Blackstar HT Stage 60 / Need help on strange noise issue

[FredPhil]

R143 is the blue one on the left, a 3W resistor. It's new since I replaced it last week when I replaced TR1 and TR2 (above on the image).
Since it's the only one that has this issue and only on one pin, I figured it could be a problem with the board itself where the solder does not "grip" (in lack of a better term...) enough and gets loose when heating.
The stains you might see on it are due to the fact that I used a plastic pencil to move it when hot, and the plastic got a little bit hot as well...

[Helmholtz]

Moving a loose end of R143 should make lots of noise.

Anyway I would try a new V3.

[g1]

Maybe it's not the correct term, but are you getting what I mean (i.e. contact caps on each end)?

Yes, I think I know the type. Metal caps with the leads (under the paint), sort of like solder-in 3AG fuses.

[Helmholtz]

Yes, I think I know the type. Metal caps with the leads (under the paint), sort of like solder-in 3AG fuses.

Actually most resistors have contact caps.

[Helmholtz]

R143 is the blue one on the left, a 3W resistor. It's new since .

The second color ring doesn't look red anymore.

[g1]

R143 is the blue one on the left, a 3W resistor. It's new since I replaced it last week when I replaced TR1 and TR2 (above on the image).

It's supposed to be a 22K, is it?. If it is, the discoloration of the bands means it is running much hotter than R142 which should not be.

[Helmholtz]

What are the voltage drops across R142/R143?

[The Dude]

It's supposed to be a 22K, is it?. If it is, the discoloration of the bands means it is running much hotter than R142 which should not be.

^^^^^^ that. It looks like possibly the wrong value resistor was installed.

[Jon Snell]

When I replace TR1 & TR2 I replace the two 22k 2W resistors as well.
They are then mounted 1/2" off the PCB to avoid any/further heat damage to the board and prolong the life of the amplifier.
The newer versions use 27k as they dissipate slightly less power. TR1 & TR2 don't need to be driven so hard in the first place on these smaller amplifiers, considering that this driver is used in the four valve output stage right down to the 12BH7 output stage, they do draw too much current, in my oppinion.

[FredPhil]

I did try with a new V3 but it didn't change anything.
You're right, after sending you the picture I realised the rings had faded (due to the overheating?).I replaced it with a brand new one to be on the safe side. The faded one still reads 22k, though...

When I replace TR1 & TR2 I replace the two 22k 2W resistors as well.
They are then mounted 1/2" off the PCB to avoid any/further heat damage to the board and prolong the life of the amplifier.

I did replace the 2 22k 2W resistors after replacing TR1 and TR2, but good advice Jon, I'm mounting them 1/2" off the PCB.

[FredPhil]

OK, with new resistors, I have around 140V on R142, and 182V on R143...V3 is new (and I have the same result with the previous V3, btw). Is this difference normal? If not, could it come from the fact that during all these testing operations maybe TR1 and/or TR2 failed?

[x-pro]

What's at the output of the amp - speaker, resistor, or nothing?
What are the voltages on R140 and R141?

[FredPhil]

R141 = 110V
R140 = 116V
Amp is plugged into its standard speakers

[x-pro]

Also please measure the voltages of R153 and R154.
Of course constant voltages and without signal.
And measure the ratings of resistors R150 R152, when the amplifier is switched off. You can do it directly in the circuit without unsoldering.

[Helmholtz]

OK, with new resistors, I have around 140V on R142, and 182V on R143...V3 is new (and I have the same result with the previous V3, btw). Is this difference normal? If not, could it come from the fact that during all these testing operations maybe TR1 and/or TR2 failed?

V3-B draws too much current. Something must be raising its grid voltage.
Could be a leaky C118 or C116.
To test, lift one end of the cap and see if the voltage across R143 reduces.