Blackstar HT-60 Stage schematic

[Enzo]

Oh I forget now, as it doesn't really impact me, but the extra stripes mean things like temperature stability.

Looking it up, orange appears to mean 15ppm/K

So for each degree Kelvin in temperature change, the resistance can change 15 parts per million.


But it is also possible they meant it to mean power, as orange is 3 and it is a 3 watter.

[J M Fahey]

Enzo, you are bright indeed

Nowadays itīs impossible to tell power dissipation just by body size, just bought some 330ohm 2W metal film and they look like 1/4 Watters from the nearly 70īs , and nthereīs no space to print wattage , so a dedicated band makes a lot of sense.

[Mikestorm]

a little update

yesterday i found a 22k 2watt resistor, i connected in parallel to the burnt existing one with alligator clips, the amp worked but after one minuts the resistor started to change color... still shows the 22k but gets very hot. I know that it have to be 3w, but i supposed that for a quick try it would last a couple of minutes more...

Tomorrow i will go around to find a 3 or 5watt, as the sch shaws, this resistor feed onle the preamp tubes, maybe can be a fault tube?

please let me know

[alexradium]

a little update

yesterday i found a 22k 2watt resistor, i connected in parallel to the burnt existing one with alligator clips, the amp worked but after one minuts the resistor started to change color... still shows the 22k but gets very hot. I know that it have to be 3w, but i supposed that for a quick try it would last a couple of minutes more...

Tomorrow i will go around to find a 3 or 5watt, as the sch shaws, this resistor feed onle the preamp tubes, maybe can be a fault tube?

please let me know

i'd pull off the preamp tubes and monitor the current on that resistor,it could be the filter cap going short.

[Mikestorm]

thanks alexearium

i will, is any type of check that i can do on the cap with a normal multimeter in order to see if is shorten as you wrote?

[g1]

You would have to disconnect at least one leg of the cap and check the cap's resistance reading.
Then while it is still disconnected, also measure the board resistance at the pads where the resistor connects.

[Enzo]

But temper that with the knowledge that your meter works at a volt or two, and these caps work in a several hundred volt environment. Caps that seem OK at a few volts can leak like a screen door over say 100 volts.

When the circuit is live, what is the voltage on each end? What is it dropping, and to what? That may give us a clue as to the cause.

[Mikestorm]

Thanks Enzo and G1

I think i found the cause that keep burning the resistor

The board

C143

C142


a dead cap, c143, as the schematics show is the filter cap just after R204.

I hope there isnt other components to change...

[Mikestorm]

Enzo i checked the "bad capacitor" the one leacked, and i checked the "good capacitor", well... the two seems good, no continuity so no short, and charges and discharges.

But as you wrote, this test is with a normal multimeter at low voltage, maybe at 280 or so volts, things changes

By the way i'm going to change c142, the good one, too

any advices?

[Enzo]

Let us know what happens.

[alexradium]

Enzo i checked the "bad capacitor" the one leacked, and i checked the "good capacitor", well... the two seems good, no continuity so no short, and charges and discharges.

But as you wrote, this test is with a normal multimeter at low voltage, maybe at 280 or so volts, things changes

By the way i'm going to change c142, the good one, too

any advices?

as you can see the liquid went over the board,that's the best sign of failure,i recommend you to clean the area with alcohol.
Once you have completed the substitution check out if all the currents are as expected

[Mikestorm]

Hi

Amp fixed!

I replaced C142, C143, R204

Voltages across C142: 387v
Voltages across C143: 252v

R204 measure 23k.

R204 after two hours of playing at half power was a bit warm by the touch, but not hot.

I think the surgery its been a success!!!

The liquid from C143 have corroded its connection to R204, and started to corrode the ground track too...

Thanks to all for the support and the help.