Made a big mistake with the main power supply :'(

[Doc B.]

Now measure the resistance from pin 4 to pin 5 on the 12AU7 tube. You should get a fairly low resistance reading. If it reads open the heater in the tube is blown.

[fissure]

Now measure the resistance from pin 4 to pin 5 on the 12AU7 tube. You should get a fairly low resistance reading. If it reads open the heater in the tube is blown.

Hi Doc, so i have read the resistance through all ranges and only get a 1(open) between pin 4 and 5 on the 12AU7 tube. So i guess it is broken? No idea how i managed to brake it though :/
So how do i go about to get a new one now?

Thanks for the help !

Edit: Is there any way to see if its broken visually? Cant see anything loose or that looks broken?

[Doc B.]

There is usually no way to see the broken heater wire in an indirectly heated tube like the 12AU7. An email to [email protected] will get a new tube on the way to you.

[fissure]

There is usually no way to see the broken heater wire in an indirectly heated tube like the 12AU7. An email to [email protected] will get a new tube on the way to you.

So i got a replacement tube locally where i live and plugged it in. This time it lit up fine and the two leds in the socket was working now as well so the tube must have been broken like you said. Everything checked out fine so i went ahead and installed the speedball upgrade but now i have a new issue. I have to high voltages on the right audio channel (i think it is the right one).
The leds on the right PCB is working as they should and terminals 4 and 5 have the correct voltages. But the left PCB is not working as it should, only one LED is emitting light (the right one on the left PCB, looking at it installed) and much weaker than the LEDs on the right PCB so i removed the LED and checked it with the diode tester on my multimeter (or whatever it is called) and i could not get it to light up. The other one i removed as well and tested with the multimeter but that one worked. So could it be a broken LED? I tested them all before installing and they all worked so it must have happened after soldering (can they be damaged from to much heat?). And can a damaged LED result in the weird voltages i am getting?

I also noticed when measuring that both the 150V tabs on the transformer now only delivers 70V. Is this normal?


1 75 - 153
2 170 - 159
3 0 - 0
4 170 - 160
5 75 -82
6 0 - 0
7 100 - 150
8 0 - 0
9 100 - 104
10 0 - 0
11 0 - 0
12 0 - 0
13 170 - 158
14 0 - 0
15 185 - 184
19 0 - 70
20 206 - 0 (should this be 21?) got 203VDC on 21 anways but 0 on 20
A1 75 - 81
A2 0 - 0
A3 1.56 - 1,53
A4 0 - 0
A5 0 - 0
A6 75 - 150
A7 0 - 0
A8 1.56 - 1,53
A9 0 - 0
B1 75 - 150
B2 170 - 160
B3 100 - 150
B4 75 - 81
B5 170 - 158
B6 100 - 104
B7 0 - 0
B8 0 - 0

Regards //John

[Paul Birkeland]

The LED was probably OK until it was removed. Unless an LED is visibly broken, we don't advocate removing it.

The issue you describe is likely either a bad solder joint on the center leg of the MJE350 or the wrong resistor installed at R1.

If both LED's on the nine pin socket light, I would think the wrong resistor to be more likely.

[fissure]

The LED was probably OK until it was removed. Unless an LED is visibly broken, we don't advocate removing it.

The issue you describe is likely either a bad solder joint on the center leg of the MJE350 or the wrong resistor installed at R1.

If both LED's on the nine pin socket light, I would think the wrong resistor to be more likely.

Hi again blackplate, was gonna check it this morning but when i turned it on this morning there was a nice loud crack (pun intended) coming from the powersupply and our main circuit breaker in our apartment released. Unplugged the crack and switched the power back on. Flipped it over and shook it and a tiny piece of solder fell out, this probably was the culprit of the short and i plugged it in again and turned it on. Now all leds are dead but both tubes are glowing. Only getting 6VDC on T1/5 and 225VDC pretty much everywhere else. Including the metal base plate?! So i figured that i unplug it again before i get myself killed
Anyways had to go to work so did not have any more time to work with it. My guess is that something have shorted, thing is how do i find it without tearing the whole thing down again.

