Popping, Hum, and Heat?

[CapnCook]

Hello,

Newbie, finished build. All tests within specified ranges.

This is my first OTL, so I am not 100% sure what to expect, and I am wondering if these are normal:

1. 'Popping' inserting headphone jack. Loudish, kinda like plugging in an electric guitar.
2. Constant background hum. Volume has no impact. When music is playing, it's mostly imperceptible, but for silent passages.
3. Heat! The headphone jack, when I remove it,after only a few minutes, is hot. Also, the aluminum plate/chassis is warm to the touch. Ventilation is per instructions.

At first, I was going to just let the tubes burn in to get rid of the hum. But when I noticed the heat, I became concerned. So, everything is unplugged.

Is this heat normal, and I just need to be patient with the tube burn in?

[CapnCook]

I think I may have figured out the popping.

When I attached and soldered the black wire from 12L to the lower lug of the headphone jack closest to the 9 pin socket, I did not manage to solder the the wire previously inserted from 3L. I suspect the force of inserting the headphone plug is causing that to move around, causing the popping?

I'll wait for a response before re-soldering.

What are the chances that is causing the hum?

[Tom-s]

1. The detached ground wire you describe should be soldered as per manual. Don't plug in headphones at this stage because it could damage your headphones.
2. Hum can be a tube problem, burn in could be the remedy. But in your case i'd say its because of the ground problem you describe. Solve this first, redo resistance; voltage checks and listen again.
3. The heat you describe sounds normal to me. Tubes get hot; like don't touch them- hot.

[CapnCook]

Thank you for reply. I'll go and re-solder that and retest and report back.

Regarding the heat, should plate get warm, too? It did seem more hot than just radiance from the tubes.

[Deke609]

Regarding the heat, should plate get warm, too? It did seem more hot than just radiance from the tubes.

Yeah, the chassis plate gets warm, and you're right, most of that heat isn't from the tubes. You've got two big white 10W rated resistors sitting against the chassis under the vent in the middle of the chassis plate. I don't how much power they are actually dissipating, but the fact that PB chose 20W combined suggests that those resistors are going to dissipate a fair amount of heat. Plus you've got two other 5W resistors near the transformer that are putting out some heat too.  (Think of how hot a 60W or even 40W light bulb gets - same principle here, just less heat). If you passed the resistance and voltage checks, you're all good.

cheers, Derek

[oguinn]

Yeah, the whole thing's going to get warm. That's why you need the rubber feet and the vent on the top of the chassis.

[CapnCook]

Yeah, the chassis plate gets warm, and you're right, most of that heat isn't from the tubes. You've got two big white 10W rated resistors sitting against the chassis under the vent in the middle of the chassis plate. I don't how much power they are actually dissipating, but the fact that PB chose 20W combined suggests that those resistors are going to dissipate a fair amount of heat. Plus you've got two other 5W resistors near the transformer that are putting out some heat too.  (Think of how hot a 60W or even 40W light bulb gets - same principle here, just less heat). If you passed the resistance and voltage checks, you're all good.

cheers, Derek

Excellent explanation. Thanks!

[CapnCook]

Yeah, the whole thing's going to get warm. That's why you need the rubber feet and the vent on the top of the chassis.

Makes sense. Thanks!

[CapnCook]

1. The detached ground wire you describe should be soldered as per manual. Don't plug in headphones at this stage because it could damage your headphones.
2. Hum can be a tube problem, burn in could be the remedy. But in your case i'd say its because of the ground problem you describe. Solve this first, redo resistance; voltage checks and listen again.
3. The heat you describe sounds normal to me. Tubes get hot; like don't touch them- hot.

Soldered it. Rechecked resistance and voltage, to b sure.

Headphones went in so quiet, I had to make sure it was on. Which also signified a pitch black background. Hum gone. Sounds sweeet!

Thanks for the guidance.

[oguinn]

Nice work. Post pics of your finished build

[CapnCook]

Took awhile to get back to posting pics. Listened to it anytime I got near it 

[Paul Birkeland]

Can I see some closeups of the wiring on the headphone jack?