"Bob" wrote in message ...
I would guess the PLL is going out of lock. Do a careful alignment.

When the PLL is on the verge, the signal gets distorted and unstable.

If there is no ALC, it's probably because there isn't enough power output to
overcome its threshold.

Just a guess; I've never worked on one of those rigs.

Bob

Hi Bob,
a good theory and got me going - but then I realised it is an analog
superhet, ie no horrible nasty almost digital things. But a valid
point - will look at the o/p of the mixer on the affected bands - the
vfo runs a constant 5-5.5Mhz, so possibly the heterodyne osc. is
playing up - although, a rough check has shown the drive levels to the
PA board are constant irrespective of fault condition.
de VK3BFA Andrew