Low noise + wrong voltages

[vermeil]

Hello, I hope you can help me.

I've built the Bottlehead Crack + Speedball a while ago and at the time the measurements were correct. I used it again recently after a long break and have now noticed the sound in the right channel is lower than in the left. The measurements I've taken aren't quite correct either and I can't place why:

large tube: B1 73 V, B3 108 V, B4 and B6 175 V

small tube: A6 73 V, A1 175 V

small board: 0A 73 V,  0B 175 V

big board: 0B 106 V, 0A 175 V

 

[Paul Birkeland]

Half of your 12AU7 isn't conducting.  This can happen for a very, very wide variety of reasons.  Here are some things to check.

1.  Do both halves of the 12AU7 glow?  If not, the solder joints at A4 and A5 need to be reheated.
2.  Is one LED out on the 9 pin socket?  If so, DO NOT go at the LED with your soldering iron, but carefully measure the terminal where the dead LED lands (A3 or A8).  If it's about 12V, you may just have a broken LED.

These are the places where I would start, if those checks don't yield any results nor information, let us know.

-PB

 

[vermeil]

Thank you so much for your reply.

1. Both halves of the 12AU7 glow.
2. Both LEDs for the right channel don't seem to light up - but we do measure voltage (ca 175 and 182 V). The voltage for A3 and A8 is 1.5V

 

[Paul Birkeland]

Can you unplug the 6080 and see if that changes the voltages coming out of the small board?

 

[vermeil]

Here are the new voltages:

small board:
0A 71V
0B 206 V
1A 214 V
1B 214 V

 

[vermeil]

Is there anything more I could try? I do not know what else I could do and would appreciate any input.

 

[Paul Birkeland]

Could you post a picture of the bottom of your front C4S board?

 

[vermeil]

By the front C4S board, do you mean the small green one?

Would this be correct?

 

[Paul Birkeland]

One side of that board is not well soldered.

 

[vermeil]

We went over the soldered spots again and the voltages have not changed

 

[Paul Birkeland]

The 1.5V at both A3 and A8 in conjunction with the high voltage at OB on the small board would have me looking for pins touching on the bottom of that C4S board that shouldn't be, and also double checking that a 12AU7 is installed in the 9 pin socket.  The solder joints on the bottom of that PC board make it look like half of the components were replaced at a certain point, is that possibly related to what's going on?

Could you post some more photos of the build? (including the top side of the PC board)