Wem ER100
From around 1966 - Solid State
This Wem was brought in by an avid Wem collector who said he got it from a guy who used to rent out band equipment in London a couple of decades ago. It came with no mains or speaker plugs and it hadnt been used for a very long time. I gave it a good check over and here's what I found.
The mains primary was fine and the earth bond was good so after reinstating the mains and speaker plugs I fired it up using a current limiting device. The controls were noisy as you would expect and there was some low and distorted output with a guitar which needed investigating.
Although the main filter capacitors measured excellent so were left alone, several of the smaller ones were in poor shape in both the power and pre-amp sections.
A full service and recap later there was the normal background hum and hiss but there was no output at all with guitar!
Checking voltages again I discovered a 560 Ohm power supply resistor had gone open circuit so nothing was feeding the pre-amps. After replacing the dud resistor with a nice Iskra 2 Watt one I had on hand, all was well and a perfect sine wave was observed, delivering around 80 Watts into an 8 Ohm load. As Wem designed thes amps to be used with one of their special 6 Ohm cabinets, I guess it would reach around 100 Watts in that situation, or into a 4 Ohm cabinet.
After letting the amp run a few hours, just in case any other resistors decided to fail, I had the tricky job of putting the chassis into the customer's new custom cab. The materials were a lot thicker than the original so the bolts were only just long enough to to get a nut on the end, using quite a lot of force to get them to meet up!
So where are the knobs! Well I had to totally destroy three of them in my metal work vice to get them off! The grub screws were well and truly corroded in.
The mains primary was fine and the earth bond was good so after reinstating the mains and speaker plugs I fired it up using a current limiting device. The controls were noisy as you would expect and there was some low and distorted output with a guitar which needed investigating.
Although the main filter capacitors measured excellent so were left alone, several of the smaller ones were in poor shape in both the power and pre-amp sections.
A full service and recap later there was the normal background hum and hiss but there was no output at all with guitar!
Checking voltages again I discovered a 560 Ohm power supply resistor had gone open circuit so nothing was feeding the pre-amps. After replacing the dud resistor with a nice Iskra 2 Watt one I had on hand, all was well and a perfect sine wave was observed, delivering around 80 Watts into an 8 Ohm load. As Wem designed thes amps to be used with one of their special 6 Ohm cabinets, I guess it would reach around 100 Watts in that situation, or into a 4 Ohm cabinet.
After letting the amp run a few hours, just in case any other resistors decided to fail, I had the tricky job of putting the chassis into the customer's new custom cab. The materials were a lot thicker than the original so the bolts were only just long enough to to get a nut on the end, using quite a lot of force to get them to meet up!
So where are the knobs! Well I had to totally destroy three of them in my metal work vice to get them off! The grub screws were well and truly corroded in.
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