Crack build in NJ

[ptempel]

Completed the basic build today.  Was doing the resistance and voltage measurements.  The resistances look ok to me.  The voltages differ a bit from the recommended values, however.  The second number was in the manual and the third number is my measurement.  Let me know what you think.  Will go back over the schematic and build steps for now.

Terminal  Resistance (ohms)
3  0  0.4
6  2.4K  2.492K
7  2.9K  2.953K
8  0  0.6
9  2.9K  2.933K
10  2.4K  2.491K
12  0  0.5
14  0  0
20  0  0.6
22  0  0.5
B3  2.9K  2.953K
B6  2.9K  2.933K
RCA jacks:
Ground lug  0  0.6
Center pin  90K

[Grainger49]

Philippe,

To help you interpret the meter readings you should read question #7 on the FAQ Thread.

The easiest way for you to get any problems straightened out is to post only the voltages that are more than 15% out of spec.  It is easy to edit your post above, use "Modify".

I agree none of your resistance measurements are more than a percent or two out of spec.  Your voltages on T1, T2, T4, T13, T15, T21 are all high.  This is seen often when a tube is not conducting.  Just guessing, I'm not looking at the schematic, but only one half of your driver tube is conducting (technical for working) and neither side of the output tube is working.  The problem is often in the cathode circuit of the tube. 

You are not alone, and it can be fixed through the forum here.  I'm headed to bed but will be up early tomorrow.  If no one has given specific advice (I sure haven't) I will wade in then.

Have faith!

[Paul Birkeland]

Hello Phillipe,

It looks like one side of your 12AU7 isn't conducting all the way.  Can you see two glowing spots on the top of the 12AU7? 

[ptempel]

If I look closely, I do see two small glowing spots at the top of the 12AU7 tube.  Have to tilt the amp upward to see them under the silvered top.  I also see the two LEDs glow under the tube socket.  Just to cover all the bases, I ordered replacement tubes online.  I don't have a headphone to test with yet.  Have one on order and trying to find the 1/4" converter for the Supralux.

EDIT: Tested with the headphone adapter and heard no sound from the amp yet.  Will wait for the replacement tubes to retest.

[Grainger49]

I have the feeling that with 218V several places you expect 90 or 170 that the output tube is not turning on either. 

[ptempel]

Ok thanks Grainger.  Will send an update after I receive the replacement tubes.  Am getting excited to listen to the Crack!  Bought a used pair of Sennheiser HD600 headphones as well.

[Sh7eleven]

I also picked up a pair of used hd-600's for use with the crack, its a great pairing and a pretty good bargain too.

[Grainger49]

I am going to have to run out for an AC repair.  But I have the schematic out and with 218V on tube pin A6 (plate) the tube is not conducting.  This means the LED from tube pin A8 to ground should be out.  But you say it isn't.  Odd, really odd.

The plates on the 6080, tube pins B2 and B5, are both at 218V.  That means that the tube is not conducting on either channel.  The 3k resistors (really big ones down the center of the chassis) from T7 (tube pin B3) to T3 and T9 (tube pin B6) to T3 are what control this.  Since T3 is the chassis ground it is unlikely it is a problem, but check the solder joint to the resistor leads.  The problem most like is between the tube pins to the terminal strips. 

Measure resistance from tube pin 3 to terminal 3.  You should read 3k ohms. 

Measure resistance from tube pin 6 to terminal 3.  You should read 3k ohms.

Otherwise I guess it is the tubes.

[ptempel]

I also picked up a pair of used hd-600's for use with the crack, its a great pairing and a pretty good bargain too.

Agreed.  It beats $400+ for the HD650.  Also read that some prefer the HD600 to the 650 anyway.

[ptempel]

Measure resistance from tube pin 3 to terminal 3.  You should read 3k ohms.  
Measure resistance from tube pin 6 to terminal 3.  You should read 3k ohms.

Otherwise I guess it is the tubes.

Ok, will do when I get home.  6080 pin3 to termimal 3: 2.953K ohms.  6080 pin 6 to terminal 3: 2.932K ohms.  So they look ok to me.

[ptempel]

I received the Sennheiser HD600 headphones.  They sound great (tested with older receiver).  Still waiting for the replacement tubes.

[ptempel]

Took delivery on the replacement tubes today.  Just plugged them in and...   nothing.  So my issue is somewhere else, unfortunately.    I noticed that there is a 270K ohm 1 watt resister in the B+ PS schematic and in some photos.  This didn't come in the kit as far as I can tell.  Do I need it?

[Jim R.]

Phillipe,

Yes, the 270k is the bleeder resistor -- mainly their for safety purposes.  Now, if it's the 270 ohm power resistor that is missing, then yes, you have a problem, but that should have made itself known a while ago.

Definitely get the bleeder in there, especially if you're going to do any more work under the hood.

I'm still betting the noise is from the impedance of the headphones and/or tube break-in.

BTW, tell me about your usb isolator when you get a chance.

Thanks,

Jim

[Paul Joppa]

Yes you need it. It's purpose is to discharge the capacitors so that it is safe to work on the inside. The instructions for installing it are on page 30. Didn't check that one off?  :^)

Somewhere there are instructions for making a fast discharger, usually a 10K resistor plus clipleads, and how to use it. You'll want to do that before exploring the insides!

[Grainger49]

There are two 270 ohm (not k ohm) resistors in the power supply.  The 270k ohm resistor is called the bleeder resistor.  It gets rid of the voltage quickly when you turn the amp off.  It is installed on page 30, the last instruction on the page.

As I said above, I believe your problem is in the cathode of three of your tubes. 

Check the 12AU7 pins 3 and 8.  There should be an HLMP 6000 LED there and they should light up.  From your voltage readings, A6 has 218V and A9 has 1.5V.  That doesn't make sense.  Check the 22,100 ohm resistor connected to A6.  Is that the right resistance?  Just measure across it.

The same thing goes for B2 and B5.  There is too much voltage there for you having the right cathode resistor.  Since the resistance measures right it might not be properly soldered in/grounded.  Check from the tube pins to the chassis plate, leave out the terminals that the resistors are soldered to.