those figures, I get about 360V. If it's the source resistance, that added to the inductor resistance is about 850R. At 40mA, you are dropping a good bit of voltage.

Sheldon

[luvdunhill]

Originally posted by boywonder



I just modeled it (I'm at my desk on my lunch break ) and I got a B+ of 440V. I usually use the loaded/rated voltage of the transformer in PSUD, so using the unloaded transformer voltage is new to me, but I'm no expert.

Everything looked fine except that the forward voltage of the 1N4007's was exceeded (1002 volts, PIV for 1N4007 is 1000V)

What the rated voltage of the transformer? (Assuming the transformer is rated for around 40 ma)

I meant to say that I used the "1N4007x2" option or whatever it is, to help with the PIV

well, the help button says to use the unloaded voltage, so that's what I did The transformer is rated at 300-0-300 @ 95mA, so it will be unloaded somewhat.