Tubes are not glowing

[zlib]

3 years ago I was a happy owner of Crack but one day left channel stopped working, then the other. I didn't solve the problem and left Crack for better times...
Some weeks ago I decided to revive my Crack but I found a lot of rust on RCA jacks and screws (ambient conditions were not very good). I changed RCA jacks, volume pot (Alps 100K) and headphones jack. Also I changed two large ceramic resistors (3K 10W) for another pair (3K9, 10W) and changed some wires to Oyaide 18 AWG. So, I disassembled my Crack and rebuilt it from scratch.
In previous topic we solved the resistance check problem: http://bottlehead.com/smf/index.php?topic=8417.0 Now I have another problem. When I turn it on the tubes are not glowing.
I checked power entry socket and power switch - they show signal from one side to another. The capacitors show some signs of life too (the values on my meter gradually change). So, where the problem might be? Is it power supply, bad tubes or something else? Is it safe to do a voltage check if the tubes don't glow?

 

[zlib]

Is it safe to check voltages if the tubes don't glow?

 

[kgoss]

Start with the resistance test.  If you pass that then move on to the voltage test.

 

[Doc B]

Since your first issue was resolved by resoldering a questionable connection I would suggest reflowing your solder joints with a hot iron one more time to make sure they are all conducting. Run the resistance check again, and then check voltages.

 

[Paul Birkeland]

Also I changed two large ceramic resistors (3K 10W) for another pair (3K9, 10W)

That's not a suitable replacement.

A voltage check will help locate the problem.

(The aftermarket headphone jack and volume pot with pins in conjunction with stranded wire will render your Crack very difficult to repair in the future)

 

[zlib]

Here are my voltages. Please, be aware that I live in 230V country.

Terminal - voltage
1 - 220
2 - 240
3 - 0
4 - 240
5 - 220
6 - 0
7 - 0
8 - 0
9 - 0
10 - 0
11 - 0
12 - 0
13 - 230
14 - 0
15 - 240
20 - 0
21 - 240

A1 - 230
A2 - 0
A3 - 0
A4 - 0
A5 - 0
A6 - 230
A7 - 0
A8 - 0
A9 - 0

B1 - 230
B2 - 240
B3 - 0
B4 - 230
B5 - 240
B6 - 0
B7 - 0
B8 - 0

 

[zlib]

Looks like everybody are too busy to help me further (or my problem is too difficult)... Meanwhile I found bad joint at terminal 12 and resoldered it. Also one of the LEDs (from center to A8) looks dead (my meter doesn't show anything in either direction). Is this LED the source of my problem or is it just a result?

And some update on resistance check. I have 3.8K on terminals 7, 9, B3, B6 (because my big resistors are 3K9 10W, I guess). Is it fatal or not?
Also the resistance on terminal 13 doesn't change slowly like the manual says, it changes chaotically in both directions. Is it normal?

 

[Doc B]

Once you make a change like fixing the bad solder joint at 12 it is time to remeasure your voltages and post any terminal voltages that are not to spec, as they have probably changed.

 

[zlib]

I remeasured voltages but they are the same as I posted earlier.

As you can see, I have nothing on terminals 7, 9, A3, A8, B3, B6 (but there must be something as manual says). The resistance check is OK now (with the exception of 3.8 KOhms on terminals 7, 9, B3, B6 instead of 2.9 KOhms - because of different resistors). And the LED from center A-pin to A8 looks dead (is it the source of all problems or is it just a result?)

 

[Paul Birkeland]

What is the AC voltage between power transformer terminals 4 and 5?  That is the origin of the voltage that causes the tubes to glow.  Without tubes glowing, you will have the symptoms you describe.

-PB

 

[zlib]

Meter shows something about 5.8 V between power transformer terminals 4 and 5.

 

[Paul Birkeland]

Now measure AC voltage between B7 and B8.

 

[zlib]

Between B7 and B8 I have 0.

 

[Paul Birkeland]

Ok, well, one of the two wires going from power transformer terminals 4 and 5 isn't making contact over there.  This can be a soldering issue or a broken wire.

-PB

 

[zlib]

Ok, well, one of the two wires going from power transformer terminals 4 and 5 isn't making contact over there.  This can be a soldering issue or a broken wire.

Thanks! That was the case! I attached the wire from power terminals 4 and 5 to B7 and B8 but didn't solder them at B7 and B8. Now the big tube glows but the little one doesn't. Only one LED glows and the other (at A8) doesn't.
Now the voltages at mentioned terminals are:
7 - 150
9 - 100
A3 - 0 (but the LED glows here!)
A8 - 80 (the LED doesn't glow here!)
B3 - 150
B6 - 100

The difference between 7 and 9, B3 and B6 may be because of the dead LED at A8? So, I just need to replace it and everything will work OK, right? Or do you see another problem in my voltages?

 

[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?