Amplifier:
Royal Eleking 70 – A rather rare japanese tube amplifier from the ’70s!
Fault description:
Loud buzz when standby was flicked. Reverb does not work, tremolo does not work. Some wires had been cut by the previous owner, and will need to be reattached or replaced.
Procedures:
The loud buzz was an obvious filter cap failure. A very prominent 100hz hum. All electrolytic capacitors were replaced with modern electrolytics or film caps where possible. The power cord was replaced with a modern three-prong one and the chassis was grounded properly.
The cut wires gave a worthy challenge. Initially I only noticed the reverb and tremolo circuit having been cut off. Inspecting further, just one input was intact. All controls were out. Both channel controls and EQs, reverb tank and controls, tremolo circuit, all had their wires either clipped short or removed completely.
For a rare amplifier from The 70s, finding matching schematics can be a reach. Luckily the amplifier has lots of cousins from the same era, either Royals or Elks.
Rebuild was made using a few references from Dr. Tube’s excellent schematic library. Special thanks to Hans Wessels for tracing Elk Twin Amp 50 (EB-202S)! Turned out the only differences between The Royal Eleking 70 and The ELK Twin Amp 50 were the bias circuit and rectifier.
The reverb was dead due to bad solderwork on the tank (and obviously the missing wires). Resoldering the leads and wires got things up and running again. The tremolo circuit was quite unique. In the end, the tremolo was out of business due to one misplaced capacitor (plus the missing wires).
An odd feature of the amp was using tube halves from different tubes as a phase inverter.
Final touches: cleaning and lubricating all potentiometers, new power tubes, biasing. This is a clean amp that sounds quite unique, in a good way. Aggressive short-tailed reverb, tremolo is intense. A very cool guitar amp, phenomenal for keyboards.
Conclusion:
Taking this amplifier on was mostly out of interest and respect for this piece of tube amplifier history. The amount of time and labor spent on this fella was simply absurd. Yet, as an experience, absolutely golden. Had I the possibility to reconsider, I wouldn’t.