Vox AC30 C2 Drops Dead

[The New Steve H]

A buddy of mine has a Vox AC30 C2 with a solid state rectifier. One of his power tubes blew up. The tubes have been replaced, but he says there is no sound. They say "the fuse" (meaning one) is good. I don't know if there is another one in there, or maybe a resistor that is intended to fry. I don't have the amp in front of me. Any ideas?

[Firestorm]

Two fuses, I believe. Have him check both.

[Zippy]

A buddy of mine has a Vox AC30 C2 with a solid state rectifier. One of his power tubes blew up. The tubes have been replaced, but he says there is no sound. They say "the fuse" (meaning one) is good. I don't know if there is another one in there, or maybe a resistor that is intended to fry. I don't have the amp in front of me. Any ideas?

Any ideas? You bet!

Open it up and take a look. If it's another fuse - find it and be a hero. If it's a smoked resistor, you should see it real easy. If none of the above, it's an excellent opportunity to learn to troubleshoot. You already know it's limited to the output section so half your work is done.

Enjoy!

[The New Steve H]

They found the other fuse on the PCB board, and it was fried. I'm guessing the power tube that exploded shorted and killed the fuse. I have sent them to Radio Shack.

[Cliff Schecht]

I've serviced a few of these amps. They are true pieces of shit in my opinions, both in design and execution. The quality of the components and the build quality are typical Chinese junk but these amps are an extra pain in the ass to work on. To change tubes you have to remove at least 30 screws, if not more, and will find yourself straining to get to some of the recessed screws.

The last one that I repaired had solder melted off of the rectifier socket. I don't know how it got hot enough to melt but I fixed this, replaced the rectifier and power tubes and it came back to life.

In this one it sounds like a dead resistor or fuse like others suggested. Has your buddy plugged in the preamp out into another power amp to verify that the pre is still working? I'm guessing he hasn't taken any voltages yet..

Also as you may or may not have heard these amps are notorious for arcing tube rectifiers if you use the standby switch. Recommend to him that he doesn't ever flip the standby switch off, or take this one step further and short the switch to permanently on.

[tubeswell]

Another 'fix' for the standby is to convert the standby to a 'soft start' switch, whereby you wire a 150k-220k 1W resistor permanently across the switch, and this limits inrush-current surge when you turn the main power on, and it lets the B+ rail rise to 40-50V or so. Then when you flip the soft-start/stdby switch on, the B+ goes the rest of the way to full power.

Also wise to add SS diode protection in series with the HT winding and rectifier tube's anodes in tube-rectified amps