HT1R cracking sound

[ghossand]

I recently bought myself a blackstar HT1R combo and I noticed that one minute after I turn the amp on, it will produce a cracking sound for about 2 minutes. I have zero experience with electronics so I was wondering if someone here knows what could be the issue with the amp and if it can be fixed.

[thephantum]

A crackling sound is usually caused by arcing...or electricity finding a path to ground that it shouldn't normally have. There could be any number of things causing it. Since it goes away after a few minutes there's a strong possibility that there's a bad solder joint someplace. When the amp is cold, the joint is loose and arcing occurs...but once the amp heats up things expand just a little and the solder becomes just a little softer....so the arcing stops.

However, it's most likely one of the tubes. The HT-1 is cathode biased, so you can change the tubes without having to manually bias it. Keep in mind that if the amp is under warranty, you will void it just by removing the back panel....much less changing tubes.

Towards that end, if the amp is brand new, take it back and get another. If it's still under warranty, take it to an authorized service center.

[ghossand]

Unfortunately it's not under warranty anymore. I've read that changing the tubes can be easily done by myself, but for the soldering part I would have to ask someone else. How easy would you say it is to find the spot where the solder has failed? And what tube shall I use to replace the old one? I read the amp has a sovtek 12ax7 tube now, is that the best one to put back into or shall I use another one?

[thephantum]

If it's not a tube, it should really go to a tech. Sometimes you can spot where solder has failed (or has a dry joint) very easily. Other times, it takes a signal generator and oscilloscope to find it. The problem is that even when powered down and unplugged, tube amps can store lethal voltages in the filter capacitors. So unless you know how to safely discharge them, it's best left to someone who knows what they are doing.

Having said all that, based on the fact that the amp is 2+ years old (out of warranty), I strongly suspect new tubes will solve the problem...so I would just replace both. The preamp tube is a 12AX7. The power tube is a 12AU7. I would replace them with Tungsol's. Both are relatively inexpensive.

FYI - They will look almost identical, so don't just pull both tubes out. Pull only one, look at the writing and identify it, then replace it with the correct type. Then do the same with the 2nd tube.