Great tool but I need a little info!

[tubedood]

Hi guys... A little help on this site if you could... http://thesubjectmatter.com/calcptcurrent.html

it calculates our current draw to help in choosing a power transformer. Cool Beans!

But I am a little confused when it comes to an entry where we can provide RLoad in a Push Pull circuit Is this merely my primary tranny value? It tends to really make the recommended ma go all over the place if I change it.
Hope all is well my friends and talk soon.

[Chuck H]

regarding the figure you're wondering about, the instructions say: Optional Rload in Ohms (typically the output transformer primary impedance)

So yes. The OT primary impedance would be the load. The mA changes because the calculator assumes the tubes are conducting signal, not at idle. So if you raise or lower the load the operating conditions change. But I was also surprised at how much the load changed the operating current. I don't know if it's that variable in the real world either.

[g1]

A good example of how impedance mismatch to load will impact tube life.

[tubedood]

I was trying to use it to see if my lil 100ma power transformer could handle a load of 2 12AX7's and a 6L6GC in a single ended amp . According to it I'll be in at about 104ma.

A little hi unless you folks say it will work!

[nickb]

regarding the figure you're wondering about, the instructions say: Optional Rload in Ohms (typically the output transformer primary impedance)

So yes. The OT primary impedance would be the load. The mA changes because the calculator assumes the tubes are conducting signal, not at idle. So if you raise or lower the load the operating conditions change. But I was also surprised at how much the load changed the operating current. I don't know if it's that variable in the real world either.

The calculation has some simplifications (don't they all?). For one, it assumes that the tubes are more like voltage sources than current sources. So, if you enter a low load impedance, you will get absurdly high currents that can never happen in practice. If you stick to reasonable numbers you will get reasonable results.

It's a pity that a diode bridge is not included in the list rectifier choices as it is the most efficient one but you if you multiply the result for full wave by 1.4 you'll be close. It also does not take into account the fact the you won't be using it at full output 100% of the time. Music is dynamic so the average power out is much lower. Therefore, the currents the calculator come up with are conservative. Nothing wrong with that, but it's worth knowing. Just look at the wimpy PT's on many production models hat assume very low average output power.

[mozz]

Data sheet for se shows 66ma at 350v plate 4.2k load.

[tubedood]

Thanks everyone! This site is awesome. I appreciate everyone's help.