Here's the preamp section of the Electar Zephyr as it looked upon arrival at the repair shop.

After replacing the filter caps and AC cord, we fired up the amplifier, injected a sine-wave signal, and checked the amp's performance.

We discovered three stage-coupling capacitors that leaked direct current, as evidenced by DC voltages in purely AC circuits.

Such leakage can cause waveform distortion and potentially damage parts, so we marked the bad parts for replacement.

We replaced each of the leaky Aerovox .05 μF 400 V paper and wax capacitors with a .047 μF 600 V ‘Orange Drop’ cap.

Near the end of our restoration, we discovered that, at louder volume settings, the speaker's voice coil made nasty rubbing noises.

So, we sent the speaker to a reconing service to have all its moving parts replaced.