Tubes are not glowing

[Doc B]

Pull the 12AU7. Measure the resistance of the tube pins 4 to 9 and 5 to 9. If they both read low resistance, measure the voltage at the actual tube pins - not the solder joint - from 4 to 9 and 5 to 9 with the 12AU7 inserted.

 

[Paul Joppa]

I measured the resistance between LED legs. The one at A3 shows something and the one at A8 doesn't (of course, I tried both directions). Doesn't it mean it is dead?...

Ah, I found it (post #7 of 23) - that's what I get for jumping into the middle! I probably thought you had measured voltage, not resistance. Yes, it's probably dead. It would be nice to know how it died, in hopes that the replacement does not die immediately. Is it perhaps in backwards? Anyhow, the team is making progress.  Pay attention to PB; he designed the amp and has fixed hundreds of them!

 

[Paul Birkeland]

I measured the resistance between LED legs. The one at A3 shows something and the one at A8 doesn't (of course, I tried both directions). Doesn't it mean it is dead?

Potentially.  You can jumper A3 to A8, then check the voltages at terminals 1 and 5 again.

-PB

 

[zlib]

Pull the 12AU7. Measure the resistance of the tube pins 4 to 9 and 5 to 9. If they both read low resistance, measure the voltage at the actual tube pins - not the solder joint - from 4 to 9 and 5 to 9 with the 12AU7 inserted.

I have low resistance from 4 to 9 (actually, it changes... is it OK?) and I have nothing from 5 to 9. Does it mean the half of tube is dead?

 

[Doc B]

In a 12AU7 dual triode the heater has one end connected at pin 4. The middle is connected at pin 9. The other end is connected at pin 5. The section from 4 to 9 heats one triode's cathode and the section from 5 to 9 heats the other triode's cathode. Each half of the heater is connected to power in parallel, so if one is out the other will still heat. Thus if you have an open reading from 5 to 9 it would imply that that half of the heater is open. Be sure that it's not just oxidized tube pins, that can create a false open reading.

 

[zlib]

When I turn Crack on I see only half of this tube glowing, so if it is oxidized tube pins then they influence the work of the tube too. So, should I change this tube or not?

 

[Doc B]

If it's oxidized tubes pins you could try cleaning them. If the heater is open the tube will need to be replaced.

 

[zlib]

I tried cleaning the pins but still I have no resistance from 5 to 9. So, I will wait for new 12AU7 and LEDs, then we will continue.

 

[Paul Birkeland]

I tried cleaning the pins but still I have no resistance from 5 to 9. So, I will wait for new 12AU7 and LEDs, then we will continue.

Change the tube first.  If half the tube doesn't conduct, one LED will not light.

 

[zlib]

I have received new LEDs and 12AU7 tube and now my Crack works and sounds very well. Thanks everyone! But I also have an assembled speedball kit and I want to integrate it in Crack. Will you help me again?

Two years ago speedball upgrade made my Crack smoking. Maybe it was because of bad main Crack kit assembly (I removed speedball and reverted back to just Crack, but my Crack stopped sounding in a year), but maybe there was a mistake in speedball assembly too... Now I recheck every step from manual and one thing took my attention. There are two 2N2222A transistors on large board and manual advises to leave some space between the metal body of the transistor and the PC board. One of those transistors is soldered without leaving the space between transistor body and the board. Is it critical or not?

 

[Paul Birkeland]

A Crack that smokes after Speedball installation is due to improper mounting of the TIP50 transistors.

 

[zlib]

Actually the power supply started smoking back then. Is it TIP50 transistors anyway?

What about 2N2222A's body touching the PC board? Is it OK?

 

[Paul Birkeland]

Actually the power supply started smoking back then. Is it TIP50 transistors anyway?

A smoking power supply in a Crack after Speedball installation indicates an improperly mounted TIP50 transistor.

