SWR Workingman's 15

[AtomicMassUnit]

With no speaker attached, I can turn it on with my light bulb limiter and the light doesn't come on. With a speaker attached, it does. My bench speaker is good btw. The outputs aren't shorted according to diode test on my meter. What could it be?

[52 Bill]

Some SWR amps will not power up correctly with a light bulb limiter.

What did you fix, or what was wrong with the amp? If you power up directly from the ac line, with no speaker is there dc on the speaker out?

[AtomicMassUnit]

Nope, no DC on the speaker jack.

The fuse on the power amp board was blown, so I guessed the outputs were gone. I removed them and powered up with the limiter, it didn't glow, so I measured the transistors with the diode tester, they read correct on that, and I put them back in, no load, powered up with limiter, it didn't glow, then attached speaker, and it did.

[AtomicMassUnit]

Interesting development. It started working. I think this has something to do with the switch on the front that switches tweeter/headphones/full range. If I power the amp on in the full range setting, the limiter comes on. If I power it up in either of the other settings, then switch to full range, it works fine. Hmm...

So, for some reason, if the horn is engaged when I turn it on, the amp draws excessive current, but if I engage it after, it's fine. Does that indicate the switch or should I look at the horn itself or crossover?

Also, the fuses in this amp solder directly to the board. What's the deal with that?

[AtomicMassUnit]

Ok, I replaced the switch. That's not it. I removed the tweeter, that's not it. It can't be the woofer because in the 'horn off' setting, it's only the woofer and it powers up fine like that. It's only when the amp is fired up in the full range setting that it does this. If I switch to full range after it's on, it works fine. What is going on here?

[Enzo]

But what exactly does the amp do when plugged directly into the wall now? No bulb limiter?

[AtomicMassUnit]

Aha! Plugged into the wall with no limiter, it works. Why is that?

[Enzo]

The bulb limiter is intended to protect the circuit and indicate problems, when amps draw excess current. It is not intended to work invisibly with the amp. The resistance of the bulb is in series with the amp circuits, so it affects voltages at the very least. It may also interfere with the power on delay circuit of the power amp. Once you have determined that the amp is not going to blow its fuse, get rid of the bulb.