So I built a HIWATT clone that has been performing beautifully for the last few weeks.
Last night, I was playing at relatively low volume when I head a small "tick" and it just cut out completely.
No hiss...nada...
No fuses blown, no smoke, indicator light is on, cathode current shows normal bias etc.
Any ideas before I remove the chassis and start poking around?
New build just died
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Stevem
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Re: New build just died
If you plug headphones into a speaker jack do you hear anything?
If not then start resistance checking the OT as it may have gone open.
Even when they go the other way and short out I have always heard some small level of audio passing thru out to headphones.
If this is the case you can further prove that out by measuring the AC drive voltage coming into pin 5 on each output tube when you play or better yet drive the amp with a 150mv audio signal.
Another way to prove out this problem is to view the output tubes in a dark room.
If there being driven by an audio signal they will glow up brighter inside there plate structure.
Report back on what you find please.
If not then start resistance checking the OT as it may have gone open.
Even when they go the other way and short out I have always heard some small level of audio passing thru out to headphones.
If this is the case you can further prove that out by measuring the AC drive voltage coming into pin 5 on each output tube when you play or better yet drive the amp with a 150mv audio signal.
Another way to prove out this problem is to view the output tubes in a dark room.
If there being driven by an audio signal they will glow up brighter inside there plate structure.
Report back on what you find please.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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martin manning
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- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: New build just died
If you have normal bias current flowing, about the only other things you can check from the outside are to verify that all of the heaters are functioning, and listen for any sound at all in the speaker like hum or hiss. If those thinks check out you probably have a break or short to ground in the signal path somewhere.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: New build just died
Yup to the above.
It’s also easy to use your voltmeter set for AC and follow the audio output from V1 on down the signal chain .
Should take you more then 5 minutes done this way.
It’s also easy to use your voltmeter set for AC and follow the audio output from V1 on down the signal chain .
Should take you more then 5 minutes done this way.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: New build just died
Turned out to be a bad solder joint on the output jack tab that connects to the impedance selector!
She's up and running great now!
She's up and running great now!
Stevem wrote: ↑Sun Sep 28, 2025 3:03 pm If you plug headphones into a speaker jack do you hear anything?
If not then start resistance checking the OT as it may have gone open.
Even when they go the other way and short out I have always heard some small level of audio passing thru out to headphones.
If this is the case you can further prove that out by measuring the AC drive voltage coming into pin 5 on each output tube when you play or better yet drive the amp with a 150mv audio signal.
Another way to prove out this problem is to view the output tubes in a dark room.
If there being driven by an audio signal they will glow up brighter inside there plate structure.
Report back on what you find please.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: New build just died
It’s good that you found it fast .
Those types of open circuits are what can short out the OT.
A good precaution against that is to place a 250 ohm 5 watt resistor across the output jack.
The amp doesn’t see the 250 ohm resistor unless the speaker circuit goes open.
I would give an eye ball to all the other solder connections while you’re at it.
Soldering jack connections and especially OT secondary wires to them due to there gauge requires a tip of good mass on your iron.
a temp of 650 degrees is where I like mine set to for jobs like that.
Those types of open circuits are what can short out the OT.
A good precaution against that is to place a 250 ohm 5 watt resistor across the output jack.
The amp doesn’t see the 250 ohm resistor unless the speaker circuit goes open.
I would give an eye ball to all the other solder connections while you’re at it.
Soldering jack connections and especially OT secondary wires to them due to there gauge requires a tip of good mass on your iron.
a temp of 650 degrees is where I like mine set to for jobs like that.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: New build just died
Yeah the way I wired it, the wire in question was obscured thus I didn't get a good flow.
What led me to that area was the jack itself read open, yet the tab on the impedance selector that fed the jack read like 4 ohms. Then I started jiggling things around.
What led me to that area was the jack itself read open, yet the tab on the impedance selector that fed the jack read like 4 ohms. Then I started jiggling things around.
Stevem wrote: ↑Sun Sep 28, 2025 8:52 pm It’s good that you found it fast .
Those types of open circuits are what can short out the OT.
A good precaution against that is to place a 250 ohm 5 watt resistor across the output jack.
The amp doesn’t see the 250 ohm resistor unless the speaker circuit goes open.
I would give an eye ball to all the other solder connections while you’re at it.
Soldering jack connections and especially OT secondary wires to them due to there gauge requires a tip of good mass on your iron.
a temp of 650 degrees is where I like mine set to for jobs like that.
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martin manning
- Posts: 14308
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: New build just died
What Steve is referring to re finding it fast, an open secondary will cause very high voltages to appear on the primary and damage to the insulation. I suspect because you were playing at low volume you avoided an expensive repair.
Re: New build just died
Oh absolutely.martin manning wrote: ↑Sun Sep 28, 2025 10:51 pm What Steve is referring to re finding it fast, an open secondary will cause very high voltages to appear on the primary and damage to the insulation. I suspect because you were playing at low volume you avoided an expensive repair.
Mucho relieved when I discovered it was a loose solder joint.