Many years ago I bought a Manor Supplies TV colour bar/test pattern generator kit, Both timebase generators were bipolar 555. It was impossible to set up the 15,625kHz horizontal timebase so it didn't drift all over the place - in the end I built a TTL timebase divider with 10MHz master clock. On paper - the bipolar 555 is good for 200kHz, in practice they tend to get a bit flaky not all that far above the audio range. The output rise and fall times start to deteriorate about there too.This is from the Signetics Analog Applications manual for NE/SE555:
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The Nat Semi datasheet implies that 100kHz is typical:
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AFAICR: the CMOS 555 is good for 2MHz (on paper anyway).