 

[zlib]

I checked speedball boards (double checked TIP50 transistors!), resoldered suspicious joints and then I installed speedball into my Crack. And here are my voltages:

1 - 80
2 - 150
3 - 0
4 - 150
5 - 80
6 - 0
7 - 100
8 - 0
9 - 100
10 - 80 (!)
11 - 0
12 - 0
13 - 50 (!)
14 - 0
15 - 100 (!)
19 - 60 (!)
20 - 0 (!)

A1 - 3
A2 - 0
A3 - 0.5
A4 - 0
A5 - 0
A6 - 40
A7 - 0
A8 - 1.5
A9 - ? (can't reach it now)

B1 - 35
B2 - 40
B3 - 30
B4 - 25
B5 - 45
B6 - 0 (!)
B7 - 0
B8 - 0

So, the voltages at terminals A1-9 and B1-8 are in total mess. And terminals 10, 13, 15, 19, 20 look bad too. Where should I search for a problem?

 

[Paul Birkeland]

You really didn't need to measure the voltages at A1-A9.  The voltages at terminals 1 and 5 tell enough of the story to not need that.

For instance, seeing 80V at 1 and 80V at 5 tells me that your voltage measurements at A1 and A6 aren't possible, and that you have 1.5V at A3 and A8.  This is why we don't have these voltage checks in the Speedball manual.

The voltage at 10 is very distressing, and the amplifier shouldn't be plugged in unless that is remedied.  Can you double check that terminal?  Is there any debris or component leads from 9 to 10 that might create a short circuit?

Are both the 2.49K resistors on the headphone jack still properly installed?  Do they both look to be about the same color?

 

[zlib]

The voltage at 10 is very distressing, and the amplifier shouldn't be plugged in unless that is remedied.  Can you double check that terminal?  Is there any debris or component leads from 9 to 10 that might create a short circuit?
Are both the 2.49K resistors on the headphone jack still properly installed?  Do they both look to be about the same color?

I found a problem: the wire from headphone jack to terminal 10 fell out from terminal 10 after bending caps near octal socket. So, I resoldered it and now terminal 10 shows 0. But all other terminals have the same voltages as before. Still have 0 at terminals 20 and B6, for example.

You really didn't need to measure the voltages at A1-A9.  The voltages at terminals 1 and 5 tell enough of the story to not need that.
For instance, seeing 80V at 1 and 80V at 5 tells me that your voltage measurements at A1 and A6 aren't possible, and that you have 1.5V at A3 and A8.  This is why we don't have these voltage checks in the Speedball manual.

What if some wires were broken during the installation of speedball boards? Actually, my manual from 2013 have these voltages and they are very different from mine.

Some observations during the voltage check:
1. LED from center A to A8 glows but the LED from center to A3 does not. I checked the contact from A3 to center A - it is OK, my meter shows some resistance.
2. All other LEDs on speedball boards doesn't glow. But during the previous voltage check I saw them glowing. Do I have glitches in my eyes?
3. Both tubes glows normally.

 

[Paul Birkeland]

1. LED from center A to A8 glows but the LED from center to A3 does not. I checked the contact from A3 to center A - it is OK, my meter shows some resistance.

This will result in a voltage discrepancy at either T1 or T5.

 

[zlib]

T1 means terminal 1? The voltages at terminals 1 and 5 seem fine to me. Where should I search for a problem now?

 

[Paul Birkeland]

B6 and terminal 9 are connected with a solid piece of wire.  If you have 100V at terminal 9, you have 100V at terminal B6.

I would recheck your voltages, but just terminals 1 through 10.

-PB

 

[zlib]

I noticed two bended capacitors' bodies touching the terminals. Now I moved them a little and here are my new voltages:

1 - 45
2 - 50
3 - 0
4 - 50
5 - 0!
6 - 0
7 - 40
8 - 0
9 - 0!
10 - 0

So, what should I check now?

Oh, and now one of those capacitors' bodies touches one lug of heat sinks (where TIP50 transistors are installed). Is it bad?