A tube killed my Crack

[TRTim]

I have had the Crack with the Speedball upgrade up and running daily for the past two years. Great sound. The other day I turned it on and the 6080 GEC sparked and crackled. I imediately turned off the amp and replaced the tube (this didn't blow the fuse). I noticed the sound was louder in one side then the other. I looked at the underside and saw that one of the diodes on the main Speedball board and one on the "B" board were not lighting, so I ordered more from your site. I replaced all the diodes on the Speedball main and the "B" board but they still aren't lighting. What should I check next?

Thanks

 

[Tom-s]

Do voltage checks following the Speedball manual.
And report back.

 

[TRTim]

Voltages are as follows:

1- 67.9
2- 84.1
3- 0
4- 82.5
5- 62.3
6- 0
7-68.4
8- 0
9- 55.6
10- 0
11- 0
12- 0
13- 81
14- Unknown (Forgot to write it down)
15-134.7
20- 0
21- Unknown (Forgot to write it down)

Also I noticed that after doing the checks one of the heat sinks on the Main Speedball board were very hot to the touch. The other one seemed just a little warm.

Thanks.

Tim

 

[Tom-s]

There's more to this problem then just the Speedball boards.
Your PS voltages are low compared normal and compared to your post in 2015:

 
1  179
2  180
3  0
4  180
5  77.9
6  0
7  172
8  0
9  112
10  0
11  0
12  0
13  181
15  199
20  0
21  216

 

[diynewbie]

Keep in mind that I am just know trying to teach myself electronics.  But, the voltage at terminal 13 being less than half its value suggests to me that there is something wrong with bridge rectifier part of the circuit - the diodes connected to terminals 19, 20 and 21.  My guess would be that you are seeing half-bridge instead of full-bridge rectification.

 

[Doc B]

As we say repeatedly, the LEDs not lighting is a symptom of a problem that is not the LEDs. It is likely that the tube arcing took out the transistors on the big board. The shorted transistors are pulling the voltage down and also making the heat sink so hot. Replacing the TIP50 and 2N2222A is probably the fix.

 

[Paul Birkeland]

You may also have an insulator issue with the TIP50C (this is suggested by your voltages).  Sometimes it takes some time for this to creep up, so be sure to check the section in the Speedball manual about properly mounting those transistors to the heatsinks.

 

[TRTim]

Thanks all. Can I order the replacement part from Bottlehead?