problem with this clone

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cisatracurio
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problem with this clone

Post by cisatracurio »

hello good to all and congratulations for the forum.
I have this clone of plexi I think of 18 watt made up of two 12ax7 and two el84
with its four send-return inputs
the problem is that when the channels are bridged and I use the bass pickup on the 6 and 5 strings the sound drowns out.
I have changed valves and it remains the same.
if I use the return it sounds good.
where can the fault be?
I had thought to fix it or even make a new board taking advantage of the rest of the components.
I attach photos.

Thanks .
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Bieworm
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Re: problem with this clone

Post by Bieworm »

cisatracurio wrote:
Tue 04/20/21 10:39 am
hello good to all and congratulations for the forum.
I have this clone of plexi I think of 18 watt made up of two 12ax7 and two el84
with its four send-return inputs
the problem is that when the channels are bridged and I use the bass pickup on the 6 and 5 strings the sound drowns out.
I have changed valves and it remains the same.
if I use the return it sounds good.
where can the fault be?
I had thought to fix it or even make a new board taking advantage of the rest of the components.
I attach photos.

Thanks .
Hey.. I think you need to give us more information. If it's a 4 input 18W there is likely no bridging the channels. It will be out of phase and that's the thin sound you hear.
Also.. don't re-use components from a turretboard. That's screaming for problems. If I were to rebuild an amp I'd only reuse the existing transformers .. heck I even throw away the tube sockets. In my understanding a rebuild is a situation where you can't find the problem in the amp and start over... so it's not smart to use components again. You gave a big chance of reintroducing the same problem in the new build. But likely there is nothing wrong with your amp..so why rebuild it?
Post pictures so we can see what we're dealing with.
Thanks .. and welcome 🙂
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cisatracurio
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Re: problem with this clone

Post by cisatracurio »

Hello, thanks for the answer
attached several photos of the team
the truth is not a great idea to rebuild it just solve the problem

Thank you
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cisatracurio
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Re: problema con este clon

Post by cisatracurio »

D125932D-574D-4C6C-A481-02DAD7C7B96E.jpeg
0462E822-2196-46D4-97DB-354D51392A6E.jpeg
A419C4E6-2320-4308-82FB-D0D3D9D31392.jpeg
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I don't know if they will be well uploaded
You do not have the required permissions to view the files attached to this post.
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Bieworm
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Re: problem with this clone

Post by Bieworm »

Do you have a schematic of THAT amp? Not a standard plexi schematic, but the one from the amp you have. With the pcb board it's nearly impossible to see how it's wired. It's not traceable if it's wired to be jumpered. I don't think it's any high suality amp, but it should be fun to play anyway.
Can you post a sound clip of it with and without jumpering. The without jumpering channels should be one of each channel separately.
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cisatracurio
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Re: problem with this clone

Post by cisatracurio »

That seems to me from the little I know about it
I do not have the scheme and I can imagine that looking at the plate it is difficult to get an idea
tomorrow I will record the audios and upload them

Thank you
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geoff 1965
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Re: problem with this clone

Post by geoff 1965 »

is the potentiometer at the right side of the input jacks for blending the inputs rather than a jumper cable?
look at those screw terminals on the boards,tweakers delight!
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cisatracurio
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Re: problem with this clone

Post by cisatracurio »

that potentiometer on the right side of the inputs is a basic master volume.
I will look at the cables that come out of the inputs and go to the plate in case there is a bad connection because at first glance you cannot see any capacitor in bad condition
as soon as I have the sound samples I will attach them
the amplifier has a decent sound and a lot of volume so my intention to solve the problem

Thank you
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cisatracurio
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Re: problem with this clone

Post by cisatracurio »

Hi ,Another thing I can think of if I couldn't fix it.
With the transformers that I have, could I mount a plexi?

Thanks
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Re: problem with this clone

Post by Bieworm »

cisatracurio wrote:
Wed 04/21/21 3:22 am
Hi ,Another thing I can think of if I couldn't fix it.
With the transformers that I have, could I mount a plexi?

Thanks
Normally yes. It's the same kind of amp right now so..
But you need to check the specs of the transformers to be sure.
Anyway... this is no plexi. It's 1 tube short and the output stage of a plexi is way more powerful with EL34s.
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cisatracurio
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Re: problem with this clone

Post by cisatracurio »

Ok I understand that it depends on the specifications of the transformers.
What if I wanted it to be with the 84 so that it had 18 watts or can it also be with the 34?
And what scheme should I follow with diodes in the rectifier?

Thanks
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Re: problem with this clone

Post by Bieworm »

cisatracurio wrote:
Wed 04/21/21 5:15 am
Ok I understand that it depends on the specifications of the transformers.
What if I wanted it to be with the 84 so that it had 18 watts or can it also be with the 34?
And what scheme should I follow with diodes in the rectifier?

Thanks
Stay with the EL84. An EL34 will draw 2x the current and might not work with those transformers. And the OT will likely be 15 or 18W output...so there would be nothing to gain with EL34s
6V6 would be fine too.
Assuming your build runs with 2x 12ax7 and 2x EL84 the heater current is at least around 2.2 A. So with 2x 6V6 and 3x 12ax7 you should still be fine and make it a more similar preamp to plexi specs. There are several 6v6plexi schematics online and here in the download section available. Do you have experience in building tube amps?
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cisatracurio
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Re: problem with this clone

Post by cisatracurio »

Thanks Bieworm I understand that you tell me that due to the characteristics of my amplifier the transformer should ensure the power supply for the 3 12ax7 and 2 6v6 and thus make a more reliable scheme to a plexi.
I have very little experience in tube amplifiers if I have done other types of electronic assemblies and I understand a little about the operation of the valves
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cisatracurio
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Re: problem with this clone

Post by cisatracurio »

I think my amp can correspond in schematic to a superlite tmb from what I have been able to see?

Thank you
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Re: problem with this clone

Post by Bieworm »

cisatracurio wrote:
Wed 04/21/21 7:03 am
I think my amp can correspond in schematic to a superlite tmb from what I have been able to see?

Thank you
That is possible, but without a schematic or reverse engineering it's impossible to say that. There arelots of combinations with that same tube layout..
It would be wrong to advice you to start rebuilding it without proper soldering experience. Tube amps are dangerous to work on. If you're really erger to do it you should study amp works in advance
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