loud pop in right channel at startup

[magnafuzz]

Had the crack working fine for just over a month now. a couple of quirks seem to have developed overnight.

i turned on the amp today and heard a rather startling crackly-pop come from my headphones when i turned on the amp. It hasnt happened before.

i thought it might be an anomaly so i set aside my good headphones and plugged in some cheapies to give it a listen. everything seems fine except the pop when i turn it on (about a one or two count from when i actually flip the switch).

i noticed that when i give the box a light tap, a little distortion or low crackle comes out of the right channel. would that be due to a microphonic tube or a bad socket? and if it is a bad tube, could that cause the pop at startup? im curious if ive got one or two problems here.

I checked over the circuit and cant find any bad joints or abnormalities. The crack is 100% stock without speedball. Ill go through the resistance/voltage checks again when i get a chance but they checked out when i built it and i havent changed anything.

 

[Laudanum]

I always post this ... get your self a couple spares of each tube type.  12AU7 and 6AS7 or 6080 can both be had for pretty cheap.  They may not be your tubes of choice but they get you by if you have a tube problem and they allow you to troubleshoot a bad tube.  The crackly-pop in one channel can certainly be a tube going south.  It can also be the tube pins or socket contacts causing the crackle when you tap on the cabinet.  Or, a cold solder joint is a common possibility.    Try reseating each tube several times (as Grainger always suggests) which can help clean both pins and socket contacts.  But do yourself a favor and get youself a couple spares of each tube.  It could be something other than a tube or socket but if it's a tube, you need a replacement so may as well have spares on hand.  If not a tube, you can try the "chopstick test", tapping on the solder joints with a wooden chopstick (or small diameter section of wooden dowel or similiar non conductive object)  with amp on and while listening with headphones.  Careful where you put your hands.

 

[magnafuzz]

Thanks for the advice. I went out today and picked up some spares.

I re-checked the voltages and found some of the voltages on one channel had risen upwards of 30% out of spec. Replaced the 12au7 and everything went back within 15%. Hopefully that clears up the startup popping. It hasnt happened the few times ive tested it so its looking hopeful. I was worried it was something more serious than a bad tube... oh well, now i know what to do next time.

 

[Laudanum]

It's Just easiest to check the tubes first whether it's dirty pins or a bad tube.  The good news is that you built it and you can fix it.  The folks here will always help.  So if there is a bigger problem, it will get sorted out.  I've had two bad tubes in Crack myself, one driver and one output tube.  The downside of the risk I take sometimes with ebay and cheap tubes.  Although the output tube was purchased from a dealer and replaced by him.  Point is, it happens.