2 channel amplifier based on Plexi and JCM800

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Antonio
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Location: Ribeirao Preto - Brazil

2 channel amplifier based on Plexi and JCM800

Post by Antonio » Thu May 18, 2023 6:08 pm

Hello! My name is Antonio and I live in Brazil.

I have a 2-channel handmade amplifier, one of them being Clean (based on Plexi) and the other, a Dirty channel (based on JCM800). On the JCM Channel, I have the option to use stock mode 2204 and mods #34 and #36 by Frank Levi.

Analyzing the construction, I had some doubts. I will be very happy if someone can help me with them.

1) I use 2 tubes 6550s in the power and I have a switch that allows to change the operation between triode mode and pentode mode. Do 6550s tubes go well in triode mode? Is there any risk in using triode mode? I ask this because I'm thinking of removing this switch that changes the modes.

2) The dirty and clean channels use halves of the first 12AX7, with half of the first triode for the dirty channel and the other half for the clean channel. As a way of connecting the 2 channels to the input, the builder connected the 2 grids of the triodes (check the photo). Is this a good solution? Is there any way to make this better? Is there a change in pitch or signal strength?

https://drive.google.com/file/d/1zSpgsI ... sp=sharing

These are some pictures of my amplifier's internal components. Do you have any suggestions for me? I want to get as close to a good Marshall sound as possible.
https://drive.google.com/file/d/1Hsou8I ... sp=sharing
https://drive.google.com/file/d/18WOXmv ... sp=sharing
https://drive.google.com/file/d/1e9U4Db ... sp=sharing

Thank you very much!

Kind regards,
Antonio.
Gibson Les Paul 1959 R9 "Jessica"
SIR #34/#36 Amp Replica

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CoffeeTones
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Re: 2 channel amplifier based on Plexi and JCM800

Post by CoffeeTones » Thu May 18, 2023 9:56 pm

Triode mode shouldn't break anything but is not a useful sound for me. If you like it, use it.

The input wiring, grid loads and switching arrangement will affect the extent to which the tone / signal is changed by having the input grids connected. Ideally, any preamp tube, input grid should be grounded or have a load resistor to ground when not in use. Without seeing the entire circuit or schematic, I will say it appears that both grids may be sharing the same jack and load resistor. If you want to know for sure if it is affecting the sound, simply cut the left grid resistor loose from the other and ground that floating / disconnected grid and give it a sound check.

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Antonio
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Just the numbers in order: 13492
Location: Ribeirao Preto - Brazil

Re: 2 channel amplifier based on Plexi and JCM800

Post by Antonio » Fri May 19, 2023 11:27 am

CoffeeTones wrote:
Thu May 18, 2023 9:56 pm
Triode mode shouldn't break anything but is not a useful sound for me. If you like it, use it.

The input wiring, grid loads and switching arrangement will affect the extent to which the tone / signal is changed by having the input grids connected. Ideally, any preamp tube, input grid should be grounded or have a load resistor to ground when not in use. Without seeing the entire circuit or schematic, I will say it appears that both grids may be sharing the same jack and load resistor. If you want to know for sure if it is affecting the sound, simply cut the left grid resistor loose from the other and ground that floating / disconnected grid and give it a sound check.
Perfect Coffee!

I will do this test.

https://drive.google.com/file/d/1hoHb91 ... p=drivesdk

Anyway, this is a photo of the board where the valve is connected, I believe they are sharing the same ground.
Gibson Les Paul 1959 R9 "Jessica"
SIR #34/#36 Amp Replica

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