11-07-2015, 08:24 PM
I wouldn't mind seeing a picture of C1 - it appears to be hidden by the mounting tab of the IC. Just curious - I know it's not really important. I do have decent stocks of Mullard/Philips components from that era here, so might recognise it.
<Digression>
Perhaps surprisingly, it's unusual to measure audio distortion with a spectrum analyser, and practically unheard of back in those days. Most measurements are THD+N, which means a notch filter is used to remove the fundamental, then an RMS measurement is made of the remainder, including noise. Good instruments (e.g. HP8903) will get nearly 100dB of fundamental rejection in the 1kHz region, meaning measurements down to about 0.001% are possible.
In more recent times, instruments that can measure THD (without the N) have come into existence, but obviously they need a high-end ADC and lots of computer processing to perform an FFT. I've got one here - a Tek AM700 - but it doesn't boot, sadly. One day I'll try to fix it. Audio Precision are the default choice if you have the budget. Prism Audio make the Dscope for rather less money if you can bear to use their software (I struggle!). Of course, freeware+soundcard is a reasonable, if uncalibrated route.
Of course, there are exceptions. The HP3580A is a spectrum analyser as RF folk would recognise it, but instruments like these are very rare. We have one at work - it's rather slow and clunky compared to the PC-based solutions, but it has a certain charm about it.
</Digression>
Anyway, all tangential to the original question, but hopefully of interest to some. I have no knowledge of PMR gear, though looking at the pictures provided by Lawrence, it's not much of a stretch of the imagination to make the connection. That said, it looks like a totally "generic" Philips/Mullard construction to me, using their standard parts of the time - really, it's only the glass fibre FR4 PCB material and gold-plated connectors that separate it from consumer-level gear. I've seen identical construction in Philips test gear - though it's clearly less likely to be from that segment - especially with the Pye branding.
Good luck with the search
<Digression>
Perhaps surprisingly, it's unusual to measure audio distortion with a spectrum analyser, and practically unheard of back in those days. Most measurements are THD+N, which means a notch filter is used to remove the fundamental, then an RMS measurement is made of the remainder, including noise. Good instruments (e.g. HP8903) will get nearly 100dB of fundamental rejection in the 1kHz region, meaning measurements down to about 0.001% are possible.
In more recent times, instruments that can measure THD (without the N) have come into existence, but obviously they need a high-end ADC and lots of computer processing to perform an FFT. I've got one here - a Tek AM700 - but it doesn't boot, sadly. One day I'll try to fix it. Audio Precision are the default choice if you have the budget. Prism Audio make the Dscope for rather less money if you can bear to use their software (I struggle!). Of course, freeware+soundcard is a reasonable, if uncalibrated route.
Of course, there are exceptions. The HP3580A is a spectrum analyser as RF folk would recognise it, but instruments like these are very rare. We have one at work - it's rather slow and clunky compared to the PC-based solutions, but it has a certain charm about it.
</Digression>
Anyway, all tangential to the original question, but hopefully of interest to some. I have no knowledge of PMR gear, though looking at the pictures provided by Lawrence, it's not much of a stretch of the imagination to make the connection. That said, it looks like a totally "generic" Philips/Mullard construction to me, using their standard parts of the time - really, it's only the glass fibre FR4 PCB material and gold-plated connectors that separate it from consumer-level gear. I've seen identical construction in Philips test gear - though it's clearly less likely to be from that segment - especially with the Pye branding.
Good luck with the search
