Help to troubleshoot my Crack (RESOLVED :)

[kgoss]

Just a troubleshooting suggestion, but the fact that you are able to repeatedly create these symptoms makes a big difference.  Next time you get a chance to work on your amp run it upside down in the base, or on books, etc.  The key is to have easy access to the bottom so you can perform a complete voltage check while the problem is occurring. Post any voltages here that are out of spec and someone a lot more knowledgable than me will help you sort it out.  If the voltages are all good when the sound stops then I'd look long and hard at the signal path wiring.  Paul B can help you trace that by taking measurements with your meter while playing a test tone.

And if you can't reproduce the problem with the amp upside down you'll just have to build a clear cover and run it that way from now on!  Just kidding.  If you can't reproduce the problem with it upside down that provides clues too.  That would send me looking for a mechanical issue caused by gravity when the amp is in the base.

Don't get discouraged. PB and the rest of the BH team are great at solving these tough issues and won't give up until your amp is fixed.

 

[ju29]

Thanks for your replies. Offer very appreciated Richard, thanks. I stay in Hull close to Ottawa. No trip scheduled to Mtl soon but if my plan changes (and if have still have the pb at this time) I'll let you know... The 3K resistors measurements are ok (and the others resistors as well). Well noted also about the two others pairs of eyes around me..

Ken I did that already. I've posted my voltage measurements when the pb occur : every measurements are perfects when both sides work in my headphone. When the left side stops after a couple of minutes, B6 and T9 are down to 0 and almost all others voltage measurements increase slightly (see my first message for the exacts measures). I've also made once a resistance check when the issue occur I got 0.08 at T6 and T10 instead of 2.9K but I didn't repeated the measurement. So that is based on a one time measurement... Also the RCA jack (white) seemed to be at 0 or at least I wasn't able to measure anything (the red one was at 98). And the pb occur when the crack is on both sides (so no need to get a clear clover...


About the soldering I made sure for each of them that there were a good/large contact between the wire and the terminals. When I destructed the crack I removed the solder/used sandpaper and used a sharp knife to scratch a little bit the terminals to make sure there would be a good contact. Then I resoldered as I said before. Since I do as Grainger kindly advised me in his message, last paragraph.


About the BH team, yes I hope so.. Without any news from them since a couple of days I guess I have to continue to use my solder and check and recheck my solders..

 

[Paul Birkeland]

Once the problem occurs, can you confirm that your voltages on terminals 1-5 are still correct? (You are right, they will pop up a bit)

Once you have the problem and are able to measure your voltages, try measuring the voltages on B1-B3.

In particular, I'd like to see if B1 and terminal 1 have different voltages when the problem occurs. 

 

 

[ju29]

Hi Paul, thanks for your reply.

From my notes :
Terminal 1 : 83 before the pb // then 89 when the pb occur
Terminal 2 : 173 before the pb // then 198 when the pb occur
Terminal 3 : 0 before the pb // then 0 when the pb occur
Terminal 4 : 173 before the pb // then 197 when the pb occur
Terminal 5 : 80 before the pb // then 88 when the pb occur

B1 : 83 before the pb // then 89 when the pb occur
B2 : 172 before the pb // then 194 when the pb occur
B3 : not quite sure one this one // then 121 when the pb occur

I have to leave in a couple of minutes. I will do an other measurements in a few hours when I'll be back. I measured many time and every time the result was the same result. But again, I'll do an other test just to be 100% sure.

Thanks !

 

[Paul Birkeland]

Oops, I got mixed up (thought 7 was the issue).

Try the same test on B4, B5, B6 and terminals 5 and 9.

 

[ju29]

Since the left hear doesn't work for the first 10 to 15 seconds I thought that would be a good idea to get the measurement as well for this short time. So I plugged/unplugged a couple of time, waiting a minute between two measures. 10 seconds is a short time and and wanted to get accurate measures.


So here are my fresh voltage measurements I've just made :

B4 : the 10 first seconds 89 // then 79 for 3 to 6 minutes // then back to 89
B5 : the 10 first seconds 238 (!!!) // then 170 for 3 to 6  minutes // then 194
B6 : the 10 first seconds 0 // then 103 for 3 to 6  minutes // then back to 0
T5 : the 10 first seconds 230 (!!!) // then 79 for 3 to 6 minutes // then 89
T9 : the 10 first seconds 0 // then 103 for 3 to 6 minutes // then back to 0



Others measures (just in case) :
B1 : the 10 first seconds (?) // then 83 for 3 to 6 minutes // then 89
B2 : the 10 first  seconds (?) // then 170 for 3 to 6 minutes // then 194
B3 : the 10 first seconds (?) // then 107 for 3 to 6 minutes // then 120
B7 : the 10 first seconds (?) // then 0 for 3 to 6 minutes // then 0
B8 : the 10 first seconds (?) // then 0 for 3 to 6 minutes // then 0

T1 : the 10 first seconds (?) // then 83 for 3 to 6 minutes // then 89/b]
T2 : the 10 first seconds (?) // then 170 for 3 to 6 minutes // then 194
T3 : the 10 first seconds (?) // then 0 for 3 to 6 minutes // then 0
T4 : the 10 first seconds (?) // then 170 for 3 to 6 minutes // then 194
T6 : the 10 first seconds (?) // then 79 for 3 to 6 minutes // then 89
T7 : the 10 first seconds (?) // then 107 for 3 to 6 minutes // then 120
T8 : the 10 first seconds (?) // then 0 for 3 to 6 minutes // then 0
T10 : the 10 first seconds (?) // then 0 for 3 to 6 minutes // then 0




I wait for you feed back. Thanks for your help !



