LEDs replacement

[greyhamster]

I swapped the 12AU7 when the amp was on. I think 3 of the LEDs on the big PCB are dead. Can I used other LEDs for replacement?
I have leds which specification are 3V - 15mA - 2.5 mcd

 

[Paul Birkeland]

I swapped the 12AU7 when the amp was on. I think 3 of the LEDs on the big PCB are dead. Can I used other LEDs for replacement?
I have leds which specification are 3V - 15mA - 2.5 mcd

I'd recommend posting your voltages.  I am somewhat doubtful that you have bad LED's, but also quite certain that you have shorted transistors.

Depending on your voltages, you may need to replace the entire Speedball.

 

[greyhamster]

I have disassembled the big PCB board so I cannot get the voltage measurement now. However I remember the voltage at B+ on the big PCB (terminal 2) was 175 and the the black wire to terminal 3 was 0. Terminal 7 was 0 (2 leds were dead), terminal 9 was 75

 

[Paul Birkeland]

At this point, you can try to check the transistors for shorts between each pair of legs.

The 3V red LED's will absolutely not work in any position in the Crack/Speedball.

 

[greyhamster]

At this point, you can try to check the transistors for shorts between each pair of legs.

The 3V red LED's will absolutely not work in any position in the Crack/Speedball.

Thank you Paul.
I check but find no short.
And I can be sure that the leds are dead by checking them with a digital multimeter.
Should I order some HLMP-6000 LEDs or is there any chance that there are other bad parts too. How can I know that? 
In which scenario do i need replace the entire Speedball?

 

[Paul Birkeland]

In which scenario do i need replace the entire Speedball?

By hot swapping a tube, you have introduced a failure mode that none of us have yet experienced.

You can run the Crack with just the 12AU7, and just the small green PC boards hooked up to test their functionality.

On the larger PC board, I would replace everything.

The HLMP-6000 is the part of choice, with generic 1.5V red LED's functioning reasonably well in the circuit, though not as well as the HLMP-6000 will.

 

[greyhamster]

In which scenario do i need replace the entire Speedball?

By hot swapping a tube, you have introduced a failure mode that none of us have yet experienced.

You can run the Crack with just the 12AU7, and just the small green PC boards hooked up to test their functionality.

On the larger PC board, I would replace everything.

The HLMP-6000 is the part of choice, with generic 1.5V red LED's functioning reasonably well in the circuit, though not as well as the HLMP-6000 will.

Thanks Paul,
I finally test the whole amp and find out that there are only 2 bad transistors and 2 LEDs which all on one channel. I consider myself lucky this time. I was testing a DAC and i didn't even know that the amp was on when i pull the tube out.

 

[Paul Birkeland]

I am relieved that it was an accident. 

 

[NightFlight]

The HLMP-6000 is the part of choice, with generic 1.5V red LED's functioning reasonably well in the circuit, though not as well as the HLMP-6000 will.

By reasonably well, are we talking about tolerance or performance? I have some 1.5v generics lying around somewhere I believe... I would like to test while I wait on an replacement HLMP-6000 from BH. I'd order local but its $20 shipping for a $0.65 part.

 

[Doc B]

The HLMPs were chosen because their performance is more consistent at lower current levels than most LEDs.

 

[Paul Joppa]

The HLMPs have some other technical advantages as well. Incidentally, they are on of the oldest formulations, "standard red". As such their voltage drop is smaller than other red LEDs, and the voltage drop is what sets the operating point. To get as-designed performance, some nearby resistors would ideally have slightly different values.

 

[NightFlight]

No doubt. Its those selections that get you the big bucks Doc. 

Trying a little red domed resistor that has a drop off around 1.6v and a draw of around 20mA.... I hope.  Put it in the wrong way the first time after clipping the ends.  What a bitch to pull back out again. I should have just waited for the part.