Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: ptempel on July 28, 2012, 11:38:22 AM
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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
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Philippe,
To help you interpret the meter readings you should read question #7 on the FAQ Thread (http://bottlehead.com/smf/index.php/topic,2408.0.html).
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!
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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?
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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.
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I have the feeling that with 218V several places you expect 90 or 170 that the output tube is not turning on either.
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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.
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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.
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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.
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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.
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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.
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I received the Sennheiser HD600 headphones. They sound great (tested with older receiver). Still waiting for the replacement tubes.
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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?
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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
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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!
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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.
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BTW, tell me about your usb isolator when you get a chance.
I bought it populated from circuits@home:
http://www.circuitsathome.com/products-page/usb-interfaces/adum4160-usb-isolator-board-populated
I forget where I learned about it (DAC thread maybe?). But it does seem to clean up the dirty power from the computer by decoupling it. Only drawback is that you need another outlet for the 5V power supply for it. I only have a cheap wall wart from Radio Shack. Maybe a linear 5V PS or battery would be better.
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Thanks all for the help and advice. Will replace the bleeder resister first this weekend before troubleshooting further.
EDIT: Tried to get the resistor at Radio Shack but they only had the 1/2 watt version. So sent a mail to Eileen ([email protected]) and requested it from her.
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Got a note from Eileen and will be getting the resistor soon. A quick question about it. The only purpose for the 270K 1 watt resistor is to discharge the caps. Correct? If so, then my problem may lie elsewhere but should wait to put this in.
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Phillipe,
That is correct -- install the resistor before doing any more work under the hood. And best to leave the amp off between now and then and it may even be advisable to build a cap discharger as was mentioned earlier.
And also correct that this resistor probably has nothing to do with the other problem, but once it's a bit more safe under there we can get back to figuring that all out.
Thanks also for the info on the usb isolator -- definitely going to check that out.
Where in NJ are you -- grew up there and lived there a good portion of my life.
-- Jim
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Phillipe,
That is correct -- install the resistor before doing any more work under the hood. And best to leave the amp off between now and then and it may even be advisable to build a cap discharger as was mentioned earlier.
And also correct that this resistor probably has nothing to do with the other problem, but once it's a bit more safe under there we can get back to figuring that all out.
Thanks also for the info on the usb isolator -- definitely going to check that out.
Where in NJ are you -- grew up there and lived there a good portion of my life.
Ok, thanks Jim. Let me know what you think if you get the USB isolator. Its a small difference, but its cheap so I thought why not give it a go. I'm in Bloomfield, NJ. My place is only three blocks from where I grew up since 1978. So I've been in the hood for a while. :)
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Phillippe,
I'm old, I can't make out your avatar. What is it? Maybe post the picture in a larger size? I see a cat but can't make out the head or what is in its lap. If you say it is another animal I'm really going to feel old.
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Philippe,
My last job before I had to retire for disability reasons was in Clifton and while there I lived in Little Falls and Montclair and a lot of my work colleagues had grown up in Bloomfield. Can't say I've ever been there myself though.
I'm originally from the Princeton/Lawrenceville area myself.
-- Jim
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I'm old, I can't make out your avatar. What is it? Maybe post the picture in a larger size? I see a cat but can't make out the head or what is in its lap. If you say it is another animal I'm really going to feel old.
I think its a Nintendo DS (portable game thing). It originally looks like a mini laptop to me so thought it was a funny avatar. Sort of me as a geeky cat I guess. :) I received the 270K resistor on Friday. Just have been a lasy sow and have not installed it yet.
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Philippe,
We need to get the Crack up and running. The forum can walk you through it. I'm still convinced the problem is in the cathode circuits.
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I think it's some Nintendo employee's cat.
http://www.kotaku.com.au/2009/10/so-shigeru-miyamoto-now-has-a-cat/
Never saw the original image before. Got mine from a copy at images.google.com. Forgot what I searched for, but thought it was cute. :-) Learn something almost every day.
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Philippe,
We need to get the Crack up and running. The forum can walk you through it. I'm still convinced the problem is in the cathode circuits.
Sorry for the looong delay in replying. :( We recently have been shuffling around a lot of stuff at home to make way for a new baby boy. Still have the crack and will try to get the bleeder resister in there. Will have to recheck the manual and meditate on the schematic for a bit to see how to check the cathode circuits. I still have the speedball upgrade built and waiting in the parts box. But don't want to touch it until I get my basic build debugged.
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So a 300k resistor would work as a bleeder resistor then? If i put 2 150's in series?
I am in union city and building a crack too. I posted a photo under the topic crack construction. It would be fun to compare the 2 cracks sometime once they are upmand running n broken in.. I also have a couple bottlehead amps n a foreplay. Congrats on the new baby!
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Hi Philippe,
Congratulations on the new addition to the family! Better get that amp going soon -- you're going to need those headphones :-).
Once you get some time and are ready to tackle the troubleshooting again, we'll all be here ready to assist.
-- Jim