narayan@BBN.COM> (01/10/90)
I got the Service manual in 10 days, pretty quick I must say. Yes, the manual contains a wealth of information and very detailed. I am not sure who started the rumour, but the front-end FETs which seem to blow ever so often are actually high-performance Si n-channel JFETs according to information posted on sci.electronics. I hope Sony can do something about failure of these devices in future designs. It is a very sneaky problem, difficult to ascertain if you use a long-wire most of the time. ----------------------------------------------------------------------------- Sriram Narayan 810446 Texas A&M University | INTERNET: narayan@photon.tamu.edu | Go Alain Prost! US Mail: X4 Hensel #K, College Station, TX 77840.|
dbraun@BBN.COM> (01/10/90)
Could you describe the circuit in general terms?
I would especially like to know that filters are used in the IF.
Most likely they are ceramic ones by Murata. Mention the part numbers,
and I will look them up in a catalog and post the specs.
I recently bought a Sangean 803A. It seem fine for broadcast listening,
but I think it is weaker for SSB, CW, RTTY, etc. This is because
there is no way to choose between USB and LSB. The BFO frequency
is fixed to be centered in the passband. The "BFO Pitch" knob does
not change this, but is instead a fine tuning control that only
works when the BFO is on. It essentially moves the BFO frequency and
the passband at the same time. The knob is marked with "USB" at one
end, and "LSB" at the other, but you can get both USB and LSB equally
well (at the same time) with the knob in any position.
Also, I noticed (by removing the back) the filtering:
There is a two-element crystal filter in the 55 MHz first IF,
and then a choice of two different Murata ceramic filters at
the 450 Kc 2nd IF. Yes, they used 450 instead of 455 Kc!
The filters are types SFP450I and SFR450K. These are not the greatest,
with only 40dB of selectivity, but you would also have to consider
the selectivity of the crystal filter in the first IF.
You could upgrate the filters much more easily if they were the
standard frequency.
Doug Braun Intel Corp CAD
408 765-4279
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