Does anyone know how I can convert the output from a speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so the
winding ratio of the transformer should be in the order of sqrt 100 is in
the order of 10 to 1. So you would have to find any (small )tansformer with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms the
transformer ratio would have to be in the order of sqrt 50000/10 = sqrt
5000 = approx 70.

If you can't find an audio transformer for this application , just try a
small power supply transformer ,since these will pass the low freq audio sig
used for SSTV.

Good luck

Frank GM0CSZ / KN6WH