Crack voltage question

[BillWay]

Got it together, all resistances check out.

Your instructions say to connect the neg probe to terminal 12... then, without checking anything at all, to reconnect it to the ground bus -- I assume that means terminal 16 or the bare wire coming off that.

Voltages are fine up to A3. Then A4 and A5 are at 180 VDC -- not 0 VDC -- and so of course is B8. That's a little warm for a heater!

My heater wires are:
red: xfmr 4 to B8, A4, and A5
blk: xfmr 5 to B7, A9

Your voltage checks for all heater connections say 0 VDC. I'm obviously a tad confused.

WW

[Doc B.]

Ground = ground buss= terminal 12, and that is where the black test lead should connect. T16 is chassis safety ground. Black to that can give a wrong reading.

[BillWay]

With the neg on terminal 12, here are my voltages:
T1: 90
T2: 168
T3: 0
T4: 168
T5: 83
T6:0
T7: 105
T8: 0
T9: 103
T10: 0
T11: 0
T12: 0
T13: 168
T14: 0
T15: 189
T20: 0
T21: 210

A1: 82
A2: 0
A3: 1.54
A4: 180
A5: 180
A6: 80
A7: 0
A8: 1.54
A9: 188

With the heaters so high, I didn't leave it on to check B1 to B6. B8 is of course also at 180.

I had a friend go through each connection and check them off - he didn't find anything wrong. (Obviously, there's *something*...)

Suggestions?

WW

[BillWay]

One more note - there is something inside the 6080 that's loose and kicking around inside the tube. In the pic, it's to the right against the dark background - it's a little piece of clear material that's free to move all around inside.

[BillWay]

forgot to add the pic - it's attached.

[Paul Birkeland]

There is a jumper from transformer terminal 4 or 5 to the ground buss in the power supply.  Your jumper is connected to the B+ (which is why you have 180V-DC) and not the ground.  I'm sure if you check that particular wire against the drawing/instructions, you will find your error.

[nsorens]

I also got these high readings with my build of this kit.  Page 19 of the revised (4/26) building instructions have a red note saying that "for more quiet operation, connect a 3" black wire from power transformer terminal 4 to terminal 15U instead of 22L".   Would this be causing the high readings?

[Doc B.]

Here is a link to the corrections to the manual we posted after the first kits shipped:

http://www.bottlehead.com/smf/index.php/topic,657.0.html

The little piece of glass inside the tube envelope is a fairly common occurrence and does not affect its performance.

[BillWay]

NSORENS is right: the 4/26 revision to the instructions, printed in red on page 19, to run a black wire from xfmr #4 to terminal 15U is wrong. Run the black from xfmr #4 to 22L, or to #12, which it too crowded, or to #14 (which is what I suspect they meant to say.) It does seem a tad quieter with that lead on #14.

Terminal 15 has the B+ voltage on it, and will kill you heater wires in very short order.

The Crack now making some pretty lovely music, and, as I suspected, the Senn HD800s are heaven with it.

WW

[Doc B.]

Arrgh. Thanks Bill, I will correct the corrected correction...

The current, correct version of the Crack manual is now version 5/6/10. The corrections to previous manuals are described at this link:

http://www.bottlehead.com/smf/index.php/topic,657.0.html

[nsorens]

Duh-O,
I was checking my voltages after making this wiring correction (everything was checking out perfectly) and slipped with the probe, bridging the A8 and A9 terminals for a second.  Now I have a dead LED and 11.5V at A8 instead of 1.5V.  Will a new LED get me back in shape or is there a chance of further damage?

[ironbut]

You know, there just aren't that many components in this amp which should make troubleshooting a snap.
Actually, I tried using a Brimar 13D5 that I got a while ago for cheap from that auction site. It turned out to have a short in one half. I saw a tiny flash and heard a faint snap and the left channel was dead. I circle filed the tube and replaced it with a known good one, fired up the amp and looked underneath. Sure enough, the led for that channel was dark.
I took a look at the resistors in that channel and none looked cooked. I checked the diode and it was done. Luckily, I had some on hand and 15 minutes later, the amp was making sweet music again.
Easy Breezy and cheaper than a fuse!

[Paul Birkeland]

Duh-O,
I was checking my voltages after making this wiring correction (everything was checking out perfectly) and slipped with the probe, bridging the A8 and A9 terminals for a second.  Now I have a dead LED and 11.5V at A8 instead of 1.5V.  Will a new LED get me back in shape or is there a chance of further damage?

Yes, call Bottlehead and they will mail you a new LED.  (maybe even two)  Nothing else should be damaged, the parts in this kit are quite robust!

[nsorens]

Called Eileen and parts are on the way.  Thanks Bottlehead crew!

[Paul Birkeland]

If you are absolutely nuts about waiting for the LED, here is how you can calculate an appropriate resistor to put in it's place:

measure the voltage difference across the plate load resistor that feeds the side with the burnt out LED (the plate load resistors are between terminals 1 and 2 or 4 and 5).  Now measure the actual resistance of that plate load resistor (with the power off).

Now, using V=I*R, you have a value for V and a value for R.  Solve for I (should be .00something). 

The LED makes 1.57V under the cathode, so you now know I and V for another V=I*R equation, so
1.57=R*I where R will be your cathode resistor in ohms and I is the current value you calculated above. 


I *could* just grab my Crack and do all this for you, but that isn't in the spirit of DIY!