Blackstar HT Stage 60 / Need help on strange noise issue

[x-pro]

-2.6V when standby is off

should be U(b-e) + U(D15 3-1)= 0.9+1.25

[FredPhil]

This is what you got from the measurements.
That's not right.

I might have done wrong on which probe from the voltmeter on which pin on TR4. I got these measurements by putting the red probe always on e. Black probe (COM from the voltmeter) went to b or c for the 2 measures.

The emitter of transistor TR4 is accurately probed at TP14, TP15 ?

Sorry, what are TP14 and 1P15?

[x-pro]

common

[x-pro]

it must be, because according to the datasheet of the transistor, its b-e voltage is 0.9V. (https://static.chipdip.ru/lib/725/DOC028725341.pdf)

[x-pro]

How much does the voltage change on pins 1 and 3 of CON1 relative to Common of course when the standby is turned on?

[Helmholtz]

TR4 emitter is connected to ground. So that's where your black meter lead should go.
Base and collector voltages should read negative.

[Helmholtz]

How much does the voltage change on pins 1 and 3 of CON1 relative to Common of course when the standby is turned on?

With TR4 removed the grid bias will not change with standby, but should stay at a large negative voltage (maybe something like - 80V).

[FredPhil]

PIN1 : -50V on standby, -51.5V standby off
PIN3 : -50V on standby, -51.2V standby off

[Helmholtz]

PIN1 : -50V on standby, -51.5V standby off
PIN3 : -50V on standby, -51.2V standby off

With or without TR4?

[x-pro]

TR4 is at least partially shot.

It is better to replace it. The device can show its operability at low currents.

[x-pro]

It's time to end the tambourine dance.
There is an easy way to check the standby mode.
You need to unsolder TR4 and temporarily replace it with a simple switch. Solder it in the right places where the k-e is.
Then check the bias current on D27.

You don't even need to unsolder the TR4, you can solder directly to its pins.
The only thing is that when switching the auxiliary switch, you need to disconnect the common power supply to avoid accidentally burning the half-dead TR4.

[FredPhil]

TR4 emitter is connected to ground. So that's where your black meter lead should go.
Base and collector voltages should read negative.

OK, my mistake. So the measures read when on standby, from emitter:
- base = -240mV
- collector = -880mV

With Standby OFF :
- base = -2.14V
- collector = -2.78V

With or without TR4?

With.

But from what you're saying, it seems that the next move now is to change TR4 and test again if I still get this bias current on standby, AND the crackling noise when using the amp.

[Helmholtz]

You need to unsolder TR4 and temporarily replace it with a simple switch. Solder it in the right places where the k-e is.
Then check the bias current on D27.

That's a good idea.
But I think testing with TR4 and power tubes removed (post #27 ) will show everything we need to know.

[FredPhil]

So you're saying I should:
- remove TR4
- remove power tubes
- check voltage on every PIN of both power tubes (related to ground, I suppose)

Should I do this on standby or not? What measures should I get?

[Helmholtz]

So you're saying I should:
- remove TR4
- remove power tubes

Yes.

- check voltage on every PIN of both power tubes (related to ground, I suppose)

Yes, but we need only control grid (g1) voltages.

Should I do this on standby or not? What measures should I get?

I expect no difference between standby on or off with TR4 removed.
As said before, it should be a large negative voltage, i.e. significantly larger than - 50V.