'VERY' loud buzz [resolved]

[El Tel]

Hi Everyone

I've a new problem with my Crack/Speedball

I inadvertently moved the 12 AU7 valve the other day whilst wearing my headphones and a VERY loud buzz/vibration came out of the right hand channel only for a brief moment, scared the life out of me. Anyway I turned the volume down to minimum and tentatively moved the valve again and the same keeps happening. Its not there all the time (which is just as well as I think it would damage the headphones), it's only for the briefest of moments every time i move the valve in it's socket, but I'm worried if this suddenly found it's spot where it introduces this noise and stayed on.
I've tried another valve and the same occurs.
Any Ideas ?

[Doc B.]

Look for a loose connection on the tube socket.

[El Tel]

Thank you for your reply Doc.
I've had time to have a look at the tube socket wiring this morning, and I noticed that one of the LEDs wasn't on, I moved the tube in it's socket which caused the LED to come back on but also reintroduced the loud buzz/vibration on the right channel.
Now that LED won't come on at all now, but the Amp is still playing out of both channels in the headphones (albeit the right channel is down on volume) .
Look forward to your thoughts again.
Many Thanks
Terry

[Doc B.]

You may recall that I was talking about loose connections in my post. Did you look closely for loose connections? Typically a loud buzz means that a connection to ground has come loose. The LED being on, then off, the buzz coming and going, etc. could indicate that some connection is intermittent. Carefully nudging the connections with something insulated like a pencil or a wooden chopstick while the amp is on can help you to locate the exact point where the connection is flaky.

[El Tel]

Hi Doc

I didn't really get to test for loose connections on the tube socket, as I was distracted by the fact that one of the LEDs was out, and by wiggling the tube it came back on.
I guess that the centre pin connection is OK, as surely both LEDs would be out ? I need to check the other end of the LED that was intermittent, great idea with the chopstick!
I've ordered some LEDs incase that one is shot and I'll take another look next weekend, have a good evening, and I'll let you know the outcome 👍

[Paul Birkeland]

I didn't really get to test for loose connections on the tube socket, as I was distracted by the fact that one of the LEDs was out, and by wiggling the tube it came back on.
I guess that the centre pin connection is OK, as surely both LEDs would be out ?

If the LED that is turning on and off is not well connected at the center pin, then this could cause your issue. 

It is worth noting that any of the connections on the 9 pin socket related to that half of the 12AU7 could cause the LED to turn on and off, and even some of the parts on the adjacent 5 lug terminal strip.  It would be a mistake to remove and replace the LED that is turning on and off over and over again without doing the chopstick test to determine what's actually not well connected.

[El Tel]

Great Advice Paul, I'll certainly go through it all this coming weekend, now where are those chopsticks 😀

[El Tel]

Morning guys

I've just replaced the failed LED on the ECC 82 socket and it's still not lighting up.
I have now noticed that two of the LEDs on the small pcb of the Speedball are not lighting up also (on the OA side), should I go ahead and replace these too ?

[Tom-s]

Don't look for the issue with the leds themselves. The fact they're not lighting up is a symptom, not the problem.
Make sure both halves of your ECC82 are lighting up (could be one half is out?).
If all OK solder the center pin of the transistor again on the side that the leds aren't lighting up.
If all checks out, start with voltage checks and post here.

[Paul Birkeland]

Morning guys

I've just replaced the failed LED on the ECC 82 socket and it's still not lighting up.
I have now noticed that two of the LEDs on the small pcb of the Speedball are not lighting up also (on the OA side), should I go ahead and replace these too ?

I never saw any reason to believe the LED needed to be replaced.

I have now noticed that two of the LEDs on the small pcb of the Speedball are not lighting up also (on the OA side), should I go ahead and replace these too ?

No!

Please post the OA and OB voltages on the front C4S board.

[El Tel]

Ok, this is where I'm at, so far.
OA is 180  OB is 66

Also, the voltages on the terminals read as follows,
Terminal 1 = 180
Terminal 2 = 182
Terminal 3 = 0
Terminal 4 = 182
Terminal 5 = 66

Terminal 6 = 0
Terminal 7 = 178
Terminal 8 = 0
Terminal 9 = 103
Terminal 10 = 0

As to regards the LEDs, I have

The four on the Speedball large board - all 4 on.

The four on the small Speedball board - D1 (A side) is on and bright. D2 (A side) not on.
D1 (B side) on but dim
D2 (B side) on but dim

Thanks

[Paul Birkeland]

Carefully measure the DC voltage at A8?

If you see ~12V here, then you do indeed have an issue with the LED there. 

If you see 0V here, then you'd want to look at the tube itself while the amp is on to be sure both halves of the tube are glowing.  If they aren't, then you probably have a bad solder joint at A4/A5 that isn't allowing both halves of the tube to heat up.

If this Speedball was freshly installed, we would also remind you that the center legs of the MJE350 transistors are difficult to solder properly and require some extra heating. 

[El Tel]

Hi Paul

Thanks for your reply.
Really not sure what is going on as I did a few voltage tests around the 6080 tube socket, and when I tested B1 I got a spark and now don't have any reading (zero volts) at OA on the Speedball board and at B1.

I tested A8 and there is 0.8 of a volt.

I'm tempted to buy a new set of valves to see if that sorts things out.

PS This is not a new Speedball installation, it's been up and running since about 2 years or so ago with no problems until I accidentally moved the au7 valve and noticed a loud buzz every time the valve was jiggled.

[Paul Birkeland]

I'm tempted to buy a new set of valves to see if that sorts things out.

What is leading you to believe the tubes are bad?

You will need to do a voltage check on terminals 1-10 for us to proceed any further.  It's possible that the fuse has blown in your amp when the arc was drawn. 

[El Tel]

Morning Paul

I've checked the voltages and here's what they are

1 = 0 volts
2 = 200
3 = 0
4 = 200
5= 69

6= 0 Volts
7 = 70
8 = 0
9 = 111
10 = 0

Checked the fuse and that's all good