Gallien Krueger MB 150 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 trying to source a replacement was tiresome. The UK distributor quoted 6 months lead time, and the only other supplier I could find was in France; they didn’t have the transformer in stock either.

Unlike some other amps (eg Ampeg SVT 350) I couldn’t find an off-the-shelf mains transformer that would do the job, so got in contact with Tiger Toroids who have done several jobs for us over the years to get a custom unit made. Amazingly Stephen at Tiger Toroids had been sent a blown MB150 transformer a few weeks before us, and 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), but space in the MB150 chassis is tight, so this transformer could not be mounted safely using the original mounting plate; what you must NEVER do with toroidal mains transformers is allow the mounting bolt through the centre to touch the top and bottom of the chassis as this will make a shorted turn and the transformer will be destroyed in short order.

Mounting transformer with original mounting plate

Alternatively we can partially fill the centre hole in the transformer with potting compound, and drill a mounting through this. The transformer can now be bolted into the chassis without danger of the bolt touching the other side 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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