Irregular Crack Speedball Voltage Measurement at Terminal OB

[iskess]

After using (and loving) my Bottlehead Crack for a year with HD 650s, I decided on the Speedball upgrade.
The stock Crack would occasionally begin making “dying squirrel” noises which could easily be remedied by quickly turning it off and on again. I’ve always assumed this is just a tube irregularity but thought I’d mention it here in case it serves as a clue.

Anyhow, here’s the actual subject of this post:

After wiring, soldering, and attaching the Speedball’s “small circuit board” to my Crack, I went ahead with the voltage test. The reading for every terminal fell within an acceptable voltage range with the exception of terminal OB, which measured 10v (it should be 60-90v). The manual’s included troubleshooting flowchart only contains OA/OB specific solutions for readings of 0v or >110v, and are thus not applicable to my particular problem. In case you were wondering, all four LEDs on the Speedball’s “small circuit board” light up with power applied to the amp, and the Crack’s fuse is not blown.

I find it very important to note that, on account of this being my first small-scale soldering project (the stock Crack required much less intricate soldering), I found it incredibly difficult to solder the center leg of each MJE-350 transistor. I had to re-solder each center leg around 6-8 times, and probably held the iron on for far too long each time, as the entire MJE-350 would always be too hot to touch afterwards. My theory is that I overheated and irreparably damaged the MJE-350 responsible for the OB terminal. If this is indeed the case, my stupidity doesn’t seem to have affected the other MJE-350, because the OA terminal is giving acceptable voltage measurements.

I’ve ordered some new MJE-350 transistors on eBay and am hoping that my theory is correct. If I did indeed fry one of the MJE-350s, I’m considering also replacing the other (functional) one just as a precaution, considering that I did subject them both to similar high-heat torture.

Below is some additional information which may serve as helpful in the pursuit of a solution to my problem.
While conducting the voltage tests, I noticed two irregularities:

1). The 6080 tube does not glow or become warm with power applied to the amplifier, while the 12au7 does. This was obviously not a problem before, as I’d been using the amplifier frequently up until I began the Speedball upgrade.

2). As you probably already know, the 9-pin socket (into which the 12au7 tube is plugged) contains two LEDs. When power is applied to the amplifier, only one of said LEDs lights up (while the other does not whatsoever). I’m not sure whether or not this was a problem before I began the Speedball upgrade, but I really think I would’ve noticed this upon initially building the stock Crack one year ago.

If anybody needs photos, please don't hesitate to let me know.

If you’ve read this monstrosity of a post up until now, I commend you. What an incredible community this is!
Thank you so so much.

Jordan B.
Amateur Audiophile

[Paul Birkeland]

Do not remove and replace the MJE350 transistors.  There isn't any indication that this is an issue.

I would post some build photos so we can look at what's going on. 

The noise you heard in the original build may well indicate a problematic solder joint.

The 6080 glows from the green twisted pair of wires going to pins 7 and 8 of the 8 pin socket.  If the 6080 isn't glowing, this wiring may be loose, the tube may be inserted improperly in the socket, or there may be an issue with the tube itself.

Your 10V of voltage coming out of the Speedball board and the dark LED, and the 6080 not glowing could all be explained by the 6080 being plugged in with the base key in the wrong position.  This mistake could short one output of the small Speedball board to the 3K cathode resistor.  The 3000 ohm cathode resistor with 3mA across it would show about 9V on the output terminal of the C4S, which is what you're observing.