tube pre amp modeling pspice

[HamiltonPupo]

Hello Hope someone can help with this. I am trying to design my first tube pre amp using pspice. The circuit is attached (sorry for the mess).
My problem is, if i use a VDC source from pspice, everything works beautifully, but if connect my own HV source, as on the circuit attached, i get the voltages on the second image attached. As far as i could understand, it seems the larger the resistance of R6, R11, R12 the longer it will take to the voltage on grid od VL2 to discharge. My first question would be why this happens? Is that due to Miller capacitance? Why it only happens when i use my HV source? Now the most important question, does that happen on a real circuit?

Thanks

[loudthud]

Could it be because C1 is 3uF? Or maybe C5 is 3 Farad? My guess would be that in one case the program assumes the circuit has reached DC stability for initial conditions and in the other case that all caps are discharged and signal sources are off.

[HamiltonPupo]

First of all thanks for the reply. the 3F capacitor was a mistake. It was supposed to be 3uF. I corrected that and changed C1, but i still have the problem. I assume that the DC stability case is for when i use the pspice's vdc source, correct?
Now, i guess the most important question, which one is more accurate? Does this "spike" happens in a real circuit?

[Steve Conner]

No the spike doesn't happen in a real circuit.

The PSpice simulator probably goes unstable when you connect diodes in series. Just forget it and use the VDC: simulating the power supply doesn't really tell you much.

[Wilder Amplification]

Off topic of the original question...that's some pretty heavy duty filtering you've got goin' on there. I wouldn't think you'd need over 100uF total since preamp circuits don't hardly draw any current to speak of.

[HamiltonPupo]

What i was able to investigate, is that this is due to the all the capacitors charging and them discharging. Sort like an inrush current. this got me thinking, is this is due to some sort of in rush current, why wouldn't that happen on a real circuit.
Also, this is my very first design, and i want it to have a lot of bass (i know, maybe i will get too much, but i am willing to experiment). this whole problem started because i was trying to figure out how much current the whole circuit would draw.
Thanks everyone....

[Wilder Amplification]

What i was able to investigate, is that this is due to the all the capacitors charging and them discharging. Sort like an inrush current. this got me thinking, is this is due to some sort of in rush current, why wouldn't that happen on a real circuit.
Also, this is my very first design, and i want it to have a lot of bass (i know, maybe i will get too much, but i am willing to experiment). this whole problem started because i was trying to figure out how much current the whole circuit would draw.
Thanks everyone....

Well if you were trying to accomplish this via big filtering, that will just keep the bass tight, BUT...there does come a point of diminishing returns. And too much filtering can be a bad thing depending on a few factors.

I honestly would use two 47uF filter caps in that circuit...that should be more than enough filtering for what you're doing.

[HamiltonPupo]

Dude, thanks...i really appreciate that. I just realized something, which caps are you referring to? The one after the power supply?

[Wilder Amplification]

Dude, thanks...i really appreciate that. I just realized something, which caps are you referring to? The one after the power supply?

Yes...the filter caps.

[HamiltonPupo]

Actually the 60u was there as a test. I really didnt know what value to use. I will stick with the 47u then....

[HamiltonPupo]

Back to the original subject, am going to see this "inrush" current on a real circuit? Which is more accurate, use pspice's VDC source on my power supply?

[Alex/Tubewonder]

Back to the original subject, am going to see this "inrush" current on a real circuit? Which is more accurate, use pspice's VDC source on my power supply?

Use Pspice native DC vltage source when you want to study circuits behavior when signal is applied, both steady state and transient analysis.

Use a model of your actual supply when you want to look at turn-on transient like the on you're observing now. But use correct models of components. You are not using 1N4148 small signal diodes as rectifiers, are you? They wouldn't survive initial current surge in real circuit. PSpice models of basic components are pretty good and this why you see several kV negative transient, the 1N4148 model collapsed on the turn-on. There should be evidence of this in simulation run log.

[HamiltonPupo]

Thanks Alex...Actually i was. The reason was because i did not know what other one to use. what diode/rectifier bridge do you recommend for the voltages, currents involved in my schematic?

Thanks

[Wilder Amplification]

Thanks Alex...Actually i was. The reason was because i did not know what other one to use. what diode/rectifier bridge do you recommend for the voltages, currents involved in my schematic?

Thanks

A bridge rec circuit with 4 x 1N4007s should be more than enough.

[HamiltonPupo]

Thanks everyone for their inputs. I changed to 1N4007 and still have that transient. One thing that has be noticed, i am getting a transient that goes to KV because this is the amplified signal of the original transient. The actual transient voltage is only about 200V (the voltage after C1). This is actually the reason of my concern. If this transient actually exists on a real circuit, wouldn't it damage the tube?