LED's not lighting at all (resolved)

[ALphabloom]

Hi everyone,

Just built my first ever Crack. When doing the final testing of the amp, both LED's do not light up. The voltages are as follows

Incoming voltage: 245AC (AUS)
PT7 + PT9 = 6.0v
PT11 + PT12 =177.5v

Resistance check = Pass

Voltage DC:
T1: 147-8v
T2: 163v
T3: 0v
T4: 163v
T5: 147-8v
T6: 0v
T7: 146v
T8: 0v
T9: 146v
T10: 0v

NOTE: I have changed the pot to an alps RK27 100KAx2

Any help would be great, I really want the try this out!

 

[Deluk]

One LED doesn't appear to have a leg on. The other one isn't visible in the picture.

 

[ALphabloom]

so I just tried playing music on this, the left channel keeps getting crackly every so often before clearing up and repeating again, this is not effected by volume.

 

[ALphabloom]

my camera's is having a hard time focusing, but from what I can see, the LED's are connected

 

[Paul Birkeland]

Why would you try to use an amplifier that has not passed its voltage checks and is not operating?  You are taking a lot of unnecessary risks and learning absolutely nothing in the process.

The first thing to check is that the 12AU7 glows when the Crack is powered up. No glow=no conduction=no glowing LEDs.

 

[ALphabloom]

Why would you try to use an amplifier that has not passed its voltage checks and is not operating?  You are taking a lot of unnecessary risks and learning absolutely nothing in the process.

The first thing to check is that the 12AU7 glows when the Crack is powered up. No glow=no conduction=no glowing LEDs.

the 12AU7 glows

 

[ALphabloom]

Anyone have any ideas how to fix the issues?

 

[Doc B]

What's going on at A7 and A8? The image is too fuzzy to tell, but it looks like there might be some excess lead from one of those terminals very close to the other terminal. It also looks like the insulation of the red wire connected A7 might be interfering with the wire connection. A sharper photo could be very helpful.

 

[Paul Birkeland]

If the 12AU7 is glowing but not conducting, then the next thing to measure (very carefully) are the actual voltages at A2, A3, A7, and A8.

-PB

 

[ALphabloom]

Hi everyone,

Thanks for your suggestions, I fixed the problem by re flowing some solder and removing some solder (no more of that crackling on the left channel and LED's now glow), issue is there is noise (low constant hiss even without anything playing) even when the pot is turned all the way to the right channel then moves to the left channel the closer it gets to the other side of the pot.

 

[ALphabloom]

With a bit more tinkering, it seems the noise might be coming from the 220uf capacitors touching the wood, since every time I tap the amp onto the table, the noise on the left channel changes in loudness, sometimes becoming inaudible and other times you can hear it, is there any suggestions in regards to giving the cap and wood box more clearance or will putting electrical tape where the cap touches the wood solve the issue?

 

[Doc B]

Resolder the cap connections.

 

[Leland Hankins]

How about just bending the caps straight up so that they do not touch the base.

 

[Paul Birkeland]

How about just bending the caps straight up so that they do not touch the base.

That won't fix a flaky solder joint.

 

[Leland Hankins]

True, but it will get the cap away from the "wood" ("it seems the noise might be coming from the 220uf capacitors touching the wood"), the flaky solder joint is in your bailiwick.

 

[Paul Joppa]

The cap touching the wood is not itself a problem - but when it touches anything that moves ("when you tap the amp ...") the cap's solder connections will be stressed, which will usually expose a less-than-perfect solder joint.