Simple premise, zeners facing into each other across the primary of an OPT that will clamp the voltage in the case of accidental load disconnection or amp misbehaviour to something slightly above the maximum anode swing of the amplifier is capable of. Zeners would probably consist of X amount of 200V zeners to make up various ballpark values, 400v, 600v etc
Is this worth doing? I don't think I've seen it implemented before. It sounds like a worthwhile addition to amplifiers considering high voltage 5W zeners are so cheap
Is this worth doing? I don't think I've seen it implemented before. It sounds like a worthwhile addition to amplifiers considering high voltage 5W zeners are so cheap
You may use some modern MOSFET with gate and source connected together. They work as Zeners on high voltages, and most of them have a diode that shunts an opposite polarity. However, if you connect gate to cathode of your output tube through an appropriate thermo regulated voltage divider you can get a "tube on steroids", like I do in my Barracuda amp.
I've read of it as a safeguard in pentodw amps, which are the ones normally associated with OPT primary overvoltage if the load is accidentally disconnected. I can't remember where I saw it though. A simpler safeguard would be to connect a resistor of about 1k permanently across the secondary, so it can never be completely unloaded.
There are some issues - primarily oscillations and RF emissions associated with those kinds of circuits. I suggest looking at some texts related to switchmode power supply design as the same issues are present there. On the primary side of the power transformer of a switchmode supply, you typically find all sorts of voltage limiters, snubbers, etc.
Whether adding such a circuit will prevent amp meltdown if the load is disconnected is another story. But it will limit the primary voltage...
~ Tom
Whether adding such a circuit will prevent amp meltdown if the load is disconnected is another story. But it will limit the primary voltage...
~ Tom
bigwill said:
What is the capacitance of a non-conducting 5W zener? With the zener there you'd have a shunt to ground for some higher frequencies. But likely well above the audio range.
What about placing a fuse in series with the Zener? Then if it ever does conduct the fuse will blow quickly. Then you feed the B+ supply to the xformer through the fuse. When the Zener conducts the fuse blows and disconnects B+ supply and the amp shuts down. Or at least the OPT is no longer powered.
To answer the question about the gas discharge unit. They are very easy to find. They are used in communications antenna to shunt a lightening hit to ground. You can buy them from any place that sell radio gear for a few bucks each. But. I think they need some huge number of amps to trigger. They work when a spark jumps the gap and ionizes the gas which makes the gap more conductive. But they are made to handle 1000+ amps as in a direct lightening strike
Look here for more details
http://www.alphadeltacom.com/pdf/Transi-Trap installation and tech data.pdf
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.