Help with voltage [resolved]

[kill_surf_city]

Both tubes light up completely and one LED lights up (A8).

Here’s my readings:

1. 94.5
2. 183.3
3. 0.0
4. -00.1
5. -00.1
6. Starts at 95 then gradually drops
7. 144.7
8. 0.0
9. 67.7
10. 93 then gradually drops

 

[Paul Birkeland]

Terminals 2 and 4 are wired together with a jumper wire.  I would guess that yours is missing or not well soldered.

 

[kill_surf_city]

Terminals 2 and 4 are wired together with a jumper wire.  I would guess that yours is missing or not well soldered.

Thank you, Paul. I’ll check it out.

 

[kill_surf_city]

Terminals 2 and 4 are wired together with a jumper wire.  I would guess that yours is missing or not well soldered.

Yep, turns out I had missed that step completely. Just put it in and rechecked the voltage. Only terminals that are out of range are 6 and 10. Both should be zero but 6 floats around 100 then gradually starts to drop. 10 starts at 101 then floats between 99.3-99.4. Any idea what the problem is here?

Edit: google search came up with my headphone jack being miswired. Fixed it but now my voltages are all too low.

 

[Paul Birkeland]

Edit: google search came up with my headphone jack being miswired. Fixed it but now my voltages are all too low.

What was miswired?  What did you change?

"Too low" is not a number and doesn't tell me much about what's going on.

Please post build photos at your earliest convenience.

 

[kill_surf_city]

What was miswired?  What did you change?

"Too low" is not a number and doesn't tell me much about what's going on.

Please post build photos at your earliest convenience.

The black wire that goes from 3L to the headphone jack wasn’t wired all the way up, so I removed the wire and replaced it correctly. Now the one LED that was turning on, turns on initially then goes out. Here’s my readings now.

1. 45
2. 72.6
3. 0
4. 73.4
5. 17.1
6. 0
7. 49.9
8. 0
9. 14.3
10. 0

 

[Deke609]

Not sure if this is related to the problems you're having, but you have some leads that need trimming, particularly the one circled in the attached. It looks like it might be creating a short to chassis ground.

cheers, Derek

 

[kill_surf_city]

Not sure if this is related to the problems you're having, but you have some leads that need trimming, particularly the one circled in the attached. It looks like it might be creating a short to chassis ground.

cheers, Derek

Thanks. Also just realized the right blue capacitor is getting warm but the left one is not. Hmmm.

 

[Paul Birkeland]

A blue cap that gets hot could be in backwards, but I can't see that from your photos.

 

[kill_surf_city]

A blue cap that gets hot could be in backwards, but I can't see that from your photos.

Oh shit you’re right! I feel so dumb. Thanks Paul. I’ll turn it around and report back soon

 

[Deke609]

From the photo it looks like the top of the cap is already bulging. PB can tell you if it's still usable.

 

[kill_surf_city]

Ok I got both the caps in the right orientation now. Here’s my new readings. Neither LEDs are turning on.

1. 134.2
2. 169.2
3. 0
4. 169
5. 124
6. 0
7. 140.7
8. 0
9. 135.2
10. 0

 

[kill_surf_city]

From the photo it looks like the top of the cap is already bulging. PB can tell you if it's still usable.

I think the cap is blown. I re-did the voltage checks and the numbers are all in range except for terminals 5 and 7 which I’m pretty sure is the left channel. So I thought what the hell, and decided to plug it in and see how it sounds. Right channel is absolutely silent and when I played music it sounds incredible - like absolutely perfect.  The left channel however, barely any music came through if any at all and it’s mainly a loud hiss with some crackles here and there. Does that sound like the cap needs replaced? If so how do I go about ordering a new one?

 

[Jameson]

You really ought not try to listen to the amp with the voltages out of spec.

Mouser will carry those capacitors, as will digikey

 

[kill_surf_city]

You really ought not try to listen to the amp with the voltages out of spec.

Mouser will carry those capacitors, as will digikey

Thank you. Does what I’m describing sound like a blown capacitor?

 

[kill_surf_city]

A blue cap that gets hot could be in backwards, but I can't see that from your photos.

Caps are now put in properly.
Final readings before I do anything else

1.  84.6
2.  174.3
3. 0
4.  174.3
5.  116.8 *
6. 0
7.  107.6
8. 0
9. 130.3 *
10. 0

5 and 9 are out of range. Neither LED lights up.

 

[Deke609]

I think you should wait for PB's input before powering the amp again.

But there is one thing I would suggest doing in the interim . See circled area in the attached pic: the black wire has too much exposed wire and looks like it might be touching (or might end up touching) the lead of the diode below it. If that happens, I think you'll have a short circuit every half cycle that will draw a ton more current than the transformer and diodes are meant to handle. I suggest reheating the joint and pulling the black wire further into the solder lug so that the bare wire and the diode lead no longer overlap.

I've also indicated with arrows what look to me like signs that the first 270 ohm resistor has been overheated - this is really just to bring it to PB's attention. I'm not sure if has been overheated, or even if it has, whether this is a problem. PB will let you know.

cheers, Derek

 

[kill_surf_city]

I think you should wait for PB's input before powering the amp again.

But there is one thing I would suggest doing in the interim . See circled area in the attached pic: the black wire has too much exposed wire and looks like it might be touching (or might end up touching) the lead of the diode below it. If that happens, I think you'll have a short circuit every half cycle that will draw a ton more current than the transformer and diodes are meant to handle. I suggest reheating the joint and pulling the black wire further into the solder lug so that the bare wire and the diode lead no longer overlap.

I've also indicated with arrows what look to me like signs that the first 270 ohm resistor has been overheated - this is really just to bring it to PB's attention. I'm not sure if has been overheated, or even if it has, whether this is a problem. PB will let you know.

cheers, Derek

Got it. Thanks!

Edit: there was actually a pretty good amount of space between the wire and the diode but I pulled the black shielding further over anyway.

 

[Paul Birkeland]

Do both halves of the 12AU7 still glow?  Your voltages tell me that one half is not conducting.

Do not listen to an amp that hasn't passed its voltage checks.  Those tell you whether or not the amp is working properly, and an amp that isn't working properly can destroy headphones.  (In fact having the 100uF cap in backwards will melt one headphone driver if you tried to listen to the amp like that, if you put a bulged cap back in and attempted to listen to the amp, you may have already caused some damage)

 

[kill_surf_city]

Do both halves of the 12AU7 still glow?  Your voltages tell me that one half is not conducting.

Do not listen to an amp that hasn't passed its voltage checks.  Those tell you whether or not the amp is working properly, and an amp that isn't working properly can destroy headphones.  (In fact having the 100uF cap in backwards will melt one headphone driver if you tried to listen to the amp like that, if you put a bulged cap back in and attempted to listen to the amp, you may have already caused some damage)

Yep. Both sides of the 12AU7 glow.