Friday, 31 May 2013

Power up

There's only so much testing you can do before you have to bite the bullet and plug it in. 

There are some detailed test plans but frankly, I couldn't be bothered with all that.  I was keen to see if my amp worked.  I did at least take the precaution of powering up for the first time with no valves.

All OK.

Added all valves, powered main switch.

All valves glowing nicely.  Waited a couple of minutes.

Moved standby switch to "on".

HUGE HUM.

After powering down and unplugging the amp I put it back on the bench and looked for any wiring problems.  After about two minutes of staring I saw what I'd missed - the ground wire for the cap can wasn't connected to the star ground, it was just curled under the turret board.  Whoops!  Stripped, tinned and soldered then time for a retest.

NO HUM.

Right.  Time for the signal test.  Plugged guitar into normal channel, edged up volume carefully...

NO OUTPUT.

Bollocks.  No time for any further investigation so powered down amp.  Paranoia sets in.  Could be a dodgy valve (can be eliminated by swapping them round) or could be something more serious - like the most expensive component of the amp, the output transformer, which can't even be replaced as the boutique maker doesn't make them anymore...

No comments:

Post a comment