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Crack;Bottlehead OTL
Mar 3, 2015 at 10:12 AM Post #6,571 of 12,335

Well, I'm no electrical engineer and I'm sure there are those better qualified to answer your question.
 
You will get hum from your amp when there is no source connected to the inputs.  I believe the reason for that is that those connectors are un-terminated until a source is plugged into them.  As soon as you plug a source in, the hum should disappear.
 
Someone correct me if I'm wrong.
 
You should visit the forums on Bottlehead's website.  They're really good about answering technical questions quickly and concisely.  Very helpful folks over there.
 
Mar 3, 2015 at 7:36 PM Post #6,572 of 12,335
utopia said:
   
I tried different cables and got different results - more or less buzzing at 90 % with different cables. Then I remembered reading over at Bottlehead's forum about shorting the inputs, as part of the troubleshooting process, and when I tried that the amp was absolutely quiet. I think that means the amp itself is ok.
 
Still I get noise even with nothing plugged in. Does that mean that the RCA inputs themselves are picking up noise?
Click to expand...


Hi there, I had the same fear after completing my build.  Nothing is wrong with your Crack IMO.  On another forum I read that if the inputs are  high impedance, this leads to a hum when nothing is connected.  To solve the issue, just make sure that your source is connected.  Hope that helps!
 
Mar 4, 2015 at 2:38 AM Post #6,573 of 12,335
I have a Crack with Speedball upgrade and the stock tubes, but am looking to change those out for a group that will work well with an HD 650 and a group that will work well with an HD 800. Obviously, we have very drastic differences in signatures here, so I'd expect I'll need separate tubes. What would your suggestions be?
 
Mar 4, 2015 at 3:32 AM Post #6,574 of 12,335
roguegeek said:
I have a Crack with Speedball upgrade and the stock tubes, but am looking to change those out for a group that will work well with an HD 650 and a group that will work well with an HD 800. Obviously, we have very drastic differences in signatures here, so I'd expect I'll need separate tubes. What would your suggestions be?
Click to expand...

 
 
If deep pockets driver tubes GEC 6as7g for a little less Tung-sol 5998 best bang for the buck GEC 6080 and Mullard 6080 imo
Input tube Mullard & Tung-sol 12au7 and Tungsram E80cc
 
Plenty of info here in Nick Tams excellent Crack tube review.
 
http://the-key.enix.org/~krystal/review-tube-bottlehead.html
 
Mar 4, 2015 at 1:27 PM Post #6,575 of 12,335
Mar 4, 2015 at 2:29 PM Post #6,576 of 12,335
What do people think about the Orange Globes in the input? I have a couple left over after selling my Lyr.
 
Mar 5, 2015 at 10:46 AM Post #6,578 of 12,335
chicken steve said:
  Are there any advantages/disadvantages of using the 240VAC power transformer vs 140VAC mains? Which one is the most preferred option?
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There´s the huge advantage that the Crack will work and not starting to smoke when you match the transformer to the voltage that comes out of your wall.
That could be as well your first exercise in getting ready to build your crack: get yourself a multimeter and measure the voltage in your wall socket.
 
Mar 5, 2015 at 9:45 PM Post #6,579 of 12,335
roguegeek said:
  What do people think about the Orange Globes in the input? I have a couple left over after selling my Lyr.
Click to expand...

 
People should think that is the wrong 9-pin triode to stick in your Crack. Uh... that sounded rude...
 
Seriously. I haven't tried it, but dropping a 6dj8/6922 into a socket wired for a 12AU7 is very likely a badideaTM
 
Mar 5, 2015 at 9:55 PM Post #6,580 of 12,335
Wow. 240V transformer on 110V mains. A 6DJ8 into a 12AU7 socket... were on a roll tonight.  
 
Before anyone asks, no - you can't use your amp in the bathtub.
 
And if I sound like an ass, well this should diffuse that notion... I know first hand that you should not let your thumb drift near the amp's mains socket even though it is switched off. If is plugged in... its freakin' plugged in!
 
Mar 6, 2015 at 11:07 AM Post #6,584 of 12,335
Sorry all. I didn't meant to sound cranky. I'm actually just concerned. 
 
With the community what it is, cheap DIY kits like the Crack are falling into the hands of just about anyone. While the instructions give good warning about safety, we all know what happens when enough people are allowed to handle dangerous items. Even cautious people with experience occasionally make mistakes.  My preference would be for the un-initiated to start with low voltage circuits, as they do for good reason in high school or college basic electronics courses.
 
I supposed this is an open forum and questions no matter how innocent should be encouraged.  My bad. My comments were uncalled for and as a former member of the instructor/teaching community I should know better. 
 
 
... and after looking up the pinouts with this excellent resource, I've started to raise my own questions regarding pin-outs. They are very similar:  http://www.bustedgear.com/res_Tube_pinouts.pdf
 
But I believe the voltage and current differ significantly enough between the two tubes that the transformer windings in the crack will overdraw and smoke if you were to drop in a 6dj8/6922/ecc88 type.
 
Mar 7, 2015 at 7:43 PM Post #6,585 of 12,335
Phew! Finally made it through all 439 pages of this megathread. I've been loving my Crack w/ Speedball, and after reading through all of this and learning a ton, I've ordered an assortment of caps to try out, along with some other goodies.
 
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