Valve Itch phono

[Salas]

Use your generator and scope for typical debug procedure then to find the fault.
100mV 1kHz, then attn -40dB, input to SUT each channel after another.
Scope SUT out, 1st stage out, second stage out, see where the signal stops and why.

 

[merlin el mago]

OK I will do tomorrow but it's strange why channel Right don't sounded with the diode.

 

[Salas]

The diode only helps the bias further. Diode's cathode to ground BTW.

 

[merlin el mago]

Yes I connected both cathode to ground.

 

[merlin el mago]

Tomorrow will see what's happened with left channel & diodes. Good night Salas.

 

[merlin el mago]

This morning I powered the Itch but a big sound happened & red led from SSHV2 don't lit: tested the SSHV2 two DN2540 fried, one SK117GR fried, one KSA1381 fried & the three diodes fried. I only have one DN2540 as spare so I need to order more to test the Itch

 

[stajo]

Enoying. Id supply you but its prolly faster with some local provider.

 

[Salas]

This morning I powered the Itch but a big sound happened & red led from SSHV2 don't lit: tested the SSHV2 two DN2540 fried, one SK117GR fried, one KSA1381 fried & the three diodes fried. I only have one DN2540 as spare so I need to order more to test the Itch

Is that the Itch you had made a long ago and was playing OK or some new build attempt?

 

[merlin el mago]

The old one.

 

[Salas]

Can it be something in the build shorted? Weirdly catastrophic for random failure.

 

[merlin el mago]

Only connected & disconnected the SUT...

 

[stajo]

Even a full short on input with colourful arcs did not blow that much in my excursions. Havent tested output yet tho

 

[merlin el mago]

Enoying. Id supply you but its prolly faster with some local provider.

I don't know local or European supplier for DN2540

@Salas could I use a substitute for DN2540?

 

[neskor]

2 x Supertex DN2540N5 DN2540 Depletion Mosfet DIY CCS | eBay

 

[merlin el mago]

Thanks neskor I know this ebay seller (I bought from him) but it's too expensive.

 

[Salas]

@Salas could I use a substitute for DN2540?

No, not really in the reg's cascode CCS. It can turn unstable, not having the right thresholds, parasitic figures, avoid.
Just drop to 300V the raw supply with an RC or LC to work on the Itch itself meantime waiting from Stajo or Ebay etc.

 

[merlin el mago]

Thanks Salas I will use non active raw supply. Wich load have I to use to calculate with PSUDII for B+ 300V?

 

[Salas]

P.S. That is all very weird. Not having a channel suddenly, seeing problems with 18-20K when Revoli had 3.3K for Dyna 10X4, seeing problems with diode trick when neskor could use leaky valves with that successfully, power on burn out on a long servicing build...voodoo stuff.

 

[Salas]

Thanks Salas I will use non active raw supply. Wich load have I to use to calculate with PSUDII for B+ 300V?

10mA for common PSU between channels.

 

[merlin el mago]

Thanks from voodoo country.....