[allan]

Thanks Ian.
I put the HP in the workshop ready for use but nothing seems to be inviting me to use it so I carried out an experiment.
I used my spectrum analyser tracking generator set to 100Hz span and 0dBm output and measured the maximum frequency the HP frequency counter could handle. It could just manage 715MHz feeding the tracking generator into the counter input.
I finally found my spare RF output transistor for my Wavetek 2407 which starting giving trouble (which is why I bought the HP) so I'll fit that and carry out some further tests. The Wavetek covers 10KHz to 550MHz and uses push buttons so doesn't have complicated gears and mechanical contrivances.
Whether the new transistor (SRFT3034) will fix it is anyone's guess. It's similar in shape to the original MRF839F, but it's possible the fault is a dodgy tantalum capacitor...
I might start another thread...
73 Allan G3PIY