Gallien Krueger MB 150 Mains Transformer Replacement

The Gallien Krueger MB 150 is a popular bass amp, especially with double bass players. We recently had an MB150 in for repair with a blown mains transformer, GK part No. TTO-10879-02 (equivalent to TTO-10879-01). Unfortunatley, sourcing a replacement was tiresome. The UK distributor quoted 6 months lead time!

I couldn’t find an off-the-shelf mains transformer that would do the job, so got in contact with Tiger Toroids to get a custom unit made. Amazingly, Stephen at Tiger Toroids already had the specs to make a replacement.

Custom replacement mains transformer for the GK150 made by Tiger Toroids with correct colour coded connectors.

Due to construction contraints, the replacement transformer (see above) is slightly taller than the original (a good thing electrically). However, space in the MB150 chassis is tight, so we could not mount the tranformer safely using the stock mounting plate. You must NEVER allow the mounting bolt through the centre of a toroidal transformer to touch the top and bottom of the chassis; this will make a shorted turn and the transformer will be destroyed in short order.

Mounting transformer with original mounting plate

Thus we filled the transformer centre hole with epoxy potting compound, and drilled a hole for mounting through this. We could now mount the new transformer into the chassis without danger of the bolt touching the both sides of the chassis. If I need to order another MB150 transformer from Tiger Toroids I’ll get them to do the potting.

Centre potted mains transformer now mounts safely in the chassis.

I added a plastic sheet on top of the transformer for extra insulation.

The amp is now working correctly

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