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Wanting to Build an EL84 Amp, but which one?

macaltec said:
I have PSUD2 and have figured out how to add and change components. I'm not sure what or where to be looking for the info I need after that. I think I see where B+ is but thats about all I know so far. I have a few books around here on amp building and some tube characteristics manuals. Like I said, I have dabbled a bit in the past. I can only read so much before I need to get hands on. I think Im close.
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Hands on, is the key. Making your own amp is the best experience and teacher. A lot of builders use a "bread board". This has the advantage of allowing easier changes since it is exposed and on a flat surface. But, a large piece of plywood with long test leads everywhere and loose components makes it difficult to move. I rather put my work into a chassis that i can set up in my house and listen to the result on my Altec 19 speakers. this is where following a well known circuit comes in handy. In a fully vetted circuit, sticking with the recipe will yield the expected outcome.
 
Thats cool.

Didnt have much time today to tinker with PSUD2. I have a Hammond amp from a tone cabinet that has the appropriate voltages on the PS and a nice big 15H choke along with a 5U4 rectifier tube. It is tempting use these parts toward the LCLC design. It would certainly save me some money. I cant locate any info on the transformer other than the voltages and no DCR on the choke. I see PSUD2 wants some of those values. Not sure how to proceed....
 
macaltec said:
Thats cool.

Didnt have much time today to tinker with PSUD2. I have a Hammond amp from a tone cabinet that has the appropriate voltages on the PS and a nice big 15H choke along with a 5U4 rectifier tube. It is tempting use these parts toward the LCLC design. It would certainly save me some money. I cant locate any info on the transformer other than the voltages and no DCR on the choke. I see PSUD2 wants some of those values. Not sure how to proceed....
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IIRC, psud wants the dcr of the secondary of the pt and the output.You can measure the secondary voltage by hooking up the primary to your variac at 10% of full voltage. Then measure the AC between the 2 leads of the high voltage secondary x 10 is secondary voltage at wall voltage.
 
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There is potentially a lot of info that needs to be input that I do not have. I do have a schematic for the Hammond amp. In PSUD2 I see the check boxes on the left. I get T1 ,C1, L1 stuff not sure what D1 is or what to set my time as. Then Im back to what to do about information I do not have, is this going to be a math problem using the schematic of the donor amp?
 
You can make educated guesses and be fine with PSUD. Secondary winding is probably between 50 and 100 ohms. Choke DCR for a 15H choke in a Hammond tone cab is prob 300 ohms. Let PSUD default everything else.

The check boxes on PSUD will graph the items checked. V for voltage I for current. Example V(C1) if checked will graph the voltage on the pos terminal of C1 over time.

Simulation time parameters are specified by the "For' box and the "after a reporting delay of" box, and they do exactly as they are described. For = total simulation time in miliseconds. After a reporting delay of = the amount of time after the simulation starts to gather statistics. Graphed voltage or current will show for the time difference between For and After Reporting Delay.

Example:
For = 10,000 mS (10 Seconds)
After Reporting Delay Of = 8 Seconds

The simulation will run for a total of 10 seconds, and data will be gathered for display for the last 2 seconds of the simulation.

It's good to start with simulating steady state conditions of your power supply. The above parameters will give you that. But if you want to investigate the startup characteristics of your power supply, set For to 2 seconds and After Reporting Delay Of to 0 seconds. This will run the sim for 2 seconds and gather data for the first two seconds.
 
Really the only other feature of PSUD I use is the step function on current sources. This changes the amount of current pulled through the current source after the specified time. You can set it to start low and step high or start high and step low. This lets you investigate the dynamic conditions of the power supply.

But (FYI) a choke input power supply stores current reserve in its magnetic field. So a choke input power supply has somewhat constant current regardless of load demand, assuming the size of the choke meets the critical inductance for circuit. (This is why people like choke input supplies). So if modeling a choke input supply, the current source step function may not be that useful.

A capacitor input power supply, on the other hand, stores voltage in its electrical field and tries to keep voltage constant as the load demand changes. But it's easy to deplete the electrical field of a normal size capacitor in a tube amp, so modeling the dynamic behavior of a cap input supply is very useful with the current source step function.
 
The current source thing is really useful for modeling regulation. Single ended amps aren't such a big deal but AB1 push-pull amps have a lot of current swing. You can use datasheet stuff to get an idea of idle current and full load. Put those into the stepped current load and you'll see what it will do under worst case conditions.
 
Yall just went over my head a bit. Its good to know. Im sure as time goes on I will encounter a need for such things. Then I will at least know the right questions to ask.

So, should I be modelling a resistive load or a constant current load. What values?
 
For a SE amp a resistor load is sufficient. Set the resistor size using Ohm's law given the voltage of the power supply and the current draw of both channels. I'm going from memory but I believe the Kegger SE-UL will draw something like 120 to 150 mA. (Both channels).
 
So the T1 is 800V total (400-0-400) divided by .150A equals 5300 or so Ohms. Correct? Looks to me that changing L or C values have little effect on the voltage but resistance values can make it change quickly.
 
I think I lost it. I dont seem to be able to grasp what is up or down. Even using published values from a new transformer leaves me with questions of resistance values. I can fudge the numbers to get the voltage I want but I have no idea how realistic it is. I must be missing something very simple.
 
That looks fine. Resistor should be about 2600 ohms though for a simulated load of 120 mA. That will drop voltage seen at R1 a bit though. Also take a look at ripple by setting "after reporting delay" to 8 seconds.
 
Yes 400 is correct because PSUD wants secondary voltage specified in RMS volts for one leg if using full wave CT rectification. I suspect the designer of PSUD did it this way as to make it easy to switch from full wave to bridge rectification without having to re-specify the power transformer voltage.
 
Ok, I felt like I was stumbling around in the dark second guessing every move I made. So why is D1 so large? Seems alarming to me. What can I do to get the voltage at R1 back up a bit? Im shooting for 330V.
 
I'm going to speak very generally because I'm headed to work:

Your power filter will basically give you 0.9 to 1.4 times the voltage of your power transformer. This is a factor of how much capacitance the first element has versus inductance. 0 capacitance gives 0.9, 40uF and a tube rectifier gives you roughly 1.4 times. If you use a pure "choke input" filter with no capacitance at all, you end up with a power supply described as "current rich and voltage poor". It's a very good supply for a single ended amp, but as you can see you need a lot of voltage to start with, and your first choke has to be substantial because it'll take a hell of a beating.

For this reason, sometimes people design with a "small C" power supply and put like a 1-2uF cap as the first element, to "protect" the choke, and get the voltage up a little. You can also "tune" the filter by altering the first cap value, to get slightly more or less voltage.
 
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