Krell KBL & KPA

[VintageAmp]

I have a KBL back on my bench. It seems the 15030 and 15031 keep failing. Does anyone have an idea about the selector switch in the power supply? S1 = 2 S2 + 1 and S3 = 1 Is this correct for 120 Vac operation? Since the output V out is +/- 77 Vdc I am beginning to think the XFMR tap is incorrect. The first set of transistors mounted to heat sinks get scary hot (in the power supply) but the unit seems to work fine other wise. Distortion and offset test fine.

[VintageAmp]

I decided to run the unit on a 100V autoformer and it has been operating for 6 months without failure. Power supply heat is way down.

[h_a]

The first set of transistors mounted to heat sinks get scary hot (in the power supply)

Sounds a lot like a regulated supply running from the wrong windings. Try to measure the secondary voltages with a multimeter, should be a tad higher than the rails (maybe 10V or so).

Have fun, Hannes

[VintageAmp]

The power supply has 2 stages for each supply.
77V +/- rectified gets regulated to:
58V +/- and then gets regulated to:
48V +/- as it goes to the preamp. On the preamp board it gets regulated to 44V +/-

The other supply starts at 48V and ends at 21V after regulation.

I have checked the taps and confirmed the taps are set correct to 120 V operation. If I change the taps I get 220 V

[VintageAmp]

As of 1/12/12 the unit is still running at 100 VAC with no trouble.
Sound quality is very livable in the daily system. Cannot say its better then the Threshold T2 I use in the main room, but it is = or better then some older Thresholds. At any rate, they ALL need new caps.