Blown PT?

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JMPGuitars
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Re: Blown PT?

Post by JMPGuitars »

Post some updated photos. Check your voltages and post them too.
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Riffmonster
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Re: Blown PT?

Post by Riffmonster »

I was about to measure the voltages. Plates on V1 are about 130V and Plates of the El84 about 352V. Screens of the EL84 around 330V. When I try to measure the plate voltages of the phase inverter, a loud pop appears once I touch the pin with my probe. I can not really measure the voltages there.
:?
The pictures are from yesterday without the shielded wire and without the grid stopper.
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geoff 1965
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Re: Blown PT?

Post by geoff 1965 »

if you make a dummy load for the speaker jack you can test all the voltages safely without damaging your output transformer.
001.JPG
this one is 100watt 8ohm wirewound.
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Riffmonster
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Re: Blown PT?

Post by Riffmonster »

That’s true, I forgot about using a dummy load. I actually have one at home and will post the last voltages after work.
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Re: Blown PT?

Post by Riffmonster »

So I have 226V at the plates and 36V at the grids and 69 at the cathodes of the phase inverter. The 36V seems a bit low, given 20% tolerance. Cathodes of the El84 is 10V
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geoff 1965
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Re: Blown PT?

Post by geoff 1965 »

regarding grounding,my lite2 is a cage layout with the valves at the front so is a different layout to yours but here's the difference with the grounding; i have the input jack and tone pots grounded seperately from the B+, phase inverter ground. also my el84 bias is grounded seperately,you might want to try this and see if it helps.this is the layout i worked from with some ammendments to grounding.
18W_LITE2B_LAYOUT_BrownNote_TRANS_FINAL_v1.1.jpg
what value bias resistor for the el84's have you used?
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Riffmonster
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Re: Blown PT?

Post by Riffmonster »

Thanks for the input! I will probably try out the different ground and see if it helps.
I have a 150R resistor with a 47uf cap.
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Daviedawg
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Re: Blown PT?

Post by Daviedawg »

Your voltages seem a bit awry. On the power valves you should have a target of 12v on the cathodes and a difference a little less than that between pins 7 and 9 plate and screen. Can you post a full list of your voltages? Or you can refer to the standard examples posted in the downloads for a comparison, bearing in mind that they are for a traditional 18 watt. Then go from there.

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Riffmonster
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Re: Blown PT?

Post by Riffmonster »

Hey Dd,

sorry for the late reply. Here are my voltages:

V1:

Pin 1: 149
Pin 6:149

V2
Pin 1: 234
Pin 6: 230
Pin 3: 78
Pin 8 :78
Pin 2: 38
Pin 7: 37

EL 84s

Pin 7: 340
Pin 9: 323
Pin 3: 10

To me they seem not too weird, but I might be wrong.
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Daviedawg
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Re: Blown PT?

Post by Daviedawg »

Seeing them all together I agree that there is no reason to think that they are causing any issue.
Just as an aside. For best tone I would adjust your power valve cathode resistor to get the cathode readings up from 10v to as close to 12v as possible. It really is a noticeable difference. Try a 125 ohm.

Dd
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Riffmonster
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Re: Blown PT?

Post by Riffmonster »

Thanks, that could be worth a try.
However, I am a bit frustrated by now and will just let it be. I triple checked every connection and the voltages are okay too, I just can not find the reason for the noise.
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Daviedawg
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Re: Blown PT?

Post by Daviedawg »

Do not get despondent. We have all been there with build issues, especially grounding problems and sorted them eventually.

To recap, you are getting hiss when the guitar is not grounded by you touching a grounded part. How high is the volume when it becomes apparent? What guitar is it and is it the same with other guitars?

If we eliminate the instrument as an aggravating factor then we can look for the cause in the amp from the start again.

Dd
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Riffmonster
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Re: Blown PT?

Post by Riffmonster »

Thanks for encouraging Dd!

I tried different guitars, so it is not the guitar. The noise is immediately there when I just turn up the volume a little. I am not sure if it came from resoldering so much but now I also have a hum besides this noise. The hum is not affected by the volume or tone pot though. The noise is affected by the volume a lot and by the tone a lot too (more treble = more noise).

Cheers
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geoff 1965
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Re: Blown PT?

Post by geoff 1965 »

hello,
have you tried the different grounding and the 10-15K grid stopper?
the lite2b tonestack is the tonestack from the classic 18W tremolo channel and is more interactive than the normal channel i.e. the wiper of the normal channel tone pot goes to ground whereas the wiper from the lite2b tone pot feeds into the wiper of the volume pot.you will notice adjusting the tone will also adjust the volume and from what you describe the hiss must be in that area.i would try a grid stopper and rework the grounding,i know it can be frustrating but stick at it i'm sure you will sort it.
good luck
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Re: Blown PT?

Post by JMPGuitars »

JMPGuitars wrote:
Wed 06/12/19 2:52 pm
Ground schemes: viewtopic.php?f=4&t=25372
What this guy said. ;) The layout referenced in that post is a Lite 2b. That's the ground scheme you should be using.

Maybe it would be a good idea to post a sample of the noise so we can hear what you hear.

Thanks,
Josh
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Re: Blown PT?

Post by Riffmonster »

Hey guys,

i am using the partial star grounding like in your layout. Here is a video. Volume is like only at 1. Hope that gives some kind of impression. I switch from touching the guitar and not to show the difference and then i play with the tone pot.
https://youtu.be/Vl-nZJctXcM
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Re: Blown PT?

Post by JMPGuitars »

That doesn't sound like hum to me, it sounds like buzz. Check your filter caps first. You can try tapping them with a chopstick and see if anything is suspect.
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Re: Blown PT?

Post by Riffmonster »

Yeah there is only a slight hum in the background, the audible noise is hiss/ buzz.

Thanks for the tip, I’ll chopstick them after work. But what could have made them bad? They were new and I didn’t put them in the wrong way.
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Re: Blown PT?

Post by crgfrench »

Riffmonster wrote:
Sun 06/23/19 1:31 pm
Yeah there is only a slight hum in the background, the audible noise is hiss/ buzz.

Thanks for the tip, I’ll chopstick them after work. But what could have made them bad? They were new and I didn’t put them in the wrong way.
Did you form them with a variac at first powerup?
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Re: Blown PT?

Post by Riffmonster »

crgfrench wrote: [quote=Riffmonster post_id=243169 time=<a href="tel:1561314677">1561314677</a> user_id=38134]
Yeah there is only a slight hum in the background, the audible noise is hiss/ buzz.

Thanks for the tip, I’ll chopstick them after work. But what could have made them bad? They were new and I didn’t put them in the wrong way.
Did you form them with a variac at first powerup?
[/quote]

Nope, I don’t have a variac at hand right now.
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