Hi Thomas, nice little oscillators, I had an automotive multimeter from Escort and it was great. I recently made an audio attenuator with the possibility of inserting a RIAA curve so that I could test the turntable inputs with a line signal. The source was made using 7809 and 7909, because I didn't have any 7909 at home anymore, I bought 5 new ones and I couldn't stop wondering what kind of interfering signal was coming out of them - I gradually tested all of them and some were completely unusable - probably a Chinese fake. I first saw the diode divider for converting a sawtooth signal to a sine at HP and it worked perfectly luxuriously there, I have no idea if they even invented it at HP. Just a thought without looking at the wiring diagram - wasn't the negative source designed to interact with the positive and thus ensure greater stability, using 78 and 79 each branch works separately and could result in uneven powering of the + and - circuit. Nice day 🙂 Tom
Almost certainly the idea about regulating the -15V with a transistor (rather than a’7915) has been to match the negative and positive voltage values. The is also likely an op-amp and a couple of 1% or better matching resistors. And then something (a capacitor) to stabilize the inverting regulator. In that situation, if the amplifier is faster than the transistor, or if there is no resistor from the amplifier output to the transistor base, I have seen parasitic oscillations develop. In my first case, decades ago, I recall something between 2 and 5 MHz. Your ‘7915 solution is likely to make a few more millivolts difference in the positive and negative rail values. That will probably affect the linearity at the very low end of each range.
I had the idea too, but the voltage to the analog stages is only a matter of how soon you hit clip, they could be 500mV apart and no one would see it, the DC ofset is far from calibrated to perfect zero, just a dial until happy kind of approch all over, all i see is a zener a few caps and resistors, not opamps nice stuff to handle this, just too bad i can not find a schematic, by the way i fixed 5 of them this week, not just the 3 as shown in the video :-)
I am so sorry I was wrong : Thanks Jack for the schematics, you need to search for KENWOOD FG-272 servicemanual, that pdf has the schematic in the end, you are right : the PNP is infact controlled by U8 opamp a voltage pos to neg side mirror, but there is a capacitor missing pin 2-6 on that opamp, this will make the voltage stable, no frequency compensation or bw control, however the positive rail is made of 7815 and a gnd pin diode = 15.6 and now it is temperature dependent due to the diode, so clearly they dont care much about the voltage stability
Oh that wiring, design is not a patch on the Phillips equipment. Seems to work quite well though. A few years back I was looking for a good frequency counter and got given a tip by a surplus dealer, they reckoned the exterior appearance of the equipment was a good indicator that it had been in regular use and was more likely to be working than the clean and new looking gear. For his stock, it certainly seemed to be true, the scuffed, dirty, covered in stickers (cal stickers usually, always check the dates) tended to be complete and usually wkring, the brand new looking stuff was often missing bits, blown up or faulty in some other way.
I find it interesting, amusing, and a bit sad that equipment likely used in business engineering settings is not maintained. Someone was using that poor generator till everything got loose and wonky.
Hi Thomas, nice little oscillators, I had an automotive multimeter from Escort and it was great. I recently made an audio attenuator with the possibility of inserting a RIAA curve so that I could test the turntable inputs with a line signal. The source was made using 7809 and 7909, because I didn't have any 7909 at home anymore, I bought 5 new ones and I couldn't stop wondering what kind of interfering signal was coming out of them - I gradually tested all of them and some were completely unusable - probably a Chinese fake.
I first saw the diode divider for converting a sawtooth signal to a sine at HP and it worked perfectly luxuriously there, I have no idea if they even invented it at HP.
Just a thought without looking at the wiring diagram - wasn't the negative source designed to interact with the positive and thus ensure greater stability, using 78 and 79 each branch works separately and could result in uneven powering of the + and - circuit.
Nice day 🙂 Tom
Almost certainly the idea about regulating the -15V with a transistor (rather than a’7915) has been to match the negative and positive voltage values. The is also likely an op-amp and a couple of 1% or better matching resistors. And then something (a capacitor) to stabilize the inverting regulator. In that situation, if the amplifier is faster than the transistor, or if there is no resistor from the amplifier output to the transistor base, I have seen parasitic oscillations develop. In my first case, decades ago, I recall something between 2 and 5 MHz. Your ‘7915 solution is likely to make a few more millivolts difference in the positive and negative rail values. That will probably affect the linearity at the very low end of each range.
I had the idea too, but the voltage to the analog stages is only a matter of how soon you hit clip, they could be 500mV apart and no one would see it, the DC ofset is far from calibrated to perfect zero, just a dial until happy kind of approch all over, all i see is a zener a few caps and resistors, not opamps nice stuff to handle this, just too bad i can not find a schematic, by the way i fixed 5 of them this week, not just the 3 as shown in the video :-)
I am so sorry I was wrong : Thanks Jack for the schematics, you need to search for KENWOOD FG-272 servicemanual, that pdf has the schematic in the end, you are right : the PNP is infact controlled by U8 opamp a voltage pos to neg side mirror, but there is a capacitor missing pin 2-6 on that opamp, this will make the voltage stable, no frequency compensation or bw control, however the positive rail is made of 7815 and a gnd pin diode = 15.6 and now it is temperature dependent due to the diode, so clearly they dont care much about the voltage stability
@@TeardownOZ2CPUMaybe they just had a big stock of those transistors and wanted to use them up :)
need one of this..❤ Great!
Oh that wiring, design is not a patch on the Phillips equipment.
Seems to work quite well though.
A few years back I was looking for a good frequency counter and got given a tip by a surplus dealer, they reckoned the exterior appearance of the equipment was a good indicator that it had been in regular use and was more likely to be working than the clean and new looking gear.
For his stock, it certainly seemed to be true, the scuffed, dirty, covered in stickers (cal stickers usually, always check the dates) tended to be complete and usually wkring, the brand new looking stuff was often missing bits, blown up or faulty in some other way.
old generrator is special
I find it interesting, amusing, and a bit sad that equipment likely used in business engineering settings is not maintained. Someone was using that poor generator till everything got loose and wonky.