Valve Itch phono

[merlin el mago]

Originally Posted by Salas

But you got an operating led. 1mV through 10 Ohm TP means 0.1mA. How it can operate the Vref's CCS to set 300V and light the LED? Fishy measurement. Is the sink getting warm?

Both heatsinks cold

[merlin el mago]

Now are warm.

[Salas]

How come? You mixed some other semis?

[merlin el mago]

Not, only Q1. Not warm to hot, is warm to cold.

[merlin el mago]

I ordered Tea-Bag more DN2540, now I will check the zeners.

[merlin el mago]

Both zeners without continuity both poles.

What I have to do:

-Replace the zeners & check the current?
-Wait to new DN2540 & replace zeners & DN2540 to test the current?

[Salas]

To properly test a Zener we need a higher DC voltage source than its value, a protective resistor, then we measure if it meets its value. A little circuit in other words.
I would dummy up the reg load, wet the TP pads with some solder to be sure they conduct to the probes well at all times, and test it in isolation to the Itch for components, oscillation with the scope, different power source or grounding, such stuff. All those data up to now are contradictory. Once it conducts showing well on TP but does not trim CCS there is a bricked trimmer, then it shows 0.1mA but its Vref and led works and 300V voltage is set that needs over 2mA to work in itself and there is some warmth even, then some zeners seem burned but not sure, then some DN2540 changed but not sure of their condition etc. Still there was never smoke. Can't draw a conclusion. DN2540 are like JFETs and can be tested for IDSS by the way, expecting rough 150mA range. You did well to get some even for spares if those you already got will prove good. They are very useful with tubes in general. So gather some certain experimental data, and if there is a defect in parts it will stand out with exchanging. How it played music without ripple hum and sets to an output voltage its perplexing nonetheless. I would also try a different C1. I hope it isn't like the other one you had once that its belly was conductive to the extra pads.

[merlin el mago]

Thanks again for support Salas, I will wait the new DN2450 to be sure and I will solder TP pads to be sure for conductivity. I keep the schematic how to test 12V zeners

[merlin el mago]

Followed in Power supplies forum Simplistic Mosfet HV shunt regulator

Simplistic Mosfet HV Shunt Regs

[merlin el mago]

Fixed and posted some pics in SSHV thread, I post also here