The mA of what? Please define "Tx" and the context of your question. It would then be easier to answer your question. There are many different definitions for the generic "Tx".
Sorry I thought it was a simple question. Newbie mistake!
I'm working on a SE 6BQ5 amp that I hope will put out about 5 watts. The idle current, power stage plates+screens + gain stage plates is about 100mA.
The peak will be about 200mA.
I have two Power Transformers to choose from. 275-0-275, 150mA and 275-0-275, 200 mA.
When selecting the power transformer do you use the idle load of 100mA or the peak load of 200mA?
A short comment on why would be appericated.
I'm working on a SE 6BQ5 amp that I hope will put out about 5 watts. The idle current, power stage plates+screens + gain stage plates is about 100mA.
The peak will be about 200mA.
I have two Power Transformers to choose from. 275-0-275, 150mA and 275-0-275, 200 mA.
When selecting the power transformer do you use the idle load of 100mA or the peak load of 200mA?
A short comment on why would be appericated.
Your plate voltage is going to be around 300v. That means you need to keep your plate current to 40ma. to stay under the 12W PD. Total I about 45ma. I have a Magnavox SE 6BQ5 that uses a 140ma PT. It gets pretty warm but not worrisome hot. Those ratings are RMS so you don't need to calculate peaks. Not sure how you got 200ma from 100ma.
The 150ma tranny will be all you need. No reason for overkill unless you want to spend more, have a heavier amp and a larger chassis. Keep in mind you don't want to crowd the all trannies together. You need an adequate margin of space to eliminate magnetic coupling and hum.
55 watts in, 5 watts out. Sounds about right for valves.
You didn't say, but this is mono?
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Thanks everybody for your patience and replies.
I think I got off on the wrong foot by trying to keep my original question brief so let's try this again.
I'm working on a two channel SE 6BQ5 amp that I hope will put out about 5 watts. The idle current power stage plates+screens + gain stage plates is about 100mA (which most of know by heart).
I'm struggling with a little confusion about current requirements. From what I have read and from studying load lines it seems clear that when you increase the grid voltage the current goes up. I assumed this increase would come from the power transformer. Then to further my confusion I read in "Valve Amplifiers" from the chapter Choosing Caps and Transformers that for class A amps "the quiescent current equals the peak current required at maximum power output". The conclusion is, I missed something along the way.
To short cut my problem, for now, I ask you.
I have a 150mA and a 200mA 275-0-275 transformer, which should I use?
The answer would be helpful. Why would be very helpful.
In addition, a tip on entry level reading about power transformers would be appreciated. The tube books I have are short on explaining Power Tx's.
I think I got off on the wrong foot by trying to keep my original question brief so let's try this again.
I'm working on a two channel SE 6BQ5 amp that I hope will put out about 5 watts. The idle current power stage plates+screens + gain stage plates is about 100mA (which most of know by heart).
I'm struggling with a little confusion about current requirements. From what I have read and from studying load lines it seems clear that when you increase the grid voltage the current goes up. I assumed this increase would come from the power transformer. Then to further my confusion I read in "Valve Amplifiers" from the chapter Choosing Caps and Transformers that for class A amps "the quiescent current equals the peak current required at maximum power output". The conclusion is, I missed something along the way.
To short cut my problem, for now, I ask you.
I have a 150mA and a 200mA 275-0-275 transformer, which should I use?
The answer would be helpful. Why would be very helpful.
In addition, a tip on entry level reading about power transformers would be appreciated. The tube books I have are short on explaining Power Tx's.
The power supply filtering keeps the current demanded of the PT relatively constant, +/- the ripple. The PS puts out DC+ripple. In your SE amp you use a high quiescent current set near the point of max plate PD. Or, in your case, you want 5W output signal power per channel, which would be about 10w PD instead of the max 12W PD for a 6BQ5. The drive signal level creates an average current change of 0 since it fluctuates plus and minus the grid bias voltage. This is all the engineers care about since it is what generates the heat. So the definition you cite is correct that SE class A amp quiescent current is the peak current for the max power. You have to figure out where to set the current based on your plate/screen voltage. So your amp won't need more than a 150ma tranny.
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