LED problem in Finnish Crack

[TT]

Hello,

I just finished my Finnish Crack.

The resistance check was OK except terminals 6 and 10. They were 0 ohms (expected 2.9K ohms) but I thing that also those zero-readings are OK because I have connected the 1/4" jack unused solder terminals to the ground.

But when I made voltage check I noticed that the terminal 3 LED wasn't glowing and all voltage readings was significantly too high. I got:

1: 129 V (expected 90 V)
2: 266 V (170 V)
4: 267 V (170 V)
5: 129 V (90 V)
7: 176 V (100 V)
9: 168 V (100 V)
13: 278 V (100 V)
15: 313 V (185 V)
21: 347 V (206 V)
A1: 133 V (90 V)
A3: 2.5 V (1.5 V)
A6: 133 V (90 V)
A8: 19 V (1.5 V)
B1: 225 V (90 V)
B2: 267 V (170 V)
B3: 224 V (100 V)
B4: 132 V (90 V)
B5: 268 V (170 V)
B6: 168 V (100 V)
All the terminals expected 0 VDC were fine.
Mains voltage is 230 VAC and my Crack is the 240 VAC version.

My problem is that in local shop they don't have HLMP-6000 Red LEDs when I tried to buy a new one. Can I use some other LED type instead HLMP-6000? 

Timo

 

[Paul Birkeland]

Your LED's aren't the problem.

I am guessing that the tubes glow visibly?

Is the black wire present that connects to the center lug on the 9 pin socket?

Are you 100% sure that the single black wire leaving the power transformer area and heading up to the headphone jack is connected to 12 and not 11?

 

[TT]

Thank you for the quick reply!

Yes, both tubes are glowing and the wires you mentioned are correct.

 

[Paul Birkeland]

It looks like possibly the other black wire feeding 12 is broken off?

 

[TT]

No, the other black wire feeding 12 is not broken off - I apologize the poor picture quality. I don't know is that a adequate measurement, but I got 0 Ohms between 12L and 14L and 0 Ohms between 14L and the headphone jack.

 

[Paul Birkeland]

Philosophically - your Crack is wheezing.  It's attempting to draw current, but not successfully.  From what I can gather, I would recommend re-flowing all of the solder joints that contain ground wires (the black wires on the two 6-lug strips, the lowest lugs on the headphone jack, terminal 3, and the black wires on the volume control). 

Can you measure the AC voltage between terminals 4 and 5?

 

[TT]

Light at the end of the tunnel: the meter that I used earlier is probably out of order!

To day I used other meter and now the readings are much better. But still some DC-voltage readings are not in tolerance. And the A8 LED don

 

[Paul Birkeland]

OK, this is looking more reasonable.

The high voltage across that LED indicates a poor solder joint on one or both ends (usually), or potentially an issue with the wire feeding A7.

While you are at it, I would also resolder the joints on the 22K resistor that feeds A6, just to be comprehensive.

You're getting pretty close on this one, as half the amp is working properly.

 

[TT]

Thank you Paul!

I will resolder those joints.

Timo

 

[TT]

Hello again,

I resoldered joints on the wire feeding A7 and also the joints on the 22K resistor that feeds A6, but bad voltage numbers are unchanged!

I

 

[Grainger49]

I don't see a check of the HLMP 6000 orientation at pin A8.  Is the silver band the same as it is for the A3 LED?

 

[TT]

Yes, the A8 LED orientation is same as it is for the A3 LED. The  silver band side is connected to the center pin.

 

[Grainger49]

That is correct.  The HLMP 6000 is the only thing in the cathode circuit.  Very often when the tube is not turning on it is because of the cathode circuit.

If the A3 LED is glowing then the ground wire is secure.  Chasing back up that circuit there is a resistor on the terminal strip that ends up at A6.  Measure resistance from A6 to both ends of that resistor.  One end should be under an Ohm, the other end should be the full resistance of the resistor.  This just checks to see if the circuit is complete for the second half of the tube.

 

[TT]

Those resistance readings are 1.0 Ohms (meter scale was 0...200 Ohms) and 22 kOhms.

 

[Grainger49]

That checks out the cathode side and the plate side.  The high voltage connection back to the larger tube must be good, the other side of the small tube works. 

Did you check the heater voltage on the A tube.  It should be good if the first half of the tube is conducting.

So it has to be something with a bad connection.  Remove and insert the small tube 6 or 8 times.  It could be that the tube pins or socket might not be clean.  Even though these were new parts when you built the kit, they could have been on the shelf for years.

And, sadly, I will also recommend you wet the solder joints at A6, A7, A8, Terminals 1, 2 and the center pin of the A tube socket.  Pull the tube out first, I assume you have been doing this.  Otherwise it might get soldered into the socket permanently. 

Hey Paul!  Shouldn't terminals 1 and 2 be the same voltage if the tube is not conducting?

 

[TT]

Grainger, thank you for yours suggestions. I will try them tomorrow.
I am novice with tubes. Is the A -tubes heater voltage between A7 and A9?

- Timo -

 

[Grainger49]

Should be either A4 or A5 and A9.  A4 and A5 are tied together with that bare wire.

 

[TT]

I measured the heater voltage between A4(A5) and A9. It was zero!
Also voltage B7- B8 was zero and on transformer voltage between terminal 4 and terminal 5 was zero.

 

[Grainger49]

Ok, I should have said this, it is AC voltage because it comes straight off of the transformer.  It would read zero on the DC scale.  Sorry!  That is important information I left out.

Terminal 4 to terminal 5 should be the DC drop across the plate resistor, 22.1k Ohms.  If the tube is not conducting, it will not drop any voltage.

 

[TT]

Oh no! I should understand that! The heater voltage is 5.5 VAC.