Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

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Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

Hello,

I finished this build a little while ago, and now looking to diagnose this noise issue. As mentioned it is like static or the frying egg sound. It occurs with nothing plugged into the amp. It is affected by the volume on the TMB channel, and not on the other channel. It does not vary noticeably from the EQ adjustment. It goes away when V2 is pulled but is there when only v1 is pulled. Everything is silent when both V1 and V2 are pulled. Tried swapping different tubes with the same results. Because of this I assume it is a component between V1 and the volume pot?

One other thing I noted that may or may not be related is that with both tubes pulled and rotating the volume pot it is perfectly quiet from 0 to 6 and then it starts to hum from 6-10.

Schematic is here: https://www.trinityamps.com/docs/18Watt ... matic5.pdf
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by Bieworm »

Did you check all soldering with a chop stick? Seems your problem is between the input and the volume pot on the plexi channel. Most likely a bad connection , but could also be a bad or over heated component. Those Mica caps (the 250p in your case) are notorious for failure with over heating.
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

It looks like that is the next step. I'll have to take it apart and get it back on the bench.
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by colossal »

Check the V2 plate resistor. Sizzling or frying noises, especially with carbon comp resistors, can be indicative of a failed part.
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

OK, I'm in. I should add that it intermittently has a high frequency hiss/squeal like tuning in a radio station. I haven't been able to find anything with the chopstick that makes the noise go on and off.
colossal wrote:
Wed 07/20/22 7:17 am
Check the V2 plate resistor. Sizzling or frying noises, especially with carbon comp resistors, can be indicative of a failed part.
There is an audible thump when I touch/move the wires connected to V2 pins 2 and 8, but it doesn't really seem to affect the static. The V2 plate resistor measures 100K. I found the V2 plate voltage to be 260 and voltage at V2 pin 1 and pin 8 to be ~150 rather than 180 as the schematic shows. V1 voltages are right on.
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by Unit_1 »

Kinda sounds like maybe you have a hairline fracture in one of those carbon comp resistors. This is why I use carbon film, same sound, more reliability especially as they age.

Chopsticking not working, can't find anything. Sounds like it's time for the shotgun method. Just start replacing everything in that signal path, one at a time (or else risk introducing another problem) and test after each change.
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by JMPGuitars »

perplexd wrote:
Fri 07/22/22 12:00 pm
OK, I'm in. I should add that it intermittently has a high frequency hiss/squeal like tuning in a radio station. I haven't been able to find anything with the chopstick that makes the noise go on and off.
colossal wrote:
Wed 07/20/22 7:17 am
Check the V2 plate resistor. Sizzling or frying noises, especially with carbon comp resistors, can be indicative of a failed part.
There is an audible thump when I touch/move the wires connected to V2 pins 2 and 8, but it doesn't really seem to affect the static. The V2 plate resistor measures 100K. I found the V2 plate voltage to be 260 and voltage at V2 pin 1 and pin 8 to be ~150 rather than 180 as the schematic shows. V1 voltages are right on.
You might want to change your plate resistors to metal film. Definitely make sure your 1M resistors at the input jacks are metal film (R1 and R26).

Post some detailed/high quality photos of your build.

Thanks,
Josh
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

JMPGuitars wrote:
Sat 07/23/22 3:32 pm
Those image links don't work. I dunno if you can see the images, but nobody else is authorized to, so there's just a minus symbol there.
Test.

Image
Last edited by perplexd on Sun 07/24/22 10:03 am, edited 3 times in total.
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by JMPGuitars »

Those image links don't work. I dunno if you can see the images, but nobody else is authorized to, so there's just a minus symbol there.
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by High Plains Drifter »

hey
I'm new here
I gonna suggest a couple things
1. clean that board
2. swap in another 250pF Treble cap....just tack a new one in...any ceramic or film or whatever just to eliminate that mica cap in tone stack.
Those brown mica notorious for being destroyed during soldering (as mentioned).
You might try Vishay/Ceramite 562R type and see if you like it....great pF caps.
If you stick w/Mica...heatsink the leads when you solder it in.
This is where I would start...
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by JMPGuitars »

Please also post a video so we can hear the issue.

Reviewing the photos, a few things stand out. You should review the soldering technique thread/videos in my signature. Static can also be caused by a bad solder joint.

Thanks,
Josh
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

Video requested: https://imgur.com/pywWvcP

Jason
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by Bieworm »

perplexd wrote:
Sun 07/24/22 8:02 pm
Video requested: https://imgur.com/pywWvcP

Jason
Jason.. IMHO that's a classic cold or flimsy solder joint tone🤘😀
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by JMPGuitars »

solder-joints.jpg
In green are the 3 best joints I can see in the image. The red circles are the worst I see, and the red rectangle is pointing out that whole section could be better.

Review my soldering technique thread and videos in my signature. I see both hot, cold, and other variations of soldering issues in those solder joints.

Make sure your soldering iron is touching both the turret, and the lead in the turret. Those fat leads on the carbon comp resistors will act as a heatsink if they're not properly heated. You can see they didn't properly bond.

Thanks,
Josh
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

Thanks to all for your feedback! I will start by reworking the solder joints and go from there.
@JMPGuitars Thank you for the soldering references. I chose to put the components in the turret holes because that was how my Hiwatts were constructed, however I don't think that I would do it this way again. I quickly realized the challenges of soldering on both the top and outside of the turret without reflowing one or the other.

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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by JMPGuitars »

perplexd wrote:
Mon 07/25/22 2:48 pm
@JMPGuitars Thank you for the soldering references. I chose to put the components in the turret holes because that was how my Hiwatts were constructed, however I don't think that I would do it this way again. I quickly realized the challenges of soldering on both the top and outside of the turret without reflowing one or the other.

Jason
While I obviously prefer the outside of the turret, the tops of the turrets can be used for perfectly fine solder joints. It simply takes practicing the right way, with the right heat, in the right place. The soldering videos give great examples of what solder joints should look like, how to apply heat and solder, etc.

Don't feel bad about the state of your soldering. Everybody starts somewhere, and all of us can improve. I still go back occasionally and rewatch those soldering videos too. There's a plethora of members on here that can show you their old (and scary) soldering, and the world of difference compared to what they produce now.

Thanks,
Josh
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

I was able to get into it tonight and retouched some of the joints around V2 and tone stack and voila, it's fixed! I plan to go through and make sure everything is looking good and retest before I button it back up. Thank you!
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by perplexd »

OK, another question about the volume control on Channel 2. It is fine up to ~noon with a quiet shhh sound, then just past halfway, at a very specific point, a hum is introduced and then at 3 O'clock the hum drops off. You can also hear scratchiness in the wiper through this section especially when moved quickly. The shhh gets louder from this 3 O'clock position up to max. Ideas?
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Re: Diagnose Static/Egg Frying in Trinity 18 Watt Plexi MkII

Post by JMPGuitars »

Scratchiness on pots often means you have DC voltage leaking to the pots. The sectional behavior could also be related to a parasitic oscillation. Check for DC voltage on your pots, check that the capacitors aren't leaking, and if that all passes, you can try chopsticking to isolate/solve the issue.
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