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Wem Control ER15 No.1

Picture

Here is a Wem Control ER15 from around 1964 that was in need of some attention.  Looking over it, the mains transformer had been leaking its wax all over the place  and the main reservoir capacitor from January '64 was bulging and low on capacitance. The output transformer was very loose on its mountings too, and the amp was lacking volume. Someone had already worked on the amp replacing some resistors and a pre-amp smoothing capacitor.

Heres what was done:
  • Chassis given a good clean
  • All bolts tightened down and washers fitted where necessary.
  • Pots, jacks, valve holders de-oxidised and re-tensioned where needed
  • Main filter capacitor changed for F&T  and new power resistors fitted.
  • There was one bad ECC83 which was changed. 
  • Small repair to the cabinet screw holes
  • Changed the shared EL84 cathode resistor and pre-amp cathode bipass caps

A strange thing about these amps is that the phase inverter uses one triode from each of the two ECC83s meaning you really need a matched pair.

The shared EL84 cathode resistor had been previously been changed to a 270 Ohm, so the EL84s were pretty starved.  I changed it to 150 Ohm to bring it closer to where it should be with the modern JJs fitted.You could go lower here too, the Dominator Mk 3 has a 100 Ohm in this position making them run a lot hotter!

Lo and behold there was a huge difference in output power.  270 Ohm is recommended for each EL84 in push-pull, so half that for a pair sharing a single resistor.

The owner was interested in modifying one channel to Marshall specs.  I dissuaded him from this as it requires changing the circuit from original.  Instead, when replacing the cathode bipass cps on the pre-amps, I left one channel stock (22uF) and changed the other to 1uF.  This gives a subtle frequency shift enhancing the treble and mids for a little bit more crunch.

All in all these are very nice amps but the volume pot feeds directly into the 1st stage of amplification so they are noisy.  It's best to turn the amp volume all the way up (no carbon tracks engaged) and use your guitar controls instead.



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  • Repairs & Servicing
    • Guitar Amp Service & Repair
    • Business Card
  • Contact
  • Amps & Stuff
    • WEM / WATKINS >
      • Watkins Clubman
      • Watkins Westminster
      • Watkins Westminster Mk 9
      • WEM Control ER15 No. 1
      • WEM Control HR 30
      • WEM Dominator Mk3
      • Watkins Copicat Mark 2
      • Wem Watkins Copicat Mk 3
      • Wem ER100
      • Wem PA100
    • Baldwin Burns Amplifier
    • Carlsbro CS 60 PA
    • Elpico AC52
    • Leo Fender >
      • Fender Concert Repair
      • Fender Twin Reverb 1977 Silverface
      • Fender Twin Reverb 1972 Silverface
      • Fender Blues Deluxe
      • Fender Musicmaster Bass Amp
      • Musicman RP 112 Sixty-five
    • Gibson >
      • Gibson Mercury
      • Gibson Falcon GA19RVT
      • Lab Series >
        • Lab Series L2 Service and Repair
        • Lab Series L5 100W Combo (Gibson/Norlin)
    • Hiwatt Lead 50R Combo
    • Marshall >
      • Marshall Artiste
      • Marshall Superbass Mk2 100W Head and Cab Service Repair
    • Miscellaneous Amps >
      • Harmony H307x
      • Hotpup 5F1 Champ
      • Impact 60
      • Mystery Amp
      • RSC Bass Major
    • Orange >
      • Orange OR120 1970s Service and Repair
      • Orange TH 30 repair
    • Schaller KV 40
    • Selmer >
      • Selmer Constellation 20
      • Selmer Treble & Bass Mk 2
      • Selmer T&B 50R SV
    • Traynor YGL 3 Mark 3
    • Tripletone Amp Conversion
    • VOX >
      • Vox AC 10 (JMI)
      • Vox AC 30 TB Restoration
      • Vox AC 50 Repair and Overhaul
  • Blog
  • Other
    • Marconi C10A radio
    • Interesting Waveforms