Vintage Tube ULTRALINEAR Amplifier Seeburg MRA5-L6
Thursday, October 31st, 2024
This is an MRA5-L6 tube amplifier. These were HiFi amplifiers (Ultra-linear type) which came out of Seeburg Juke boxes in the USA from the 1950′s era. This one was re-tasked in the past to be a Guitar practice Amp in the USA, but it is just as readily a mono HiFi amp. The oddity about these is that their power transformer never had the facility to run the tube filaments, these were powered by a separate transformer in the Juke box. However this amplifier has had its power transformer replaced in the past with an American unit which does run the tube filaments. But it makes it a 115V line powered amplifier, fine for the USA but to run it here in AU you would need a 230v/115v step-down transformer from Jaycar. The type that passes the Earth through, so the chassis remains Earthed. Other interesting features, the amplifier has an optional automatic volume control, this was to level the volume of many different songs from 45 RPM records. The amp has had some parts replaced in the past, currently it has a good set of electrolytic capacitors. I powered it and played my guitar through it, it works with good sound output. It may require some future repairs, for example I can see that there are a few original capacitors that have not been replaced yet. Tube amplifiers, such as this, or any Tube guitar amplifier, have very high voltages inside, at least 400V as well as the line voltage and are dangerous. There is nothing dangerous on the top, electrically at least, though the tubes get quite hot. And as noted above, the chassis should be earthed.
