Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: The Expanding Man on March 31, 2011, 02:32:53 PM

Title: Help Problem Solve my build
Post by: The Expanding Man on March 31, 2011, 02:32:53 PM

I'm having difficulties with my Crack build.

I have checked the wiring 3 times and it seems to be OK.

All of the resistance checks at page 37 of the manual are spot on.

It is a 240v version of the kit.

My voltage checks are unusual.  I will post where they differ with the values specified at page 38 of the manual.

Terminal  Voltage
1             -0.77
2             -0.77
4             - 0.79
5             -0.79
7              6mv
9              3.5 mv
13            -0.78
15            - 225
21            - 225

A1            -0.78
A3            0.6
A6            -0.78
A8            0.68

B1            -0.78
B2            -0.78
B3            5.8mv
B4            -0.78
B5            -0.78
B6            3.4mv

Both tubes glow, although the 12AU7 seems a bit feint to my eyes.

I've built a few pcb amps over the years, but this is my first experience with point to point.

Thanks.

Title: Re: Help Problem Solve my build
Post by: Doc B. on March 31, 2011, 02:39:24 PM

Sounds like the heater supply is OK, but the B+ readings are funny. Check the orientation of the stripes on the UF4007 rectifier diodes and the electrolytic capacitors. 

Title: Re: Help Problem Solve my build
Post by: The Expanding Man on March 31, 2011, 02:46:27 PM

Quote from: Doc B. on March 31, 2011, 02:39:24 PM

Sounds like the heater supply is OK, but the B+ readings are funny. Check the orientation of the stripes on the UF4007 rectifier diodes and the electrolytic capacitors. 

Thanks Doc B,  I will check them again when I get home from work.  They did appear to be OK when I previously checked them.

Title: Re: Help Problem Solve my build
Post by: The Expanding Man on March 31, 2011, 11:11:16 PM

OK, I found my first fault that seems to have caused the problem with the voltages above - I'd missed a solder joint.

However, some of my voltage tests are now too high, and the led at A8 doesn't illuminate. I  obviously have another fault.

Abnormal voltage tests:

Terminal  Volts

1             142
2             158
7             141
A6            142
A8           12.8  (and the led doesn't light)
B1           142
B3           141

I was curious to see if these results were within the normal variations so I tested the amp with cans.  I got a signal in the left channel but nothing in the right channel.

Any ideas as to where to start troubleshooting?

Title: Re: Help Problem Solve my build
Post by: Paul Joppa on April 01, 2011, 10:09:18 AM

The LED at A8 must be not soldered well, in backwards, or damaged. You have voltage at A6, and at A8, so that triode is getting power and it is conducting. The LED should limit the voltage at A8 to 1.6 volts or thereabout.

Title: Re: Help Problem Solve my build
Post by: The Expanding Man on April 01, 2011, 01:42:40 PM

Thanks Paul, thanks Doc B, you were both right on the money.

It's Alive!
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.korpg.com%2Fblog%2Fwp-content%2Fuploads%2F2010%2F04%2Fits_alive1.jpg&hash=509f5af2808bc9461953f6aaae7a4af3eb46bdb6)


Any ideas as to optimal burn in time?

I wouldn't mind getting familiar with the amp before I add the speedball.