[FIXED] terminal 7 is OL and OB on Speedball is OL. My bad....

[superdonkey]

Greetings, Bottleheads!

I have run into a problem, and could use some troubleshooting assistance.

My rig is a lightly modded Crack with Speedball add-on.

So, here's what I did:
Recently received a new power tube. Went to swap it in after a long session of cracking out, and I apparently mis-aligned the power tube!  When I powered the amp up, I heard a very loud buzzing static in one channel of my headphone.  Immediately powered it down & unplugged power cable.  Waited 10 minutes, removed the tube, but the plastic center guide pin snapped off inside the socket.  I carefully pushed the broken plastic guide pin out from below, then did a resistance check.  Terminal 7 and Terminal OB on big Speedball board now measure as OL.  The other terminals on the big Speedball board gave appropriate resistance values.  Every other resistance on the Crack gave appropriate resistance values.  I also tested the headphones (Sennheiser 650) on another device; they were undamaged.

As far as I can tell, I must have rotated the power tube 1 or 2 pins clockwise from the correct orientation. 

Question 1:  What are my next steps before attempting to power the Crack up again?  Any idea on what parts I need to test or will certainly need to replace?  I do have another power tube on hand to test things with. 

Question 2:  Also, the broken power tube has the end of a glass ampule/closure area of the vacuum tube inside the now-removed center guide pin.  The ampule does not look broken.  Is it possible that the tube is salvageable?  Is there any way to test it?  I do not have easy access to a tube tester.

Current installed mods are: Speedball kit, Alps Blue pot + hookup circuit board, Dayton 100uf 250v output caps, Mills 270 ohm resistor from terminals 15 to 21, and 3rd PS cap is tipped with a ClarityCap.

Any info or help would be greatly appreciated.

Thanks for your time,
Greg

[Paul Birkeland]

What resistance measurement do you get on OA on the big board? 

You'll probably need to power it up with no headphones and check the DC voltages to see what's going on. 

[Paul Joppa]

https://www.tubedepot.com/products/octal-tube-keyway-replacement?v=3898&utm_source=google&utm_medium=cpc&adpos=&scid=scplpSK-8KWY&sc_intid=SK-8KWY&gad_source=1&gclid=CjwKCAjw5PK_BhBBEiwAL7GTPUmlTOsaDgB2wYdVxggdBo39PeY1qI8f9J_b6Q466KEN1G88H2w28hoCREcQAvD_BwE

Just sayin'  :^)

[superdonkey]

First off, thank you both for the speedy responses today, and for being pillars of this community.  I have been lurking here since 2016 and have learned a lot from you two. 

@Paul Birkeland:  My DMM reads 08.45 m ohms resistance at terminal OA.  Please let me know if I should proceed with a live voltage check.

@Paul Joppa:  Thanks kindly.  I had no idea those existed! 

[Paul Birkeland]

8,450,000 Ohms and OL are about the same (OL is usually anything over 10,000,000 ohms).

Definitely do a voltage check.  Also look at the 100uF coupling caps to see if one got destroyed in the process, you'll see a bulged top if this happened, the voltage at either 7 or 9 will stay at 0V, and the power supply will start smoking if you have a dead power supply cap.

[superdonkey]

@Paul Birkeland: 

Thank you for the info and warning about smoking amp. 

Power supply caps looked fine.  Output caps looked fine.  The big film output cap on same side as terminal 7 (closest to headphone jack) had a very slight outward bulge on the top & bottom, in comparison to the big film output cap on the other side.  I would say it's maybe 1-2 mm wider at the center where the wire leads poke out.  Then again, it could have been like that from the beginning & I just didn't notice it.  None of them were definitely busted out like what happens with electrolytic caps.

Voltage test has been completed.  (Nothing started smoking, nor caught on fire.)  All LED's lit up.  All voltages were in range of the manual, for the Crack and both Speedball boards.  I did a second resistance test, and got the same results as what I originally posted.

What should I do next?

Thanks,
Greg

[Paul Birkeland]

If the voltages are OK, you can use the amp.  The film caps you put in will be pretty tough to kill, but it's always a good idea to double check.

[superdonkey]

If the voltages are OK, you can use the amp. 

Paul, thank you for the quick response. 

So just to be clear here:  Terminal 7 and Terminals OA & OB on big Speedball board still measure as OL.  It's still safe to use headphones?
edit: I tested out the amp with a sacrificial headset... I'm getting both channels to play. 

What's going on that terminal 7's resistance differs from terminal 9, yet it still plays fine?  Should I reflow the joints that are measuring incorrect resistance?

[Paul Birkeland]

Again, you are measuring 8 million Ohms on terminal 7 and over 10 million on terminal 9, these aren't really all that different.  It's important that you still see 0 ohms on 6 and 10 with no headphones plugged in, or about 2.5K with a 1/4" to 1/8" adapter plugged in.

[superdonkey]

Again, you are measuring 8 million Ohms on terminal 7 and over 10 million on terminal 9, these aren't really all that different.  It's important that you still see 0 ohms on 6 and 10 with no headphones plugged in, or about 2.5K with a 1/4" to 1/8" adapter plugged in.

Paul, thanks again for the info and for your patience with my questions.  I am not trying to be a pest, or question your judgement.  You obviously have lots more experience than I do.  This is my first electronics kit project, and I still have a lot to learn about circuits in general.  I have nobody local to help me, so researching & asking questions here on this forum is how I learn.  I was concerned that I had ruined my first serious electronics project, so I wanted to proceed with caution.

I was mainly concerned that my resistances for terminals 7 & 9 were either OL or in the millions, when the Crack manual states they should be at 2.9k ohms.  (Although, I'm guessing the 2.9k figure would change once the Speedball kit is added, but going OL seemed wrong to me, as it suggested a broken connection in the circuit.)  It did not make sense that the readings would be OL, considering that those wires carry audio signal through the output caps.  That's the reason why I asked again before plugging in headphones.  Upon repeated testing, terminals 7 & 9 read in millions of ohms, which makes a lot more sense to me than before. 

I do have one last question, if you have the time. 
You stated above that terminals 6 and 10 should read 0 ohms resistance with no headphone plugged in, and ~2.5k with  a 1/4" to 1/8" adapter plugged in.  I tested these conditions, and terminals 6 & 10 always measure at ~2.5k, regardless of whether a headphone adapter is plugged in or not.  Is this something to be concerned about? 

Thanks for your help with everything

Greg

[Paul Birkeland]

If you have the Crack 1.0, then 6 and 10 won't ever read 0.  We changed how the jack was wired in the revised amp and took advantage of the switching function of the jack.

[superdonkey]

Paul,

I am assuming it's a 1.0.  The kit was purchased in early 2017, and my manual is from 2013.  Not sure when the version changed happen, but 1.1 is not mentioned anywhere in my manual.  I suppose that would explain things   Thank you for clearing that up!

This is my final question, I promise!  The power transformer on my amp is running hotter than before.  (Before what?  Definitely the "broken keyway incident", and perhaps even before installing the Speedball upgrade.)  I ran it for about 2.5 hours tonight, and the outside of the power transformer had gotten quite hot.  I could only touch my fingertip to the side for perhaps 5-6 seconds before needing to pull away.  Is this (admittedly ballpark) temp normal, or is this something to be concerned about? 

Thanks again,
Greg

[Paul Birkeland]

If all your DC voltages are normal, then your power transformer is operating properly.

[superdonkey]

Paul,

Thanks for letting me know, and walking me through the troubleshooting process.  I was worried that I had somehow damaged the amplifier.  I really appreciate all the help.

Best,
Greg