Speedball Voltage [solved]

[dave601]

i've just done with the speedball upgrade. The Crack that I assembled before worked perfectly The 12AU7 doesn't glow. However there are something that dont seen to be right with the speedball.

- On the small pcb, the led on the left doesn't light up at all, the other next to it is barely glows. Same thing happens to both pcbs (A and B).

- The voltage
Terminal          Voltage (VDC)
1            181
2            183
3            0
4            183
5            181
6            0
7            181
8            0
9            181
10          0
11          0
12          0
13          183
14          0
15          200
29
18          79
19          76
20          0
21            117
A1          181
A2          2
A3          2
A4          0
A5          0

B1          181
B2          183
B3          180

I            183
O          181
I'm quite sure that the leds and transistors (2n2222a and 2n2907a) were assembled correctly. This maybe a dumb question but I did use some wire from the crack kit for the speedball, is that ok?

 

[Paul Birkeland]

If the 12AU7 doesn't glow, the Speedball voltages will never be correct.

The 12AU7 is made to glow by the twisted pair of wires that feed A4/A5 and A9, that's where I'd start.

-PB

 

[dave601]

it doesn't glow but i does get very hot. I reheated every joints.
assuming that there's no cold joint at A4, A5, A9, B8, B7. Where should I check next?

 

[Paul Birkeland]

Can you look at your Crack in a dark room to be sure the 12AU7 isn't lighting?

Do the LED's on the 9 pin sockets illuminate?

 

[dave601]

the leds in 9 pin sockets glow brightly.
the 12AU7 doesn't light up at all, I checked it last night in a dark room.

 

[Paul Birkeland]

The LED's on the 9 pin socket won't glow unless the 12AU7 is functioning (and lit) so I think we can ignore this issue.

When you X'd out that your Crack worked perfectly before, can you elaborate a little more on this?  Was the amplifier functional?

I'd focus on the two small green PC boards first.  Are the correct wires going to the "I" and "O" pads? (terminals 2 and 4 go to "I", 1 and 5 to "O")

I'd also recommend reheating the center leg of each MJE350, as those can take a bit of heat to solder properly.

-PB

 

[dave601]

here's some pictures http://imgur.com/a/oVSCz
before installing speedball, the amp was running with no problem expect the small tube didn't light up. It sounded good as well.
I tried reheated the MJE350 on each board but it doesnt work 

 

[Paul Birkeland]

All your symptoms could be explained if you swapped the 237 and 31.6 Ohm resistors.

-PB

 

[dave601]

First time I checked the voltage of the speedball I accidentally touched both terminal 1 and 2 with the lead and it ignited. As far as i can remember the leds were illuminating a little bit before it. 

 

[dave601]

All your symptoms could be explained if you swapped the 237 and 31.6 Ohm resistors.

-PB

Thank you so much Paul, I'm going to swap them right now.

 

[Paul Birkeland]

Well, you can measure them in the circuit, don't just swap them arbitrarily because it's a possibility.

 

[adamct]

Just to be clear: Paul didn't mean "Swap the 237 and 31.6 Ohm resistors". Instead, he meant "Check to see if you accidentally mixed up the 237 and 31.6 Ohm resistors during your initial build, since that would explain the symptoms you are having."

Obviously, if you did mix up the resistors, then you would have to fix the problem by swapping them into their proper positions. I just wanted to clarify so that in case you did NOT mix up the resistors, you wouldn't be swapping them now unnecessarily, and then have to swap them back yet again!

Best regards,
Adam

 

[adamct]

Whoops. Paul posted while I was typing. He said it more succinctly!

 

[dave601]

thanks guys.
the measurement is perfect now and it sounds beautifully too.
but I still don't know why my 12AU7 isn't glowing at all

 

[Paul Birkeland]

Ah, excellent!

The heaters in your 12AU7 may just be completely covered, or the getter at the top of the tube may just be unusually large. 

Either way, I'm glad that you're up and running!

-PB

 

[Grainger49]

Try an RCA "cleartop" 12AU7.  You should see the glow.

Not seeing the glow is a function of that tube, not 12AU7s in general.