Edit: Looks like it shorted between the main AC tab on the transformer and the 270 ohm resistor above. Measured it and it gave 265ohm back.

[fissure]

Ah man forum seems to have been rolled back My last two posts are gone.

Anyway to sum it all up.

I have removed the large PCB from the speedball upgrade. And tested with the 6080 removed.
T1 - 75V
T2 - 206V
T4 - 206V
T5 - 195V

Is my new tube broken as well? It seems like the second triode does not draw any power (if this is how it works?)
The two smaller PCBs was removed and resoldered and still the same issue. I switched the boards positions and the problem moved from T1 to T5 instead. Which leads me to belive the issue is with that PCB or an component on it.
The center leg on the MJE350 gives my 195V on the "broken" side and 75V on the left side if that is of any importance.

[Paul Birkeland]

The two smaller PCBs was removed and resoldered and still the same issue. I switched the boards positions and the problem moved from T1 to T5 instead. Which leads me to belive the issue is with that PCB or an component on it.
The center leg on the MJE350 gives my 195V on the "broken" side and 75V on the left side if that is of any importance.

Yeah, there's an issue with your smaller PC board.  That kind of voltage on the center leg of the MJE350 is nearly always a bad solder joint on the board (or potentially you have a 2N2222A on that board).

Sorry about the forum posts, we are wrapping up some website work. 

-PB

[fissure]

Have resoldered the MJE350 several times without result but will try again. I double checked the two small PCBs and both have the 2907A.


Edit: Resoldered 3 times now and it still does not work.
When the 12AU7 lights up i notice that both of the square metal parts emit light from the top so the heating seem to be working.
But i also noticed two blue glowing things on one side of the tube that seemed to be coming from triode 2 in the tube. But i can not see any such thing on the other side. Just a side note, note sure it is of any importance.

[Paul Birkeland]

What's important is that the voltage issue follows one of the boards. 

We can send you a replacement board, transistors, and resistors if you like.

-PB

[fissure]

What's important is that the voltage issue follows one of the boards. 

We can send you a replacement board, transistors, and resistors if you like.

-PB

Thanks! But i have ordered replacement parts today for one board from Elfa here in Sweden so i will have the parts on monday don't have the patience to wait +1 week ;P was not more than 10$ anyways. If the PCB itself is faulty i might have to get a replacement but if that's the case i will be in touch, or i might just use a lab board for it.

[fissure]

Ok so i received some replacement leds a couple of days ago. Replaced the Leds on one of the small boards. Hooked it up and plugged in the power. Now i have 80V on T1/T5 and 205V on T2/T4 so it appears to have been faulty leds that were the problem there (though no visual damage to them).
So i soldered back the big PCB again and hooked it up. Plugged in the Crack again and all leds turned on nice, was gonna measure but then i heard a whizzing sound for a couple of seconds and then a small pop. Turned it of as fast as i could and saw on the big board that the small 31,6kohm resistor had popped and also one of the leds on the board (was visually broken, cracked in half).
Will have to replace the broken components and double check my wiring this time. Any ideas what could have caused this?

[Paul Birkeland]

There is probably a solder bridge between two solder joints on the big PC board.

[fissure]

So just an update on the build. Got some pieces today that i switched (the popped resistor among them) and soldered it back together. Noticed that when i popped the resistor on the big PCB i probably had switched the place of two of the black cables (ooops).
Anyway it is all together now and there is sound !
Sounds really nice in the mid and high end (had a small headroom amp before) though i feel that it is lacking a bit in the low end in comparison, could be a bit beefier. Not sure if the small tube needs to be played in or something (the one i replaced with a new "premium" tube).
There is also zero noise so i am very pleased with that as well.

Thanks for all the help here and for a nice DIY product, was really fun to build