Traynor (Yorkville) Beta 500

The Traynor Beta 500was made by Yorkville probably in the late 80s or early 90s. There’s very little information I can find in the internet but judging from the supply rails of +- 60Vdc, I can assume the power output is about 250W into 4Ω. I am not sure whether she is a single channel power amplifier or 2-channels of 250W each. I’ll have to open her up to check her innards. Nonetheless, this power amplifier comes in a wooden case and is meant for “Live” performances as opposed to domestic HiFi.

Traynor Beta 500 Power AmplifierFig 1 – Traynor Beta 500 Amplifier Schematic

What struck me immediately when I saw the circuit (Fig 1) is the use of Bi-polar Darlingtons (BDV67D/BDV66D) in the output stage. Paralleling 4 Darlingtons can be difficult because you need to match them. With their high gain, that’s a tall order.

Furthermore, I don’t see the benefits when a normal Bi-polar transistor like 2SC5200/2SA1943 would suffice. If high impedance in the output stage is desired, one can use a Pre-driver before the main driver for high current gain or simply use Hexfets like IRFP240/9240. You will lose a bit of power because to bias them, they need about 5V but they are well suited for PA use due to their robustness.

Another issue I have is the use of mirror image typology. This circuit is more suited for domestic HiFi. For PA use, i would choose something simpler.

When I work on this amplifier, I will abandon this mirror image typology and opt for a single ended VAS. Outputs can be either Bi-polars or Hexfets. Robustness for me is paramount in PA.

Summary

There is a lot of potential to upgrade this amplifier. I am convinced that after I work on her, she would not only sound better but she’ll be more reliable.