Speedball upgrade problems - [solved]

[sadkins]

Having trouble with the speedball upgrade.

First off I'll say that I initially installed the MJE350 transistors backwards (didn't read forums and took the wrong guess as to which way to install the non-metal backed version).  Ordered a few of them as replacements from mouser, along with some of the tiny LEDS (removed a few as I thought that I may have installed backwards during initial build (I did not)).

Ok, so new MJE350's installed, checked out all of the LEDs, and wired it all up again.  I now have LED's lit for the A and B boards, but no LEDs lit on the large board.   Did a quick voltage test and I'm only seeing 3-5 volts on pins 1 & 2, so I just cut testing further short.

I can and have reverted the crack to stock and works fine, retested all voltages and they are right in manual spec.

Thoughts?  Might I have blown the other smaller transistors as well as those I plugged in backwards?

[Paul Birkeland]

Ok, so new MJE350's installed, checked out all of the LEDs, and wired it all up again.  I now have LED's lit for the A and B boards, but no LEDs lit on the large board.   Did a quick voltage test and I'm only seeing 3-5 volts on pins 1 & 2, so I just cut testing further short.

I can and have reverted the crack to stock and works fine, retested all voltages and they are right in manual spec.

Thoughts?  Might I have blown the other smaller transistors as well as those I plugged in backwards?

Pins 1 and 2 being terminals 1 and 2? 

Try the amp with just the 12AU7 (no 6080) and just the small boards installed.

-PB

[sadkins]

Sorry, yes terminal 1 and 2 I was referring to.

I tested without the 6080 installed and have results of the following -

- terminals 2 and 4 appear a bit high at 220v

- terminals 1 and 5 are at 80v.


Thanks for any help,

[Paul Birkeland]

Terminal 2, 4, B2, B5, and 13 are all wired together.

If you get different voltages at any of those terminals, you have a loose wire or funky connection.

[sadkins]

Nope all those are reading the same voltage.

[Paul Birkeland]

Does this happen immediately after turn on, or after a few minutes?

Did you use all of the hardware included to mount the TIP-50's? 

[sadkins]

right from the start.  I am using all of the hardware for the TIP50's with the exception of the clear thermal pads that sort of fell apart when putting together.  I had used a bit of heatsink compound paste in its place.  Would this cause a problem?

[Paul Birkeland]

Yes, that is absolutely your problem. 

[sadkins]

Ok, so its not actually supposed to contact the metal heatsink.  Is there anything I might be able to purchase locally in place of those brittle plastic pieces that came with the kit?

[sadkins]

I now have low volume on the left channel only, with some scratchy sounds also coming through.  Rechecked all solder joints.  Could I have possibly already damaged the transistors having them directly contacting the heatsink?

Amp was awesome prior to the attempted Speedball upgrade, struggling more than I'd have thought with this.

[Paul Birkeland]

You need TO-220 insulators.  The insulator is an electrical insulator to keep the metal tab of the TIP-50 from touching the heatsink.  The heatsink is grounded.  I made this choice because the Crack base is fairly compact, and it didn't seem tough to imagine fingers possibly making accidental contact with the heatsink accidentally.

You can purchase a pair of replacement heatsink kits from us by e-mailing replacementparts(at)bottlehead(dot)com.

You can just install the small boards to verify their functionality with the 12AU7.

If you continue to run the big PC board and 6080 without the insulators, you will continue to cause damage, and eventually you will need to replace the entire large PC board and its components.

-PB

[sadkins]

Thanks, will order some new insulator pads. 

I have ordered all replacement transistors from mouser to rebuild the boards again, if still no go after this will likely just scrap the speedball entirely and just settle on the already pretty great default crack sound (and come to live with my $150ish worth of failed speedball project parts.)

[Paul Birkeland]

It would be a good idea to start by verifying that the small PC boards work.  You can install them and use the 3K resistors, and the amp will be operational.

This will narrow down the issues to the big board only.

-PB

[sadkins]

I have reverted the amp several times and continues to work as stock.  I will try the small boards only with the resistors in place to see if I can rule those boards out for rebuilding.  Thanks,

[sadkins]

Ok, making some progress.  Removed large board.  Left the two small A & B boards and wired the 3k resistors back into place and amp appears to function normally. 

So at least now I can just focus on rebuilding the large board.  I have all the transistors coming to do a full rebuild and proper insulating kits for the TIP50's as well.

Thanks for the help.