Blackstar HT60 arcing after filter caps

[Rybow]

What do you mean "maxed"? Do they burst in flames? The operating temperature for these resistors may be above 50°C, which is where it starts to burn skin.

By “maxed” I mean the bias & balance trimmers are near the end of the available adjustment, at which point the resistors got so hot that they have melted the PCB underneath & blackened the solder points.

Are you sure? What's the "correct side"? The voltage should be measured across D27, that means one probe on each side, not between ground and one point. In particular, between ground and pin 4, you can only expect residuals. That's between pins 3 & 4 that you need to measure.

I meant the positive side of the diode. I know it says across d27 in the instructions, but the few videos I saw showed people going to ground. If I measure across D27 my meter is pinned to 0.00 mV.

Pins 3 & 4 start at around 1mV, and then there is a slow climb (40 minutes) to 5.1mV where it came to rest (total time I measured for was 1h 20 mins or so). Adjusting the trim pots has no effect on the voltage.

That's about what I would expect to find there
No. Your meter cannot load a 1 ohm resistor. It is normal to see a surge then a stabilized value.

Ok. Good to know.

I am considering getting another matched set of power tubes for testing.

 

[abbey road d enfer]

By “maxed” I mean the bias & balance trimmers are near the end of the available adjustment, at which point the resistors got so hot that they have melted the PCB underneath & blackened the solder points.

The balance trimmer should be in mid position to start with. Then the bias pot should allow varying current from almost zero to too much (plates glowing red).

I meant the positive side of the diode. 

Waht is the positive side of the diode? Cathode or anode? depends how it's connected.

I know it says across d27 in the instructions, but the few videos I saw showed people going to ground. If I measure across D27 my meter is pinned to 0.00 mV.

So there is something wrong; either D27 is shorted or there is no current through it (not very likely).

Pins 3 & 4 start at around 1mV,

Do you mean "the voltage between pins 3 & 4?"

then there is a slow climb (40 minutes) to 5.1mV where it came to rest (total time I measured for was 1h 20 mins or so).

That would indicate only 5mA idle current, way too low.

Adjusting the trim pots has no effect on the voltage.

This is wrong. First unplug the power tubes. What is the voltage at the wiper of the balance trimmer? there should be about 60V, maybe more. What is the voltage on the wiper of the bias trimmer, in both CW and CCW positions?

I am considering getting another matched set of power tubes for testing.

That would be wasting money.

 

[Rybow]

The balance trimmer should be in mid position to start with. Then the bias pot should allow varying current from almost zero to too much (plates glowing red).
Waht is the positive side of the diode? Cathode or anode? depends how it's connected.
So there is something wrong; either D27 is shorted or there is no current through it (not very likely).
Do you mean "the voltage between pins 3 & 4?"
That would indicate only 5mA idle current, way too low.
This is wrong. First unplug the power tubes. What is the voltage at the wiper of the balance trimmer? there should be about 60V, maybe more. What is the voltage on the wiper of the bias trimmer, in both CW and CCW positions?
That would be wasting money.

Sorry for the delay. Been on a bit of a hiatus dealing with adult stuff

Before I went to check the trimmers I replaced R206 & 209. Now these should have been 5% tolerance, but measured out of circuit they were closer to 20% on the low side. I replaced them with 2% 2 watt (best I could get locally) and hit the power. 2 seconds later I heard that sizzle sound that things had gone bad. Immediately hit the power off and looked up in time to see an arc between R206 and R200. R200 being the resistor that’s was completely burned at the beginning of this journey.

I believe that once I replaced R206 & 209 I put the amp back in its original state of failure. The only part that I have yet to replace on this area are the 220uF power supply filter Caps. These caps have a ripple current rates @ 0.92A according to the data sheet. I was going to replace them with a similar rated or higher cap, but thought it best to see if there might be another cause