02.08.2014, 10:05 PM
Just like I have already stated, you are mixing the RMS voltage (which increases thanks to the capacitor reducing ripple), and the DC peak voltage which stays the same since the capacitor can only reduce the ripple but cannot change the rectification efficiency.
The BJT thus stay safe if correctly chosen in the first place by the manufacturer, since they are chosen based on peak voltage and current output.
I already stated that this circuit is difficult to understand, and even more difficult to understand the difference made by a cap inserted in the circuit. The main problem is understanding that the perpetuum mobile does not exist and the cap does not change anything besides RMS voltage.
If the current surge happens when you power the circuit, and kills the BJTs, the circuit would not work. But it does, since I have used and am still using it to heat direct heated tubes every day without the slightest problem. I have once had a start-up surge that has blown inadequate power diodes (while modifying a cheap Chinese no name unit), but that was the only damage (no problems with the transistors or anything) and after replacing with more powerful diodes there have been no problems since.
Without the cap modification this circuit is almost irrelevant for audio. A mere toy, cheap solution where you trade 100Hz ripple for 200Hz ripple?! As for safety, it is safe enough for me, works every day and without hum or artefacts, while being efficient - without the cap I would not even considered it.
We have managed to drawn a proposal for superior quality audio application into a discussion about safety where you seem to be giving incorrect arguments. With all due respect, I have better things to do than teach people about RMS, peak values, and duty cycle.
If you do not understand or fear the circuit, just forget about it.
You are not going to build an RH813 anyway, and while to me it is reasonably safe and well engineered, you might and probably should fear the 800+V DC power supply it requires. Is that safe? Well, not if you stick your fingers where they do not belong - but it is safe enough since you have no reason to do that (nothing to measure and adjust in use daily. The same is true of the modified electronic transformer: most do not have the required DMM that is True RMS and capable to measure at least 100kHz.
The BJT thus stay safe if correctly chosen in the first place by the manufacturer, since they are chosen based on peak voltage and current output.
I already stated that this circuit is difficult to understand, and even more difficult to understand the difference made by a cap inserted in the circuit. The main problem is understanding that the perpetuum mobile does not exist and the cap does not change anything besides RMS voltage.
If the current surge happens when you power the circuit, and kills the BJTs, the circuit would not work. But it does, since I have used and am still using it to heat direct heated tubes every day without the slightest problem. I have once had a start-up surge that has blown inadequate power diodes (while modifying a cheap Chinese no name unit), but that was the only damage (no problems with the transistors or anything) and after replacing with more powerful diodes there have been no problems since.
Without the cap modification this circuit is almost irrelevant for audio. A mere toy, cheap solution where you trade 100Hz ripple for 200Hz ripple?! As for safety, it is safe enough for me, works every day and without hum or artefacts, while being efficient - without the cap I would not even considered it.
We have managed to drawn a proposal for superior quality audio application into a discussion about safety where you seem to be giving incorrect arguments. With all due respect, I have better things to do than teach people about RMS, peak values, and duty cycle.
If you do not understand or fear the circuit, just forget about it.
You are not going to build an RH813 anyway, and while to me it is reasonably safe and well engineered, you might and probably should fear the 800+V DC power supply it requires. Is that safe? Well, not if you stick your fingers where they do not belong - but it is safe enough since you have no reason to do that (nothing to measure and adjust in use daily. The same is true of the modified electronic transformer: most do not have the required DMM that is True RMS and capable to measure at least 100kHz.