labcoat man
Member
:shock:
HI, wondering if anyone can shed some light on these symptoms
I recently hooked up a discrete Altec Mic pre (quite old!) , and it loves to burn up a particular resistor (22ohm). The voltage around the circuit is quite high in some parts compared to the schematic (but never exceeds 23 volts) its 24volt powered. IN parts where it should read 3.5 volts etc its way up at 23! IM using a regulated 24volt dc PS from the electronics store.
All the resistors and transisitors seem in spec and I changed the electrolytic caps.
The resistor that burns seems to be linked to the negative end of the power supply (which Im assuming is straight dc as opposed to bi polar) but the voltage to the resistors measures quite low (its after a diode). I replaced with a much higher value resistor but still all I get out of the mic amp is a buzzing sound and there seems to be no input signal. ONe thing I haven't done is try a higher watt 22ohm resistor.
Im hoping its not (but thinking it is) a bad output transformer (do these cause wild current in a circuit?) but Im a bit unsure how to test the transformer. Im also wondering whether a functioning full circuit should automatically show continuity between the input and output pins (cause this one dosen't!)
Sorry for the convaluted speil but I have to get it out of my head and in to the realm of someone who knows what they are doing properly!
Id love to have this up and running, Ive heard good things, it is all discrete class A (if that helps) and very big transformers either end so it looks good anyway! I think these were the first solid state altec pre's (or among them) and are similar in construction to langevin AM 16's.
Any tips would be very much appreciated as Im liable to burn myself on the soldering iron the longer I stare at it.
thanks
HI, wondering if anyone can shed some light on these symptoms
I recently hooked up a discrete Altec Mic pre (quite old!) , and it loves to burn up a particular resistor (22ohm). The voltage around the circuit is quite high in some parts compared to the schematic (but never exceeds 23 volts) its 24volt powered. IN parts where it should read 3.5 volts etc its way up at 23! IM using a regulated 24volt dc PS from the electronics store.
All the resistors and transisitors seem in spec and I changed the electrolytic caps.
The resistor that burns seems to be linked to the negative end of the power supply (which Im assuming is straight dc as opposed to bi polar) but the voltage to the resistors measures quite low (its after a diode). I replaced with a much higher value resistor but still all I get out of the mic amp is a buzzing sound and there seems to be no input signal. ONe thing I haven't done is try a higher watt 22ohm resistor.
Im hoping its not (but thinking it is) a bad output transformer (do these cause wild current in a circuit?) but Im a bit unsure how to test the transformer. Im also wondering whether a functioning full circuit should automatically show continuity between the input and output pins (cause this one dosen't!)
Sorry for the convaluted speil but I have to get it out of my head and in to the realm of someone who knows what they are doing properly!
Id love to have this up and running, Ive heard good things, it is all discrete class A (if that helps) and very big transformers either end so it looks good anyway! I think these were the first solid state altec pre's (or among them) and are similar in construction to langevin AM 16's.
Any tips would be very much appreciated as Im liable to burn myself on the soldering iron the longer I stare at it.
thanks