Bad tube? Upper TIP50 does not work in Speedball

[Gauss]

I've just completed my Crack with Speedball.
The biggest tube does not glow and it's always cold. The upper TIP50 (the closest to the biggest tube) on the Speedball stays cold and leds does not get on, the lower TIP50 it's really hot, leds get on.

I get the next voltage readings:

B1 = 73V
B2 = 209V
B3 = 1.4V
B5 = 209V
B6 = 209V
B7 = 0V
B8 = 0V

Pins 6, 7, 9 and 10 on the transformer are 98V
13 = 210V
14 = 0V
15 = 223V

Pins on the lower part, close to the small tube:
4 = 208V
5 = 77V
9 = 210V

Pins close to the transformer:
18  98V
19  97V
20  0V
21  235V

I don't have tubes tester nor other tubes. Should I get a new tube? Actually my big tube it's RCA and looks with sticky and old dust on the glass.

Thanks

 

[Doc B]

The 6080 does not glow very brightly but it should get hot. From your description it sounds like one problem may be that the 6080 heater isn't getting voltage. Measure AC volts between pin B7 and B8. You should see around 6.3 volts AC.

 

[Gauss]

It reads 6.77V AC between B7 and B8

 

[Doc B]

OK if voltage is getting to the heaters then the next step would be to check all of the solder joints on the connections on the PC board and the half of the tube where the LEDs are not lighting up.

 

[Grainger49]

Do still check the other tube.  Also rewet the solder joints on the heaters from the transformer through to the last tube.  You might get a voltage reading but it might not be a good connection.  With the high voltage coming in and the heaters properly heated the only thing left will be the cathode circuits.

If the tube has too much voltage on the plate, and the heaters right, then the cathode circuit is probably incomplete somewhere. 

 

[Gauss]

By cathode circuit you mean the circuit around the transformer where the caps are? Last night I checked all my solder joints and even retouched the tube terminals and on the caps. Still nothing.

I also found that th TIP50 that stays cold receives current and the resistors on it's side are hot as the other side of the board with the other TIP50. I'm thinking that maybe the TIP50 is not working, don't know however if that's the reason why the tube doesn't work, maybe both things. If I can tomorrow I'll get 2 more TIP50 and 2n222, also I'll try to found some tubes on "the electronic street" on my city. Maybe this would have to be on Saturday.

This night I'm going to give it another try but on the lower tube and everywhere else.

 

[Paul Joppa]

A very common problem is soldering to the middle lead of the power transistor (TIP50 here). That lead is connected to the heat sink, making it difficult to get the lead hot enough to flow the solder. If the cold TIP50 is connected to B6, that would explain the high voltage there.

The other triode section is B1-B2-B3, and the B1 and B2 voltages look right. The very low voltage on B3 indicates a near short circuit to ground. My first guess would be a solder bridge on the PC board at the current-set resistor, but there could be many other explanations. You might check again that the right leads are in the right holes, especially the small transistor, when you are looking for solder bridges.

 

[Grainger49]

By cathode circuit you mean the circuit around the transformer where the caps are? Last night I checked all my solder joints and even retouched the tube terminals and on the caps. Still nothing.  .  .  .   

The cathode circuits are pins 3 and 8 on the 12AU7 and pins 3 and 6 on the 6080.  I don't see those going to the transformer at all.

At this point it would be good to go back through all the voltages and post anything that is greater than 15% out of specification.

 

[Gauss]

Alright I took another go, desolder the speedball, checked both TIP50s, transistors are fine, resolder joints everywhere, rechecked everything, solder again the speedball and nothing.

But now I'm aware of something, between B5 and B6 I read a short circuit when the 6080 is on the circuit. So I removed the 6080, read again B5 and B6 and no short circuit, read pins 7 and 8 on the 6080 alone and it reads as short with 1 ohm..... here's when I realized that the socket was in the wrong position! duh!!!

Desolder everything on the 8 pin socket, repositioned it and the good news, my Crack it's finished! It's working amazingly good!! I took the time to take one photo and puting it on the gallery, my Crack it's burning the same as my emotions, I listened a while to Norah Jones and was such an outrageous experience, I had to removed some tears from my face

Thank you Doc, thank you Grainger49, thank you Joppa and thank you Bottlehead!! Now tomorrow it's the time to pair my HD600 to my Crack!! =D