PS: I may be completely wrong but I have the impression to hear something (in the bulb I think) when the measures changes.

PS2: It will work !

 

[Paul Birkeland]

PS2: It will work !

Yeah, we'll get you there.

Ok, I have one odd suggestion for you that will about wrap up the diagnosis.  Remove the wire at B3 and remove the wire at B6 (just at the octal socket end, you can leave each free end poking up and hanging in the air).

Wire a temporary jumper from terminal 7 to B6 and a temporary jumper from terminal 9 to B3. 

Now remeasure and see if the 0V reading has moved terminals or remains where it was.

-PB

 

[ju29]

Argh, I was so proud of this solders. B3 and B6 were my favorites !!

Just kidding..


Here are the measures :

B4 : the 10 first seconds 0 // then 0 for 8 minutes (didn't wait any further).
B5 : the 10 first seconds 238 // then 194 for 8 minutes (didn't wait any further).
B6 : 0 // then grow slowly during the 10 seconds to stop at 119. Didn't change after for 8 minutes (didn't wait any further).
T5 : the 10 first seconds 230 // then 89 for 8 minutes (didn't wait any further).
T9 : the 10 first seconds 0 // then still 0 for 8 minutes (didn't wait any further).


Fingers crossed..

 

[Paul Birkeland]

If B6 never fell back to 0V, then we can conclude that the 6080 is working properly, the socket is working properly, the solder joint at B5 is good, the solder joint at B4 is good (despite your 0V reading at B4, which isn't possible based on all other information), and that the path from ground, through the 3K resistor, and to the terminal strip is working on the headphone jack side of the amp, but not the volume pot side of the amp.  This also confirms that the 12AU7 is doing what it needs to do to bias both halves of the 6080 properly. 

This is absolutely a flaky connection, likely at terminal 3 or terminal 9.

It might help to triple check the resistance between terminal 3 and terminal 9, to make sure that terminals 9 and 10 don't have any debris between them that's conducting, etc.

 

[ju29]

Hi I've posted the wrong measures...
(I removed B4 instead of B3 so the former measures are not what you asked me...)

I post the right one in few minutes....

 

[ju29]

Ok removed B3 and B6 and put B3 to T9 and B6 to T7

I was able to measure only B4 (230) and B5 (238) then few seconds after there was some smoke/smell.
I think it's the resistor of 22.1K (the one the closest to the headphone plug) that started to burn...

I unplugged as soon as I realized there were some smoke. It stayed plugged for maximum 5 seconds.

 

[Paul Birkeland]

Ok removed B3 and B6 and put B3 to T9 and B6 to T7

I was able to measure only B4 (230) and B5 (238) then few seconds after there was some smoke/smell.
I think it's the resistor of 22.1K (the one the closest to the headphone plug) that started to burn...

You must've wired something to T6 or T10 by mistake.

 

[ju29]

You're right (of course you are ! the alligator clip from T9 touched T10.. Argh, haven't seen it...
Measures in couple of minutes...

 

[ju29]

B4 : the 10 first seconds 230 // then 80 for 3 to 6 minutes // then 89
B5 : the 10 first seconds 238 // then 170 for 3 to 6  minutes // then 194
B6 : the 10 first seconds 0 // then 103 for 3 to 6  minutes // then back to 0
T5 : the 10 first seconds 230 // then 80 for 3 to 6 minutes // then 89
T9 : the 10 first seconds 0 increase slowly to 103 // so 107 for 3 to 6 minutes // then to 119

 

[Paul Birkeland]

We will mail you a replacement 6080.  The intermittent nature may suggest that the tube is actually not properly soldered itself.  If possible, please update your forum signature with your name (first initial and last name is sufficient) so that I can get this in the mail tomorrow for you.

-PB

 

[ju29]

Ok, thanks Paul for the follow up. Appreciated. Let me know when you'll identify me with my signature. Then I'll change it after.

About the results/measures I suppose you're 100% sure of your verdict (for me the numbers I give you are just like chinese...). But if you need more tests/measurements to confirm it, just let me know and I'll proceed...

Have a good day/evening

 

[ju29]

Little update of my situation...

I was to impatient to know if the tube was the issue, I ordered last week a cheap 6080 from Tubedepot.

The 6080 received 2 days later, I installed it and since... my Crack works perfectly.
So there it was... the 6080 tube...

THANKS Paul and everyone for the help to troubleshoot my Crack. The good point is that I practiced a lot (I mean a lot !) my soldering skills. I think that it helped me during the speedball upgrade I've just done tonight. So nothing happens for nothing... I've been listening for music for something like an hour tonight with the speedball upgrade and I enjoy every seconds of it.


Next step, try few others 12AU7-like tubes. But no rush, I just need to enjoy the music now... 


Have a good night (/day)