Harbinger One Lamp won't light

[wiseblood]

Hey everyone, I built a Harbinger One and the lamp won't light. I have 15v on both sides of Lamp. Any suggestions of what's wrong? Q13 has 15v on collector and base and emitter vary from about 2.8-3.9

[Govmnt_Lacky]

I have 15v on both sides of Lamp. Any suggestions of what's wrong?

Sounds like you answered your own question bud...

I believe you need GND (or low resistance) on one side of the lamp. It is a DC lamp correct?

[midwayfair]

It's an AC lamp*, but that doesn't mean that both sides should have the same voltage. One leg is connected to 15V DC, and the other leg is connected to the collector of a transistor. Voltage travels to the collector of the amplifier, and the voltage is adjusted to either side of half voltage by the offset trimmer.

The 2015 edition doesn't require the external LED to be connected to function, but the older version did. So if you're using the older version and you didn't hook up your rate LED, you'll have to do that now.

If that doesn't fix it, post voltages on all the transistors in the LFO section, verify that you've tried different settings on the gain and offset trimmers, etc.

*EDIT: On second thought, this is a weird way to put it: It's a light bulb. It lights when voltage passes through and creates resistance on a filament, which produces light, but it blinks because when the LFO voltage swings high, there isn't a voltage difference between the two sides of the lamp. Hope that's clear.

[wiseblood]

Thanks for the reply. The rate Led blinks according to the speed knob position correctly. I will measure and post voltages on Q's in lfo shortly.  Thanks again Jon, and ur response does make sense.

[wiseblood]

Here's the voltages.
Q11- C: 15, B: 5.6-8.5, E: 6.1-10.3
Q12- C: 15, B: 6.2-10.1, E: 5.9-9.6
Q13- C: 15, B: 6, E: 5.5
For some reason the Base and Emitter of Q13 aren't changing now as they were before. Also, I can change the bias V on the Base and Emitter on Q13 w the Offset trim but the Gain trim does nothing. Hope this info sheds some light. I'm now further lost than I was. Ahhh...

[midwayfair]

Here's the voltages.
Q11- C: 15, B: 5.6-8.5, E: 6.1-10.3
Q12- C: 15, B: 6.2-10.1, E: 5.9-9.6
Q13- C: 15, B: 6, E: 5.5
For some reason the Base and Emitter of Q13 aren't changing now as they were before. Also, I can change the bias V on the Base and Emitter on Q13 w the Offset trim but the Gain trim does nothing. Hope this info sheds some light. I'm now further lost than I was. Ahhh...

I think a reflow is in order. That's the first thing I'd do if some  part worked and then stopped working. Q13's emitter definitely seems too high. Double check R47 that you didn't accidentally use a 22K.

[wiseblood]

After a reflow and still no luck I found that the Gain trim pot was bad. Thanks so much Jon. I would've tossed and turned another night if not for your help!
I hope to pay the help forward one day. This thing is a sweet lush sound to my ears.