No I haven't drawn the 725C analogue input stage. If no one is interested in the ShibaSoku I might get around to it. I believe that it is only single ended though. A fair bit of the magic is going to be in the layout.
I fully intend to do the same for mine. I'll try to get started this weekend. I suspect the circuit will be very similar to the oscillator.
PChi can you determine the number of sample per cycle the 725 uses? I would like to know what the minimum number required to capture the 5 harmonics is.
Rick I have a friend who has a son living in Tokyo. I might be able get her to ask Frank if he can have a look around for the manual. Give me the model revision number you're after.
He might say no but it's worth a try.
He might say no but it's worth a try.
It is a model AD725D, S/N is M-61518002
The rep in USA is not able to get us any manuals. Tektronix bought out a repair depot in California and they will calibrate the analyzer (repair as well, I presume?). Of course, they wont give out manual or copies or schematics, either.
Governments should be so lucky with keeping thier secrets.
Thx-RM
The rep in USA is not able to get us any manuals. Tektronix bought out a repair depot in California and they will calibrate the analyzer (repair as well, I presume?). Of course, they wont give out manual or copies or schematics, either.
Governments should be so lucky with keeping thier secrets.
Thx-RM
I'm particularly interested in the sampling section. Don't see any reason why after sampling the signal can't stay in the digital domain. A DSP can handle the rest. The output from the DSP can be re-clocked to an standard audio sample rate and bit depth, converted to an SPDIF or I2S and sent to a comp via sound card technology. Common sound card apps can be used.The output would be a fixed frequency placed at the best view in a standard FFT app.
Rick I just found this on Ebay.
shibasoku AD725 | eBay
The link doesn't work. There's new listing on ebay for a 725B manual with schematics.
shibasoku AD725 | eBay
The link doesn't work. There's new listing on ebay for a 725B manual with schematics.
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Too late- I just bought it. I'll scan it and make the file available when I get it. Should be very interesting. He relisted it instantly. . .
Thats great! Thanks davada for finding it and thanks demian for buying it. These things are so hard to get.
I was pretty fast but when I checked - it had not been relisted. Now I am not depressed anymore 🙂
-RM
ShibaSoku AD725C Input Stage Schematics
I have now drawn what I believe to be a close approximation to the input stage schematic (it beats watching the television). I can't identify the input stage part which is marked NEC, A61A, K422 and is in an 8 lead metal can pacakage (TO-99). I haven't included the reed relay drive circuits.
I don't know the answer. It has a phase locked loop on PCB A11 that I presume locks to the input fundamental. The voltage controlled Oscillator (QA9) has some range switching and the loop filter includes a multiplying digital to analog converter. I think that the VCO runs at 6 x the fundamental.
It could sample the harmonics directly or mix them down to an intermediate frequency that is then fed to the Analog to Digital Converter. I think that the system relies on most of the fundmantal being rejected by the notch filter. I can't remember what the Analog to Digital converter is but it is pretty ancient so it might only be able to convert at a low frequency hence all the complexity.
What are we looking at here?? Input from external source generator (via C52) and filtered output to monitor (via R67) ? Or what? They are all upgradable IC's toachieve lower noise and distortion.
Got pictures of NEC part on the pcb? maybe I can match it up with my pcb for identification.
Thx-RNMarsh
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I would wager the NEC is a dual pch Jfet. The stage has input attenuators and gain (up to 80 dB?). The opamps are for driving the frequency counter and the PLL.
Thanks a bunch. Much study awaits.
Thanks a bunch. Much study awaits.