A tube Killed my Amp Part 2 [resolved]

[TRTim]

Ok so I made a trip (online) to Mouser and got the parts to rebuild the main speedball board. Spend this evening putting the board back togeather. I actually enjoyed getting back into building electronics, maybe I will modify it.Anyway, first things first. Below are my readings:

1- 67
2- 164
3- 0
4- 164
5- 142
6- 0
7- 98.2
8- 0
9- 145.2
10- 0
11- 0
12- 0
13- 164.5
14- 0
15- 187.2
20- 0
21- 209.4

I think this means the speedball board is out and needs rebuilding (the two transistors). Please let me know. Thanks

Also what do you think about putting in a standby switch to warm the heaters and tube before hitting them with the full voltage. Something simple like a 5W 20 ohm resistor and a toggle switch. The GEC 6080 is a rare tube and I want them to last.

Tim

 

[Paul Birkeland]

5- 142

That's where you need to focus.  Are both LED's on the socket lit up?  (If one isn't lit up, don't take the time to dig it out any replace it, it's just an indicator of potentially a different problem)

Your voltages do not necessarily indicate a problem with the larger board.  If there is a problem with the larger board, getting the voltage at T5 in spec will be required to know one way or the other.

-PB

 

[TRTim]

Yes both LEDs are lit up on the socket.

I was thinking that one of the smaller boards is out and this is why I am getting such a high voltage on T5.

 

[Paul Birkeland]

Pull the 6080 and leave in the 12AU7, then measure the voltage at T5 again.

If the voltage at T5 stays high, what is the voltage at A2?

Since this is a new thread, I don't have the details in front of me about the original problem, but can you confirm that the voltage at T5 once measured properly?  With the first generation of Speedball kits, the R1 resistors all appeared to be physically the same, except for the colored stripes on the resistor bodies, and accidentally swapping a 31.6 Ohm resistor with a 237 Ohm resistor will cause issues similar to what you are having. 

 

[TRTim]

First of all thanks for you time.

So the background is that the Crack with speedball has been up and running for the past two years. Recently when I turned it on the GEC 6080 went off in a spectacular display of sparks and noise. After changing it out to a new one I only had sound in one side of the amp. I noticed that the leds on the main Speedball board weren't lighting.  I replaced the leds and no difference. I posted my issue and is was suggested that the tube may have taken out one or both of the transistors. Replaced all the trasitors on the main board and that is where this post begins.

So I thought is may be the smaller board of the Speedball may have got fried too. I just finished replacing all the trasistors and viola I am up and running again. All the values are back in tolerances and it sounds great. I really missed this amp.

Anyway mark me as solved.