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 Post subject: Which 18 watt do I have?
PostPosted: Sat Feb 16, 2019 1:26 pm 
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I recently purchased this. Can you tell which 18 watt circuit it is, and what alternative parts were used? I know the seller said it has Zoso caps, which you can see. There may be other alternative parts, though.


Last edited by Zenpeace69 on Tue Feb 19, 2019 2:51 pm, edited 1 time in total.

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PostPosted: Sat Feb 16, 2019 4:03 pm 
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That's an older Plexi Model. Schematic is here:

http://www.trinityamps.com/docs/18WattP ... matic9.pdf

Attachment:

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PostPosted: Sat Feb 16, 2019 4:39 pm 
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coco wrote:
That's an older Plexi Model. Schematic is here:

http://www.trinityamps.com/docs/18WattP ... matic9.pdf

Attachment:
Plexi_layout_Docs_17Apr11 (2018_11_12 22_26_41 UTC).pdf


Thanks, do you recognize which other parts are alternative to the originals other than the Sozo caps?


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PostPosted: Sat Feb 16, 2019 4:45 pm 
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You will need to review the layout I posted and compare them. The rectifier diodes for sure and something around the PI tail resistor.
Poor job of installing them too because they are floating inside the chassis. I would make them permanent if you are able and you like the mods.

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PostPosted: Sat Feb 16, 2019 5:30 pm 
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coco wrote:
You will need to review the layout I posted and compare them. The rectifier diodes for sure and something around the PI tail resistor.
Poor job of installing them too because they are floating inside the chassis. I would make them permanent if you are able and you like the mods.


Unfortunately, I can't read the schematic.


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PostPosted: Sat Feb 16, 2019 7:18 pm 
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coco wrote:
That's an older Plexi Model. Schematic is here:

http://www.trinityamps.com/docs/18WattP ... matic9.pdf

Attachment:
Plexi_layout_Docs_17Apr11 (2018_11_12 22_26_41 UTC).pdf


So you think this one has been modded from stock for sure? It doesn't seem to have much gain.


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PostPosted: Sat Feb 16, 2019 7:45 pm 
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The Green wire that goes from the impedance selector to the PI tail is some sort of an attempt at negative feed back that would not work correctly.

The diodes in the rectifier I have seen something like that on the Ceri@tone layouts as a protection diode

But with the red wire coming off the rectifier tube going no where. dont think its using the tube rectifier

As for all the other diodes no clue to what someone was thinking

As Coco says see if you can get it back to stock


.


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PostPosted: Sat Feb 16, 2019 10:29 pm 
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sazafraz wrote:
The Green wire that goes from the impedance selector to the PI tail is some sort of an attempt at negative feed back that would not work correctly.

The diodes in the rectifier I have seen something like that on the Ceri@tone layouts as a protection diode

But with the red wire coming off the rectifier tube going no where. dont think its using the tube rectifier

As for all the other diodes no clue to what someone was thinking

As Coco says see if you can get it back to stock


.


Thanks for chiming in, you are correct about the tube rectifier. It's not currently wired in, it's got a solid state rectifier.

I know how to drain caps, and have biased amps before, but have never tackled a schematic.

Is this circuit way off, or just off a little? I could probably manage getting it back to stock if it wasn't too wonky in there. I will have to do some research on schematic symbols, though.


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PostPosted: Sun Feb 17, 2019 12:59 pm 
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You don’t really need to know how to read a schematic
The layout is easier it’s more of a paint by numbers thing

As for being off the ordinal not that far off

By the looks of it just the power supply rectifier and now that I looked at it again think all those extra diodes are zenners for voltage reduction

And the othe part that’s off is the phase inverter potion of the board where the tried to add negative feed back

What part of the world are you in?


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PostPosted: Sun Feb 17, 2019 4:54 pm 
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zeners make sense because he went to a solid state rectifier.

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PostPosted: Tue Feb 19, 2019 2:35 pm 
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Ok, a fresh set of JJ EL84's just arrived in the post today. I had a sinking suspicion this thing had more gain, it appears the power tubes that came with it were worn out. This amp actually has a ton of gain, and it appears those diodes were put in to make it solid state rectified.

I see no need to change this amp now. It's quite nice now.

Thanks, everyone!


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PostPosted: Tue Feb 19, 2019 4:37 pm 
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Fair enough but you should make them more robust. Specially those flying diodes.

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PostPosted: Sat Feb 23, 2019 1:48 pm 
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coco wrote:
Fair enough but you should make them more robust. Specially those flying diodes.


Yeah, I think you're right. I have it on a tech's bench right now. He is going to undo the flying diodes and the solid state rectifier and hook back up the tube rectifier. He thinks the mod was done to change the tone of the gain.

What's a good new production tube that sound alright in the tube rectifier?


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PostPosted: Sat Feb 23, 2019 6:23 pm 
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Zenpeace69 wrote:
What's a good new production tube that sound alright in the tube rectifier?

JJ EZ81 are fine.

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