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PaulM · 23rd Oct 2017, 3:32 pm

You're sort of close with the driver transistor number, it's a BSR59. That's a Darlington device and so far as I can see, it's all good and the pulse drive looks OK, plus the SMPSU output transistor is relatively cool, so running efficiently. The associated transformer runs a little too hot for my liking - is that normal? Bear in mind that this set will be greedier for power than earlier ones. As I don't have the manual (if there ever was one for this variant), I've set the HT to 165V as it seems happiest there and that's in the middle of the adjustment's range. Everything else on the secondary side also then comes out about right too with the width correct and EHT plausible.

I've never seen a SMPSU behave like this - why is it so sensitive to connecting almost anything to the incoming HT line? 3ft of wire and it's fine, connect the meter (no ground wire) and the trip cycles. I can see no clues on the waveforms - they all look about right for this class of supply, and apart from a few 'wobbles' in the width for a few seconds after switch on, it's fine. Very odd indeed.

Cheers,

Paul M

23rd Oct 2017, 3:32 pm	#12
PaulM Hexode Join Date: Nov 2006 Location: Near Lincoln, UK. Posts: 483	Re: Mystery Decca You're sort of close with the driver transistor number, it's a BSR59. That's a Darlington device and so far as I can see, it's all good and the pulse drive looks OK, plus the SMPSU output transistor is relatively cool, so running efficiently. The associated transformer runs a little too hot for my liking - is that normal? Bear in mind that this set will be greedier for power than earlier ones. As I don't have the manual (if there ever was one for this variant), I've set the HT to 165V as it seems happiest there and that's in the middle of the adjustment's range. Everything else on the secondary side also then comes out about right too with the width correct and EHT plausible. I've never seen a SMPSU behave like this - why is it so sensitive to connecting almost anything to the incoming HT line? 3ft of wire and it's fine, connect the meter (no ground wire) and the trip cycles. I can see no clues on the waveforms - they all look about right for this class of supply, and apart from a few 'wobbles' in the width for a few seconds after switch on, it's fine. Very odd indeed. Cheers, Paul M