I've been asked to repair a couple of old car radios, the valve and vibrator type. The vibrator is "vibrating" ok but there is no AC on the 6X4 (removed it as well) or dc on it's output. Checked the buffer condensor, the primary & secondary of the power transformer, they all checked ok. Stripped the vibrator, cleaned the points, readjusted the contacts but still no Ac. What else,apart from replacing it ( NLA) , can I do?
Regards.
Rudy

Are there any resistors or capacitors in the primary circuit? Open series resistors will cease current flow in the primary. Open paralleling resistors (across points) will cause them to pit and become damaged, though the vibrator should energize the transformer for a while. Any condensers across the points that are shorted will keep the transformer secondary from energizing, though you will also probably notice a blown fuse or overloaded power supply, and possibly a smoking transformer.

Check the transformer primary to see if it is receiving pulsating DC. To verify, perhaps look at it on a scope. If it is receiving solid DC, the secondary won't energize.

Inspect the vibrator points. Make sure that they are fully opening and closing. Depending on the kind of vibrator, it may be able to vibrate without sending pulsating DC to the transformer primary. If the vibrator has a separate set of points for the vibrator coil, the moving piece will vibrate regardless of the functionality of the actual power supplying points. If the points are either in a permanently closed or open position, the transformer secondary won't energize. For this type of vibrator the points must rest open, and must close whenever the moving piece swings in the appropriate direction.

Another kind of vibrator uses one of the main sets of points to also control the moving coil. Both sets should be open when the vibrator is at rest. The first set of points to close shorts across the moving coil, causing its magnetism to collapse. At the same time that set of points sends full voltage to its associated half of the transformer primary. Since the vibrator coil magnetism has collapsed, the moving piece (perhaps we could call it an armature??) swings in the opposite direction, opening the set of points that had just been closed, and also closing the other set of points so that the other half of the transformer primary is energized. Since the first set of points is open, the vibrator coil becomes energized again. For this type of vibrator, viberation depends on proper point function (the main set of points), so it is unlikely that this type of vibrator would vibrate without energizing the transformer. Still, be sure that if you have this kind of vibrator it functions exaxtly as described above. If you don't get proper point action, the transformer won't energize properly.

A third kind of vibrator is the synchronous type. You probably don't have this kind of vibrator since a rectifier tube is present.

T.