if it did, your preamp wouldn't have been blown and all the other circuits should not have blown. i dare think what would have happened if you had touched the chassis at the time.
That is exactly their purpose, but they have ratings in terms of energy at turn on and current draw etc.
It's not a good idea to turn on the amp, turn it off then immediately turn it back on again when they are already hot. You will blow fuses and stress the part. Always give it a minute or so before turning it back on again.
makes sense, I guess it's job is to choke an inrush and not be sacrificed, letting excess current thru to the rest of the components
It has both a higher turn on resistance (20 Ohms vs 10 Ohms) ie softer start and can absorb way more energy (4 times as much from memory)
thanks, looks like worth replacing the two cl60's on my mains block from the AC input to the transformer with these then
There are two locations where the thermistors are typically used. The main use is for a soft-start feature on the primary side of the power transformer. The type of thermistor used in this location may depend on whether there are dual primaries or a single one. Many of the power transformers we use these days have dual primaries to support different AC mains voltage. In the case where the AC mains are at 120 VAC, the primaries are wired in parallel, and a thermistor is placed in series each primary winding. This arrangement shares the initial start-up energy between two devices. I tend to prefer the CL-70 for this application, due to its higher initial resistance of 16 Ohms. It has the same maximum energy rating as the CL-60, but a lower current range which is suitable for the FW clone amps that we typically build. The MS22-20005 mentioned by 2 picoD is also an excellent part to use for this application, and is preferred for transformers with a single primary winding, or in cases where two primaries are wired in series to support 240 VAC mains.
The other place where thermistors are sometimes used is to connect audio ground to the chassis. This is a ground lift application that must also support momentary high current during electrical fault conditions. The ground lift path must be able to conduct current until the AC inlet fuse blows, or the AC branch circuit breaker is tripped. While CL-60 thermistors are frequently used in this application, they are perhaps not the best. It was this use of the CL-60 which failed during the power fault described here.
For the audio ground lift, I prefer a 35 Amp block rectifier wired to present a pair of diodes in anti-parallel between the audio ground and the chassis. I also place a 10 Ohm, 2 Watt resistor across the diodes, which sets the normal (non-fault) ground lift resistance. In the case of a power fault, the rectifier will impose a diode drop of about 0.9 to 1.1 Volts while conducting the fault current between audio ground and the chassis. This should suffice to trip the local line fuse or the AC circuit breaker on the branch circuit, whichever comes first.
The other place where thermistors are sometimes used is to connect audio ground to the chassis. This is a ground lift application that must also support momentary high current during electrical fault conditions. The ground lift path must be able to conduct current until the AC inlet fuse blows, or the AC branch circuit breaker is tripped. While CL-60 thermistors are frequently used in this application, they are perhaps not the best. It was this use of the CL-60 which failed during the power fault described here.
For the audio ground lift, I prefer a 35 Amp block rectifier wired to present a pair of diodes in anti-parallel between the audio ground and the chassis. I also place a 10 Ohm, 2 Watt resistor across the diodes, which sets the normal (non-fault) ground lift resistance. In the case of a power fault, the rectifier will impose a diode drop of about 0.9 to 1.1 Volts while conducting the fault current between audio ground and the chassis. This should suffice to trip the local line fuse or the AC circuit breaker on the branch circuit, whichever comes first.
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great explanation, thank you. What's the best guess for the failure of the CL60 acting as the ground lift? What conditions could have caused it to fail and allow the current to fry the boards?
Wayne also produced a nice ground lift circuit that allows a connection to earth under fault conditions.
Did you actually say which thermistor exploded?
I was under the impression it was the ICL thermistor connected to mains and not the chassis earth thermistor.
Did you actually say which thermistor exploded?
I was under the impression it was the ICL thermistor connected to mains and not the chassis earth thermistor.
Check all soldered joints and all connections.
Check psu rails aren't shorted to the chassis via the stand offs. The standoffs are in very close proximity to the rail output. I have managed to experience this condition in the past.
Check psu rails aren't shorted to the chassis via the stand offs. The standoffs are in very close proximity to the rail output. I have managed to experience this condition in the past.
Thanks - I used my own standoffs that were bigger. Everything under the PSU looks OK - nothing burned there.
Are the Jensen transformers likely to be OK? How would I test?
When I pushed the plug into this aged and loose receptacle, there was an arc at the plug and then that really bad smell. Amp and Pre both damaged. Surge protector fuse open
Not clear about what plug was 'loose' from this - was it the mains power plug? If so, perhaps your earth wire touched the active wire in the faulty mains plug/socket - that would produce something like this result
Not clear about what plug was 'loose' from this - was it the mains power plug? If so, perhaps your earth wire touched the active wire in the faulty mains plug/socket - that would produce something like this result
Not clear about what plug was 'loose' from this - was it the mains power plug? If so, perhaps your earth wire touched the active wire in the faulty mains plug/socket - that would produce something like this result[/QUOTE]
It seems that the plug of the surge protector in the wall receptacle created a short at the (likely damaged) receptacle. In other words, the short happened outside the amp I believe.
I'm trying to assess the damage at this point.
It seems that the plug of the surge protector in the wall receptacle created a short at the (likely damaged) receptacle. In other words, the short happened outside the amp I believe.
I'm trying to assess the damage at this point.
The washers can make contact with your psu rail then go through the stand off to chassis.
There should be no issues with your Jensen transformers unless you had mains voltage go through your rca interconnects, and even then most likely jfets would fail first and protect the transformers.
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