Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Jimb0 on January 25, 2020, 09:48:36 AM
-
Just finished building a Crack with Speedball. Voltages checked out okay but I am not getting any sound. I tried using both my laptop and desktop.
-
N/m it's my Modi Multibit that stopped working.
-
Actually yes there is something wrong with the sound. It's very low and I can't get the volume to go up.
-
ok so i'm getting 1.7v at OB and OA
-
At which OA/OB, the big board or the small board? Are both tubes glowing?
-
Yes both tubes are glowing and OA and OB on the big board
LED's light up on the small board and the two at the bottom but not on the big board
-
What DC resistance do you get between OA and OB and ground on the big board? As always build photos can help too.
-
OB and OA reading infinity. Ground is reading 40 ohms.
Pics
https://imgur.com/a/eYBPLEj
-
If you pop each wire out of the big board, you can take it all the way out of the amp, then just temporarily solder the 3K resistors onto the end of those wires. It would be helpful to know if the amp works under those conditions. Also, are the voltages on the small boards OK?
-
I no longer have any 3K resistors to test it, is there another way? I'll recheck the voltages soon
-
I would obtain a pair of 3K resistors so that you know if the amp is otherwise working without the big Speedball board. This is what I would do if I had your amp on the bench for repair.
-
Will do PB
-
Do I need the 22.1 KR ½W resistors as well?
-
OA and OB on the small board is 72v
OA and OB on the big board is 2v
B+ is at 217 on the big board
-
You can leave the small board in and just tack the 3K resistors onto the wires poking up that would hold the big board.
-
just to be sure the 3K resistors are the ones that came with the non-speedball kit?
-
Yes.
-
Just wanted to make sure I did this right
https://imgur.com/a/Kb6eKIB
also what voltages should I be checking here?
-
7 and 9.
-PB
-
219v at 9
6v at 7
-
For all of the connections on the octal socket, I would pull a little more wire through them and wrap it around the socket.
The 219V at terminal 9 makes me wonder if one of the black wires in the amp is loose.
If you happen to have a spare 6080/6AS7G sitting around, it wouldn't hurt to give that a shot as well, but having both 7 and 9 so far off in different directions would tend not to suggest a bad tube.
-
Good morning PB. I rechecked the black wires and couldn't find anything that was loose, but I resoldered them just in case. I don't have a spare 6080 at the moment so I can't test it. However, my 6080 tube is a bit loose at the base (the metal part at the bottom), if that means anything. Rechecked the voltages and got the same readings at 7 and 9.
On another note, I actually remember hearing a noise the first time I turned the amp on a week ago. I'm not sure where the noise was coming from but it stopped working shortly after that. I had a spare 6080 tube (but later sold an amp with the tube) and tested that but by that time the big board stopped working. Do you think maybe the 6080 tube was the one making noise and is it possible that it messed up the big board?
I will buy a spare 6080 for testing.
-
Is one 3K resistor getting much hotter than the other? You can run the amp for about 60 seconds, then shut it down and wait about 20 seconds, then safely touch the resistors.
The disparity in the voltages would make me wonder if both resistors would be cold.
-
yes both 3k resistors are cold
-
So 219V DC across a 3K resistor will dissipate 16W. That won't be enough to completely blow the resistor immediately, but it will get very hot in a hurry. Since it isn't getting hot, this is almost certainly an issue of loose connections in the amp not properly conducting and giving anomalous readings.
-
PB, I just resoldered every joint in the amp and paid close attention to the connections in the octal socket but I'm still getting the same readings.
-
What DC resistance do you get between terminal 12 and terminals 7 and 9?
-
Hello JimbO and Paul. Paul correct me if I am wrong. In the above photo it appears that the 10K cathode resistor on the left side is connected to B+ which is flowing through it to the output cap which is shorting to ground through the head phone jack?? That resistor should be connected to the same ground point that the resistor on the right is connected to?? Don't plug your phones in!
Chris/AB2KH
-
Good eyes Chris, I didn't even notice that!
-
Sorry, I meant 3K @ 10 watt resistor. Just to clarify,don't want confuse the confusion.
-
Thanks Chris. So both are suppose to be connected to 3U like in the original build without Speedball?
-
JimbO , Yes. Disconnect the left side resistor from the red wire, move the red wire out of the way, or better yet remove it from the terminal lug altogether, It has B+ on it. Connect the resistor lead that you just disconnected and solder it to the same point that the resistor on the right is connected to the black wire (ground). That should be the non speedball configuration. (Disclaimer) Please do not do any fufther testing of your amp until Paul (whom is the official expert on this Bottlehead Forum) confirms that this is correct, I do not want to be responsible for injury to you or damage to your amp.
Chris
-
Thank you Chris! Will do!
-
PB I went ahead and tested it and getting 18v at 9 and 9v at 7 now
-
I would test it with a different 6080, though it would be super unlikely to get one with two bad halves. Can you confirm that it doesn't say 6082 on the glass?
-
Sure. My new 6080 comes in tomorrow. Most of the markings have faded away so I can't read it. The brand is National. Here are some pics of it.
https://imgur.com/a/DLFl115
-
6080 tube arrived today. Rechecked voltages. Both 7 and 9 are now reading 105v.
-
Sounds like maybe a 6082 sneaked through somehow.
-
Thanks PB as usual. Everything is working properly now. Cheers!