12-07-2015, 11:19 AM
Looking at the -ve end of C6, I can see why Ref saw rivets. Obviously, you have it in your hands, but from the pictures, I'd have said rivets too. Either way, it seems extravagant at a glance, especially as the layout doesn't appear to use tracks on the component side, but then many of the other PCBs in the PMR gear linked earlier are double-sided, so it's no hassle. Mind you, I remember Philips using rivets instead of PTH in their (very expensive!) CD players in the mid '80s. And a major source of trouble they were, too 
I've got a lot of those square ceramic jobs, though mine are mostly yellow. The largest value I have is 22n, and it's sensibly labelled "22n" rather than 223 or similar. They do go up to higher values IIRC.
7n5 gives a -3dB point of 125Hz if 750k is assumed for IC1. Or 96Hz if IC is o/c. Closer to your measurements, I suppose, and for comms purposes, going any lower would be a bit pointless. Interestingly, C6 has its pole at 16Hz when working into 15 ohms, so I wonder why they didn't save a few pennies and reduce it to 100u (106Hz) or 150u (70Hz) or even 220u (48Hz)? Either way, easy to increase C1 if needed in whatever application you put this to.
Those Ferrograph test sets were lovely. Manually-tuned notch filter, as was common then, but capable of decent depth. That's a fascinating picture, Lawrence - do please tell more
I've got a lot of those square ceramic jobs, though mine are mostly yellow. The largest value I have is 22n, and it's sensibly labelled "22n" rather than 223 or similar. They do go up to higher values IIRC.
7n5 gives a -3dB point of 125Hz if 750k is assumed for IC1. Or 96Hz if IC is o/c. Closer to your measurements, I suppose, and for comms purposes, going any lower would be a bit pointless. Interestingly, C6 has its pole at 16Hz when working into 15 ohms, so I wonder why they didn't save a few pennies and reduce it to 100u (106Hz) or 150u (70Hz) or even 220u (48Hz)? Either way, easy to increase C1 if needed in whatever application you put this to.
Those Ferrograph test sets were lovely. Manually-tuned notch filter, as was common then, but capable of decent depth. That's a fascinating picture, Lawrence - do please tell more
