Speedball upgrade feedback and manual change suggestion

[soonyc]

Hello,
I've finally (almost) completed the speedball upgrade. It seems to work well now (voltages and sound are ok) but I had the "transistor to heat sink short" issue, which seems to be a well known issue, judging from this forum.

What happened is that my fiber washers are different from the ones in the manual (04-23-13)) : they have an extension which is supposed to go through the hole in the transistor and heatsink, isolating them effectively. Unfortunately the diameter of this extension is too large for the hole! So, since there isn't an extension on the washer on the photo in the manual and also no mention that these parts have to be isolated, I removed the extension and used the washer like this.

There aren't any resistance checks for the speedball, so I only noticed I had a problem when I measured 40V instead of 170V and smoke came out near or from the second power supply capacitor!

Luckily for me this problem is well documented on here.

I've taken out the screws and used some wooden clamps to hold the transistors to the heat sinks for the test while waiting for the polyamide bolts I ordered to arrive.


Changing the manual is not always a good idea, but since there have been several reports of people having a similar issue, may I suggest to at least include a resistance check between the small heatsink of the transistor and ground (even if the problem may only appear with the heat)
or to mention in the manual that the small heat sink of the transistor has to be isolated from the big one?
I know it's part of the DIY experience to make errors and to learn from them, but in this case I'm afraid the stress the amp has suffered from the short has significantly reduced the lifetime of the capacitors, resistors and transformer. I prefer more testing and less repairing 

We will see for how long I can use it before troubleshooting again.
Even so I'm very happy with the Crack and speedball. I liked building it and learning. It's a great amp!

Thanks to everyone at Bottlehead!

[mcandmar]

What happened is that my fiber washers are different from the ones in the manual (04-23-13)) : they have an extension which is supposed to go through the hole in the transistor and heatsink, isolating them effectively. Unfortunately the diameter of this extension is too large for the hole!

That's not good, sounds like the something has changed in the manufacturing of those parts.  The plastic insulator has always had a raised section that sits inside the transistor, its purpose is to prevent the screw from contacting the metal tab as it goes through.

Can you post the part number of the mounting kit, and the brand of TIP50 transistor you were supplied as it may help the BH guys narrow down the problem. Pic of the insulator would be good too.

[Paul Birkeland]

What happened is that my fiber washers are different from the ones in the manual (04-23-13)) : they have an extension which is supposed to go through the hole in the transistor and heatsink, isolating them effectively. Unfortunately the diameter of this extension is too large for the hole!

Can you post a photo of what you're describing?  We have an enormous back stock of that particular part, and I used a few last week with no issues.  The washer doesn't necessarily need to go through the hole in the heatsink, you can let is pass through the transistor, then crank it down nice and tight.

The shorting issue has always been an issue of not following the directions regarding installing the hardware between the TIP50 and the heatsink. 

[soonyc]

Ok, know I understand! I remember that I managed to put it through one hole but not both. I didn't think of cranking it.
I must admit I didn't try too hard either because I was sure that this raised section wasn't that important since it didn't show in the manual.

The important thing is to tell people to look out and be sure their transistor is well isolated before they power their amp on.