Help with Trinity Plexi II Build

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Mt3418
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Joined: Wed 06/27/18 1:42 am

Help with Trinity Plexi II Build

Post by Mt3418 »

Hello all.

I have just finished putting together my first kit and have encountered a problem. While plugged into either channel on the hi input the amp sounds amazing. A little noise when the volume goes above 60% but nothing terrible. When I plug into the low inputs I get a lot of noise and almost no guitar sound. The noise is absent when the volume is off but comes in immediately when the volume is turned up and gets louder as the volume increases. While on the plexi channel the noise is a high pitched whine with static and on the normal channel its just static.

Anyone have any suggestions on where to look to resolve the problem?

Thanks in advance.
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Daviedawg
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Re: Help with Trinity Plexi II Build

Post by Daviedawg »

Hi There. My initial reaction is that if one of each pair of inputs is working properly but the other is not then the issue must be with the wiring of the Lo inputs at the socket or to the valve. There is very little that is not common to both inputs, I assume without seeing a schematic. I could not find a Trinity schematic with hi and lo inputs so maybe you could post the one you are working with.

Dd

Edit. Of course as soon as I posted above, I found the schematic. But it is as I expected. The difference in input is paralleling the two 68ks. So the only difference between hi and lo is how you wire the socket and from the input to valve. So two possibilities - the sockets are defective or the wiring is wrong. I think the former is not likely so you should review the way you have wired the two Lo input sockets and the 68k resistors. In fact look at all the socket and resistor wiring.
The way the two inputs work is that the Lo signal goes straight through the 68k it is connected to. The Hi uses the switched connection on the Lo jack socket to pass signal in a parallel action through both 68ks so reducing the input resistance and increasing signal strength. You will see that on the schematic but it is not necessarily obvious on a layout.
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geoff 1965
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Re: Help with Trinity Plexi II Build

Post by geoff 1965 »

hello,
this looks like a nice amp! have you used the standard layout or have you added the cascade switch? it helps if you can add some pics.
18WattPlexiMkIISchematic5.pdf
18WattPlexiMkIILayout6.pdf
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Mt3418
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Re: Help with Trinity Plexi II Build

Post by Mt3418 »

I fixed it. :D
I flipped the amp upside down to try to probe for the problem and it started working normally, so I knew it had to be a short somewhere. Followed the inputs but couldn't find anything. While scratching my head trying to find where the problem could be I absent mindedly flipped the fat switch and the noise instantly came back. I followed the fat switch wire back to the tube socket and found that the adjacent connection, at the second pin of the second preamp tube, had popped loose. Got it resoldered and now the amp sounds perfect. Even got rid of the mild noise when the volume is turned up.
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Daviedawg
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Location: Scotland

Re: Help with Trinity Plexi II Build

Post by Daviedawg »

Super outcome. Well done

Dd
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