No cheaptunes bank... So many things to do.
But that would be great to have one.
For old school FM sound, use algo 1 or 2 (with 3 operators).
As 6581 suggested, on/off enveloppe, at least on the modulator operator (2 & 3 for algo 1).
Yes, square and triange could sound like what you're after on carriage operator (op 1 for algo 1).
Then try some low IM value.
Setting operator 2 or 3 with noise waveform and very short enveloppe could also produce interesting attack.
Let use know what you find