Resistance check (solved) now voltage problem (solved)

[lordnikon]

I just finished building the Bottlehead Crack and stumbled across a small problem.

I went through the resistance checks and everything seems fine except for terminal 20. The crack manual states I should be getting 0 Ohms but mine reads 10.13M Ohms.

I'm using a UNI-T UT33C multi-meter and resistance settings are (200; 2000; 20k; 200k; 20M ohms)

Here are my readings:

Terminal & Resistance

1 *
2 *
3 0 ohms
4 *
5 *
6 2.48k ohms
7 2.85k ohms
8 0 ohms
9 2.95k ohms
10 2.48k ohms
12 0 ohms
13 fluctuates
14 0 ohms
20 10.13M ohms 
22 0 ohms (btw I followed the revised manual and soldered blackwire from terminal 4 of the transformer to terminal 14U instead of 22L)
B3 2.94k ohms
B6 2.94k ohms
RCA Ground lug 0 ohms
Center pin 110k ohms

I double checked the resisters 4x (UF4007 rectifiers) and they are in the correct orientation. The filter capacitor on terminals 20U and 21U with the strip side on terminal 20U.

Do I have to resolder everything in terminal 20?

TIA

[Grainger49]

Ok, you have the right reading on terminal 12 and 14.  They should be tied to terminal 20 with a black wire jumper that crosses the transformer from terminal 14 to terminal 20.  That is the last 2 steps on page 28 that I have.  It might be missing or mis-soldered.

Nice catch.

[lordnikon]

I reheated the joints and magically everything is within spec. Terminal 20 reads 0 ohms. Now onwards to voltage checks.

[lordnikon]

Plugged in the unit and the tubes light up. However, the readings are nowhere near the voltage ranges in the manual and also the readings are negative values. 

Also, only one red LED is illuminated for the 12AU7 socket. The other doesn't. Is that normal? What does it indicate anyway?
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fs1.postimg.org%2F8h5wp25y3%2FCrack.jpg&hash=08844a22d2710296c7d54ff6e2232831fc4e1dbc)

The readings so far:

Terminal & Voltage

1 -133V
2 -148
3 0V
4 -148V
5 -133v
6 -75V

This is with a 240V Transformer.  Mains are 220v AC 50Hz

[Grainger49]

The voltages will be negative if you get the meter leads swapped.  If the black lead is plugged into the common input and the red into the V, Ohm input the black goes on the chassis the red on the terminal you measure.

Verify that the silver banded end of the LED that doesn't light is toward the center pin of the tube socket.

Terminal 6 being at 75V is really odd, but it might have been terminal 7 which is specified at 100V.

Take a full set of voltage readings.  Post those that are 15% or more out of specification.  For instance, 148 is not out of spec.  (Just barely!)

[lordnikon]

You're right I swapped the terminals for the red LED and now it works. All voltages are fine as well.

Terminal and voltage

1 79V
2 155V
3 0V
4 155V
5 81V
6 0V
7 96V
8 0V
9 100V
10 0V
11 0V
12 0V
13 155V
14 0V
15 174V
20 0V
21 194V
A1 80V
A2 0V
A4 0V
A5 0V
A6 77V
A7 0V
A9 0V
B1 77V
B2  154V
B3 96V
B4 80V
B5 154V
B6 99V
B7 0V
B8 0V


One last thing. Plugged it in and it sounds fabulous but no right channel. bummer.

During the resistance check, I noticed the right RCA jack center pin has 0 resistance. The left RCA jack however reads about 100k ohms.

[Paul Birkeland]

During the resistance check, I noticed the right RCA jack center pin has 0 resistance. The left RCA jack however reads about 100k ohms.

Sometimes there can be a metal burr that will allow the outside shell of the RCA jack to touch the center pin.  If you look at the bottom of the jack, there should be a uniform gap that separates these two bits of metal.  If you see a spot that looks suspect, you can separate them with a small nail or small metal pick. 

[lordnikon]

Changed the RCA jack and resoldered it. Now everything works. Sounds awesome with my HD600s. Very happy 

Thanks everyone