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PostPosted: Sun Apr 16, 2017 8:04 pm 
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coco wrote:
Disconnect all the wires from the circuit, then use a digital ohm meter to measure the following resistances.


OK, I assumed you meant disconnect the OT wires, which I did. I did not check the blue/white or brown/white wires because they are tied and heatshrink closed outside of the chassis. The other readings came out close to what you indicated:
Primary
Brown - Red: 271 ohms
Blue - Red: 326 ohms
Brown - Blue: 600 ohms
Brown/White - Blue/White: 326 ohms

Secondary
Black - Orange: 1.0 ohms
Black - Green: 0.8 ohms
Black - Yellow: 0.6 ohms

While the rotary switch was disconnected, I checked continuity on the switch terminals. I assume that the switch toggles connections between the different OT wires and the "hot" wire. The switch shows continuity between the 4 Ohm terminal and the hot wire when 4 Ohms is selected. There is no continuity at the 8 and 16 ohm terminals when those are selected. Doesn't that mean the switch is bad?

Should I run the amp with the 8 ohm wire directly connected to the "hot" wire? I imagine that if that works, we can assume that the OT is ok, and the switch is bad. But I'd like you to confirm that this is safe before I proceed. Thanks, CR


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PostPosted: Mon Apr 17, 2017 3:10 am 
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Joined: Sat Dec 04, 2010 3:42 pm
Posts: 519
Location: Qualicum Beach, BC
Yes, that's what Stephen meant when he said to disconnect the wires and measure the resistance.

I thought we did that a few days ago and it was good. I also thought we checked the switch itself for continuity at all positions and it was good.

Your idea of connecting the 8 ohm wire directly to the hot terminal of the jack is a good one. That was going to be my next suggestion.

You said the ticking stops if you pull out V3. That's the phase inverter that drives the power tubes. Is the ticking still there if you just pull out both V4 and V5?


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PostPosted: Mon Apr 17, 2017 11:04 am 
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Problem solved!

It looks like the switch is bad because when I soldered a jumper from the 8 ohm switch contact to the red contact, it worked. (a clip jumper from 16 ohm to hot also worked). Stephen said that he'd send a replacement so that should get sorted soon.

I also found the source of the ticking--I have a thing called powerline internet that runs internet signals through the power lines in the house. I unplugged it, and the ticking went away.

The amp sounds absolutely awesome now! Thank you for your help!


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PostPosted: Mon Apr 17, 2017 5:26 pm 
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Location: Qualicum Beach, BC
Glad you found the problems and the amp is sounding good. Yes, I kind of figured the ticking problem was noise on the power line which is why I suggested checking that last week.

Hope you enjoy your amp and the experience of building and trouble shooting it. It's nice when they work the first time, but you learn more if you have to fix them.


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PostPosted: Tue Apr 18, 2017 5:21 pm 
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