The BR-549 Twelve

The BR-549 Twelve Amp

Combo amps are always handy and when they are also light and compact then they are hard to beat. If you can create one with those qualities and also make it sound good then your really hitting all the sweet spots in tube amp technology. This one checks off all three boxes…

 

When I built this amp I had taken a liking to the 5879 Pentode as a first gain stage in some of my small amps. Coupling that to a 12AX7 long tail pair phase inverter and then finally using a pair of 6Y6GT output tubes in push pull gave me a great low amperage big sounding amp.

This circuit is really simple and I’ve found that I prefer the minimal controls on the front panel. For those familiar with the Trainwreck amps you’ll see that I borrowed my treble and bass controls from the Songwriter 30 amps. The purpose of this design is to impose a minimal signal load on the circuit and still have some control over the amount of treble and bass that was pushed to the power stage of the amp.

 

The low power output amps I’m building typically don’t require heavy iron (transformers) and allow me to keep the overall size and weight of the amp down. The other added bonus of using small iron is that the cost is quite a bit lower as well.

 

This chassis layout and circuit board is just about as minimal as they come.

 

 

For the combo cabinet I wanted to not only keep it compact and lightweight so I tried an 8″ speaker for this build. I designed a reflex horn system to bump up the lower frequencies coming out of the front of the amp. If I did anything different with a second generation version of this amp it would be to maybe stretch the cabinet enough to use a 10 inch speaker.

 

Among the challenges in making a small combo amp with a sealed cabinet is to find a way to keep the tubes exposed to some fresh air to avoid a meltdown around the hot tubes.

As the final touch for this amp I gave it a relic finish and a wicker grill cloth to give it that old vintage look. I also designed a bit of a slope to the front panel and fabricated handles into the cabinet.