Tubes are not glowing

[Paul Birkeland]

Can you carefully measure the voltage at A7?  80V at A8 has several causes, but is something we can deal with fairly easily.

One glowing LED on the socket means that at least half of the tube is glowing.  This can happen if the wire connecting to A4 and A5 is only making a good connection to one of those pins.

[zlib]

It's very hard to see but yes, I see now how the half of little tube glows. So, the second LED is definetely dead. But my voltages show different values now. Or maybe it is because of different meter?.. Anyway, here are all voltages (the values are rough because I use analog meter):

1 - 150 (!)
2 - 160
3 - 0
4 - 160
5 - 80 (!)
6 - 0
7 - 150 (!)
8 - 0
9 - 100 (!)
10 - 0
11 - 0
12 - 0
13 - 160
14 - 0
15 - 190
20 - 0
21 - 210

A1 - 80
A2 - 0
A3 - 1.5
A4 - 0
A5 - 0
A6 - 150 (!)
A7 - 0
A8 - 0 (!)
A9 - 0

B1 - 150 (!)
B2 - 170
B3 - 150 (!)
B4 - 80
B5 - 170
B6 - 100
B7 - 0
B8 - 0

I marked the suspicious values with "(!)" mark. I don't know which value must be different because of 230 V country (manual provides values for 120 V country). But looks like I must have equal values at terminals 1 and 5, 7 and 9, A1 and A6. Maybe they are different because of one dead LED? Also, I have 0 V at terminal A8 (because of dead LED, I guess) and suspiciously high values at B1 and B3.

So, I ordered new LEDs. Will it solve all suspicious voltages or not?

[Paul Joppa]

The voltages are consistent with half the 12AU7 not glowing, as PB said. If the tube cathode is not heated (glowing) then no current can go through the LED. There is no evidence yet that there is anything wrong with the LED itself. Again, as PB said, look at A4 and A5; one of them is probably a bad solder joint.

[zlib]

There is no evidence yet that there is anything wrong with the LED itself. Again, as PB said, look at A4 and A5; one of them is probably a bad solder joint.

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?
A4 and A5 looks fine for me. I have 0 Ohms between power transformer terminal 4 and A4/A5. It means they have good joints, I guess.

[Paul Birkeland]

Can you see both halves of the 12AU7 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?