Bush VHF61 'half resto' repair

[Pilot Mariner]

Originally Posted by Techman

An interesting theory. I did wonder if the drifting was caused by more of a physical thing rather than an electronic cause - although you could still possibly argue that this was still 'physical'.

My VH61 has been on for a few hours now and is rock solid with no further drifting, as is normal with this set. You'd think that bad grommets would be continuously varying and causing small movements over all that time, but certainly something to think about and possibly investigate further.

My theory is that the dial cord goes round the far end pulley (which is firmly attached to the chassis via its support), and the drum, obviously part of the tuning assembly. When the tuning knob is turned the whole tuning assembly moves on the perished grommets. When a station is tuned in, the tuning assembly slowly starts to return to its natural resting position unopposed by the perished grommets. The only "give" being small rotations of the drum hence causing the drift. If the grommets are really shot you can see this happening.
You could try wedging bits between the tuning assembly and the chassis but in the end I prefer to do a proper job which is quite involved.

[PaulR]

Originally Posted by PaulR

I have to say that mine drifts rather on FM as it warms up. I have a second one on the shelf waiting to be done so it will be interesting to see how stable that is

Having recently bought a Philips wobbulator I thought I would check the FM discriminator alignment. It was quite a way off and adjusting it (albeit without being able to get a 10.7 MHz marker) has generally improved things. It has been running for an hour or so now with much less drift.

[Leon Crampin]

The grommet theory could be verified by tuning a weak MW station at the HF end of the dial (within the rather poor AM capabilities of this set). If it shifts off tune on AM, it's probably the grommets.

Leon.

[Mr 1936]

Hi

I suspect that the drift is still there but realigning the detector has widened its acceptance range and reduced the need for retuning.

[PaulR]

Yes, that is what I thought. The drift is still there but apparently much reduced.