Speedball Upgrade Smoking!

[Paul Birkeland]

I don't know how a defective transformer would cause problems with the resistance readings.  I haven't run into that before...

If terminal 3 is 0 ohms and you have 3K resistors between 3 and 7 as well as 3 and 9, then you should see about 3K at 7 and 9.  Not seeing that there would have me asking to see some fresh build photos.

[iskess]

Alright, after testing I discovered that the 3kΩ resistors between 3 --> 7 and 3 --> 9 weren't supporting continuity, as — in the process of initially removing them for installation of the Speedball — I'd practically severed their leads. Needless to say, I've now replaced both 3kΩ resistors altogether. After doing so, I went about taking another round of resistance checks, and this time discovered only a few erroneous readings. See below:

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1 - 13.14MΩ
2 - fluctuating
3 - 0Ω
4 - fluctuating
5 - 13.17MΩ
6 - 2.49kΩ <--- outright bad
7 - 2.96kΩ
8 - 0Ω
9 - 2.95kΩ
10 - 2.48kΩ<--- outright bad
 
12 - 0Ω
13 - fluctuating
14 - 0Ω
 
20 - 0Ω
22 - 5-9MΩ <--- outright bad

B3 - 2.96kΩ
B6 - 2.95kΩ

Center pins of RCA jacks - both within acceptable range (red and black were 100kΩ & 95kΩ respectively)

Ground tab of RCA jacks - 0.9Ω <--- seems a little high but still acceptable
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(While considering the readings above do consider that the small speedball circuit board is still installed. Not sure if that changes anything but thought I'd mention it.)

I'm happy to be making progress. Any advice on what might be causing the erroneous measurements at terminals 6, 10, and 22?
Thank you so much for your help,
Jordan Bouret

[Paul Birkeland]

Do you have a 1/4" to 1/8" adapter plugged into your amp by chance?

[iskess]

Oh my word, I do. Has that affected measurements? I hadn't been aware it could.

[Paul Birkeland]

It will make terminals 6 and 10 measure 2.49K rather than 0.

[iskess]

Any related explanation for that strange resistance reading on terminal 22?

[Paul Birkeland]

Tighten that transformer screw.  That resistance won't cause operational issues with the amp.

[iskess]

Alright, the crack passed all resistance checks, so I plugged the tubes in and went about conducting voltage tests.

Here are the results for terminals 1-10:
1 - 72.5V
2 - 164V
3 - 0V
4 - 165V
5 -  157V <--- too high

6 - 0V
7 - 97V
8 - 0V
9 - 155V <--- too high
10 - 0V

Also do note that after testing the 12AU7 tube was warm but not hot to the touch. I could still very comfortably touch it whereas the 6080 tube was much hotter.

Any insights on what might be causing such high voltages at terminals 5 & 9? Thanks a bunch!

[Paul Birkeland]

The center leg of the MJE350 feeding terminal 5 may not be adequately soldered.

If this is the Speedball 1.1, the instructions call for checking the voltage on the small board before proceeding with the rest of the upgrade.  Did your amp pass those checks?

[iskess]

I'm almost positive the small board passed those voltage checks, yes. Also, the center leg of the MJE350 looks pretty well-soldered to me (see photo attached).

I'll can try to rerun the Speedball 1.1 voltage checks, and get back to you.

[Paul Birkeland]

I would apply a lot more heat to that middle joint.

[iskess]

After a very long hiatus (I really needed to focus on school for a while), I've decided to resume the repair process and finally get my Crack up and running again.

My Crack passed all resistance checks last year, but I wanted to test again before applying voltage, just to make sure nothing had loosened or corroded over time.

This time around, all terminals gave proper resistance readings EXCEPT for Terminal 6, which gave a reading of 2.48kΩ. Terminal 10 did read 0.5Ω, not exactly 0, but I think that's okay.

Note that there were no tubes installed and no aux adapter plugged in, and the power switch was set to off (not that I suspect it makes any difference). Also, please recall that I have the small Speedball board installed, but not the large Speedball board... instead I've reinstalled both 3kΩ resistors.

What do you suspect is the issue here?
Thank you for your time
Jordan

[Paul Birkeland]

The 1/4" headphone jack wiring isn't properly connected or soldered if you have that issue.

[iskess]

Hmmm, the 1/4" jack wiring looks pretty good to me (see photo attached).

Interestingly, I did just notice that one of the LEDs on the bottom of the smaller tube socket has a severed lead (circled in blue in photos attached). It's the LED nearest the very bottom edge of the amp. Earlier in this thread, I was having problems with the smaller tube during voltage testing (please scroll up and see my post from June 1st). Could this LED be the issue?

Thanks

[Paul Birkeland]

The outer lower and outer middle lugs on your headphone jack don't look like they have been adequately heated for the solder to flow out.

Yes, you'll need a new LED on the socket where that one is broken.