This is common problem with Wurlitzer electric pianos which is often attributed to a defect in wiring or another electrical issue. Much more often it is because a reed is misaligned in the reed bar, causing it to touch the pickup. This creates a short or grounding, and can cause hiss, pops, bangs, and sometimes no sound at all.
Fortunately it sounds worse than it is and the solution is relatively simple. Disconnect the power, open the lid, remove the hum shield, find the offending reed (this may take a little bit of time), and realign the reed so it is correctly placed. It is very important that the reed is positioned exactly in the centre of the pickup, so it will not touch the reed when struck by the hammer. This will give the reed a well rounded tone as well.
If this does not solve the problem then it is time to investigate the amp. Older components such as electrolytic capacitors, transistors, and ceramic resistors can often cause hiss, pops and crackle. This is much more invasive and will be explained in another post.
