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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Sat Oct 15, 2016 9:53 pm 
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What were your voltage readings for v4 and v5 after the swap ?

I Don't think you will get any sound from the normal channel as you don't have any plate voltage on the triode V1 pin 6 should be the about the same as v1 pin 1

Try a different tube in v1 see if it makes a difference


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Mon Oct 17, 2016 2:29 pm 
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Ok, these are my new voltages fro V4 and V5,
V4
1. NC
2. 43 mVDC
3. 13.3 VDC
4. 3.3 VAC
5. 3.3 VAC
6. NC
7. 359.5 VDC
8. NC
9. 347 VDC

V5
1. NC
2. .9 VDC noisy
3. 12.62 VDC
4. 12.62 VDC
4. 3.3 VAC
5. 3.3 VAC
6. NC
7. 362 VAC
8. NC
9. 347.9 VDC

I noticed that the pin 2 on my V5 tube seemed to change values as I adjusted the volume on my normal channel. I wasn't able to thoroughly test this as whenever I turn up the volume on my normal channels I get a crazy amount of static the I feel may damage my speaker, amp, or ears.
I did switch around some of my pre-amp tubes and was able to get a sound out of my normal channel. However this was completely overshadowed by the insane level of static coming out of the amp even when the volume was on one.


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Tue Oct 18, 2016 10:01 pm 
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Do you have any dc voltage on the pot side of the .0047 cap for v1 normal channel


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Sun Oct 23, 2016 3:50 pm 
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On the pot side of the .0047 cap I have 0 VDC on the tube side of the cap I have 144 VDC


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Wed Oct 26, 2016 2:41 pm 
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Check your wiring around the two pots for the normal channel make sure the components leads are touching any of the pot shells. From the picture it looks like one of 500pf cap is touching the middle leg of the volume pot.


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Mon Oct 31, 2016 3:44 pm 
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I double checked my wiring and it does seem like the 500pf cap was touching the chassis. I have fixed this. Now all channels run and sound great, but there is a hum with the amp and a winds sound. The hum seems fairly normal and isn't that invasive. The wind sounds is more present. It is easier to ear at lower volumes, and it sounds like there is some wind running through the amp. Any help on what could be causing such a sound?


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Tue Nov 01, 2016 10:18 am 
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could be tubes

could be weak or bad ground in one section

could be wiring you can run the amp and check with no conductive probes moving wires around i.e. chop-sticking. when you move wires around listen for noise disapearing and new noises


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Tue Nov 01, 2016 10:24 am 
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In my experience, it can be the carbon comp resistors or a noisy tube. Try swapping around tubes.

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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Wed Nov 09, 2016 11:44 pm 
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So I switch around my tubes and I've mitigated the wind sound. However I now notice that as I turn up the volume of my normal channel the amp will start to crackle. This can get very loud. Any suggestions on what could be causing this?

Cooper Cordero


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Sun Nov 13, 2016 6:45 pm 
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So, I just ran some voltage measurements through the amp and it was looking better. I started to play through the amp and it sounded great, but then it seamed to fall out of place. The amp started crackling, popping, and hissing very loudly. I wasn't able to take any voltage reading after this happened because the amp was so loud whenever I turned it on. Any idea what could have happened to the amp for this to happen?


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Wed Nov 16, 2016 11:15 am 
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Bad solder joints are the first suspect. Redo them and triple check that the input cables are installed correctly.

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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Wed Nov 23, 2016 3:24 pm 
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Alright,
So I checked the solder joints and fixed up any that looked not perfect. I did a sound check after this and nothing had changed. But later that day I turned the amp back on and it crackled for a little bit, then it just stopped. I ran a sound check on the amp afterwards and there was very little ambient sound, but the amp has seemed to gone backwards in the processes of fixing things. I no longer have full range of sound through the amp, and whenever I play I notice a very present crackling on the sound coming out of the amp. In addition, my output tubes have gone out of bias, and v5 is red platting again.
Any clue why this would have happened, or how to fix it?

Cooper Cordero


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Mon Dec 12, 2016 4:00 pm 
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Hello again,
I am heading home for the holidays very soon and was planning on spending some time trying to get my amp up and running. What should I do to try and fix my amp. I still am experiencing a very detrimental crackling when I try and play. My tubes are also very far out of bais, again. Any clue what I might have done to almost go backwards with my progress?
Any help is very much so appreciated.

Cooper Cordero


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Sat Dec 17, 2016 9:36 am 
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Check, redo the solder joints everywhere the OT connects into the circuit.

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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Fri Jan 06, 2017 4:28 pm 
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Hey guys,
So I redid the solder joints, and found a bad joint. I fixed it and this resulted in a big change in the amp. Now the amp has full range of sound through it. However, now there is a very loud wispy sound. The wispy sound is unaffected by the volume knobs. The wispy sound does get affected by the tone knobs. Do you guys know what might be causing this sound?
Thanks for all the help so far

Cooper Cordero


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Sat Jan 07, 2017 9:31 am 
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By wispy do you mean hiss? Steady level? This could be affected by the treble more than the other controls. And how loud is it. Tube amps are not silent like solid state ones.

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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Tue Jan 10, 2017 11:19 am 
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The wispy would was more alike to the sound of wind going through the amp than anything else. It almost sounded like there was a very noisy phaser in my amp. The sound would oscillate very rhythmic. However, When I turned on my amp to check on the wispy sound, is was gone. Now I have no background noise, but my guitar crackles when I try to play. I did not change anything from when the wispy sound was present, to when the guitar sounded crackly.
Do you know what might have caused this change without me actively doing something?


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Tue Jan 10, 2017 8:42 pm 
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Environment. Noisy mains? Fluorescent lights? Lack of shielding of chassis.? Static in the dry air?

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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Wed Jan 11, 2017 8:59 pm 
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So I know that I can check the mains for noise and I can turn off any florescent lights, but how should I test the shielding and static in the air? Can these small differences really change the amp that drastically?
Also I forgot to mention in my most resent post that when the crackling returned my V5 tube began to overheat again.


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 Post subject: Re: 18 Watt Plexi Mk II
PostPosted: Sat Jan 14, 2017 12:30 am 
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Cmcordero wrote:
Also I forgot to mention in my most resent post that when the crackling returned my V5 tube began to overheat again.


I think you better redo your solder joints all around V5.

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