Crack;Bottlehead OTL
May 5, 2012 at 2:22 PM Post #1,156 of 11,504

MayorSimpleton

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Yes you can powdercoat both and they will handle the heat. We have done quite a few over the years. Be careful to clean the transformer bell end very thoroughly as it has a sort of oily/sticky coating to keep the raw steel from rusting. Running it in the dishwasher will usually strip it off. 

Lovely - thanks for the tips.  I put my order in today - looking forward to it.
 
N
 
May 10, 2012 at 9:01 PM Post #1,157 of 11,504

Jidonsu

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I just received a used Crack with the Speedball upgrade.  I have some background noise coming through the left channel even with the volume turned down and inputs disconnected. The right channel is silent.  Is this normal?  Thanks.
 
May 10, 2012 at 9:18 PM Post #1,158 of 11,504

BmWr75

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No, it is not normal.
 
Turn the amp off.  Pull both tubes and then reinstall them.  It is a long shot, but easy to try.
 
May 10, 2012 at 9:44 PM Post #1,159 of 11,504

Jidonsu

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Thanks.  I tried that. No luck.  I tried cleaning the pins on the output tube a bit, no luck there either.  Get new tubes? Haha. 
 
This is my first tube amp, so I'm not completely familiar with how it works.  After powering on, the the left channels comes through first after a few seconds, followed by the right channel a couple seconds after that. 
 
May 10, 2012 at 11:24 PM Post #1,161 of 11,504

liamstrain

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what kind of background noise? 
 
hiss? or hum?
 
May 10, 2012 at 11:54 PM Post #1,162 of 11,504

Jidonsu

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It's a hiss, like white noise.  I read on the Bottlehead forum that it can happen with some tubes, especially if the tubes are fairly new.  I ordered some 6AS7G to replace the 6080.  If that helps, great.  If not, we'll see. 
 
 
May 11, 2012 at 12:33 AM Post #1,163 of 11,504

liamstrain

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That is true - the tubes need some time for the cathodes to form up... and the hiss *should* decrease. If you are getting it in one channel and not the other - it is possible that you have a tube that is in not great shape, and one triode is uneven. 
 
May 11, 2012 at 6:51 AM Post #1,164 of 11,504

BmWr75

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Not really related, but with tube amps it's best to leave the headphones unplugged for 30 seconds or so while the amp warms up.

 
Really????  I can think of no reason this would be advantageous.  Letting the amp warm up with the cans connected and the volume turned down is probably better for the amp.  Many folks say a tube amp should never be powered up with no load on it.......this is probably an old wives tale though.
 
May 11, 2012 at 7:23 AM Post #1,166 of 11,504

Beefy

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Really????  I can think of no reason this would be advantageous.  Letting the amp warm up with the cans connected and the volume turned down is probably better for the amp.  Many folks say a tube amp should never be powered up with no load on it.......this is probably an old wives tale though.

 
Just because you can't think of reasons doesn't mean there are none. OTL amps can have large spikes of DC when the tubes start conducting. With low impedance phones it dissipates quickly but it can translate into a pretty high current.
 
And the amp does have a load even with no phones connected; a couple of resistors. These bleed away the DC if no phones are connected.
 
May 11, 2012 at 1:37 PM Post #1,167 of 11,504

BmWr75

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I admit that me being wrong is a very real possibility. 
 
Maybe Doc from Bottlehead with chime in with some facts.
 
May 11, 2012 at 2:18 PM Post #1,168 of 11,504

Beefy

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I admit that me being wrong is a very real possibility. 
 
Maybe Doc from Bottlehead with chime in with some facts.

 
It isn't a possibility, and Doc's input is not required - you are wrong.
 
May 11, 2012 at 2:34 PM Post #1,169 of 11,504

Doc B.

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I don't think any of this is reason enough to get feathers ruffled. None of our gear needs to be connected to a load to run. There is a bit of DC offset at startup of a Crack, which is why we have a bleeder resistor across the output. It's probably not necessary in the  majority of situations (and honestly I forget sometimes myself), but we do recommend waiting to plug in headphones until after the amp has warmed up for 30 seconds or so.
 
May 11, 2012 at 2:54 PM Post #1,170 of 11,504

BmWr75

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Thanks for the clarification Doc B.  I had never hear this before and have always had my HPs plugged in when turning the Crack on.  It has never caused any problems that I'm aware of so far.  Most of my HPs are 600 ohm that I use with the Crack.  Will try to remember this in the future.
 
I have 4-5 other tube amps I use with headphones, all with output transformers though, and have always kept the HPs plugged into them to as they are powered on and off.  That was the basis for my original response to the question.
 

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