New build same issues

[Knightstick]

Hello, I just got done rebuilding my crack with the same problems I previously had. It shuts off when it starts to get hot. I went over my work about 3 or 4 times when I was building it. I  checked each solder joint multiple times. I did get a reading that was somewhat strange at terminal #5. It was a resistance check and it was changing but it didn't jump all around like the others. It only climbed and kept climbing so I thought it was okay,  as it was changing. I did my voltage checks and everything was right on. The only thing I can imagine is maybe I over soldered. Some of the joints had quite a bit but they were shiny as foil so I figured it was good. Thanks in advance for any comments.

 

[Paul Birkeland]

Hello, I just got done rebuilding my crack with the same problems I previously had. It shuts off when it starts to get hot.

You need to put numbers on this.  What are the voltages at terminals 1-10 when the Crack shuts off?

 

[Knightstick]

You need to put numbers on this.  What are the voltages at terminals 1-10 when the Crack shuts off?

HI Paul, I took the readings. Terminal 1. .91 mv 2. .92 mv 3..2 mv 4. .92 mv 5..91 mv 6. .6 mv 7. .6 mv 9. .4 mv 10. .5 mv I also took readings at 13. Which was 7.2 v,  and 15 which was 9 v. I don't know if the last 2 are relevant. Thanks for all the assistance.

 

[Paul Birkeland]

How about 15 and 21?

Do the tubes continue to glow once this happens?

 

[Knightstick]

How about 15 and 21?

Do the tubes continue to glow once this happens?

The readings are terminal 15. 9 v and 21. 215 v and the tubes go out.

 

[Paul Birkeland]

15 and 21 are connected by a 270 ohm resistor.  If you had 9V on one end and 215V on the other, that would be 700+mA of current drawn across the resistor, which would be 157W of dissipation and more than enough to blow the fuse instantly. 

Consequently one end of that resistor is not well connected, or the resistor itself is damaged. 

 

[Knightstick]

@Paul I think I gave you erroneous readings yesterday. I reported the voltage at 15 to be 9 v. I had a call and measured it about 15 min later duhhh. I apologize. So the actual measurements at failure are 15.193 v and 21. 215 v. I went ahead and reflowed the joints but it failed afterwards so I don't think that's the problem.
Adam

 

[Paul Birkeland]

Again, these two terminals are connected by a resistor.  If the resistor is connected and you have those voltages, the resistor would burn up and fall apart into white powdery dust.  Since that hasn't happened, either one end of the resistor isn't well connected, or the resistor itself needs to be replaced.

Feel free to post photos of that area if you'd like us to double check.

 

[Knightstick]

Just to make sure. I place the negative lead on terminal 12 correct? Thanks in advance.

 

[Paul Birkeland]

Yes.

 

[Knightstick]

Thank you. Now I think I've found my issue.. I had the amp on a table next to my couch in a corner, and I believe I may have been starving it of air as it also sat lower than the couch. Could this be causing the problems I described? I re-soldered it again and it seems to be playing well in its more ventilated location. I've been jamming on it for almost 3 hours...I'm hoping this was the problem. Not 100% though.

 

[Paul Birkeland]

I don't seem to be communicating what's going on adequately well.  There are two possibilities for what's going on with your amp:

#1 - one end of the 270 ohm resistor that goes between 15 and 21 is not well soldered.
#2 - the 270 ohm resistor is damaged.

It is entirely possible that you've fixed your amp by resoldering each end of said resistor, but lack of ventilation will not cause the problems you're describing.