Monday, 21 February 2011

Tube glow

Everything is in the right place. Or at least I hope so, because when I turn this thing on I don't want it to explode or electrocute me.

We need to turn the circuit on in stages, so we can identify where a potential problem might lie. Or at least that's the theory.

First up we plug it in with no tubes at all. This exercises just the first part of the circuit. I was pretty edgy plugging this thing in to the mains. I think it's because the chassis is made of metal, and metal conducts electricity. All 110 volts of it.

So I gingerly plugged it in and then nervously turned the volume knob to switch the amp on. The power lamp glowed a satisfying red, the fuse didn't blow, nothing went bang or started to smoke. So far so good.

Next up I had to insert the 5Y3 tube and repeat the exercise. Again nothing went pop.

No it's the turn of the 6V6 tube to get warmed up. I also had to connect the speaker at this point, as the load it provides is important to prevent the amp burning out. Still no smoke. And no ominous sounds from the speaker.

Lastly I put the final 12AX7 tube in and inspect once more. Still nothing to suggest we had any problems. Could it be that I got it right first time?

So I turn off the amp, plug in the guitar, and turn it on again.



Damn. Looks like there's a hard to find gremlin lurking in there after all. How on earth am I going to find it?

But then, about 10 seconds after turning it on, the sound of the guitar starts to build in the speaker. Everything is fine after all, it just takes a little while for the circuit to warm up!

The tubes glow with a very satisfying orange, and this thing can sing! The sound is really warm and fat, and makes my '66 Jaguar sound awesome. Even my cheapo guitar sounds good.

It's loud, too. I'm not sure my neighbours really appreciate the riffing as I take it through its paces.

I haven't put the back on the amp just yet. It's much more fun to be able to see the guts of the thing. Just got to be careful not to put any fingers inside!

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