Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mini612 on October 11, 2022, 08:32:08 pm
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I am currently building a 5E3, not from a kit but from sourced parts. I have decided to not do a replica but to do something a little different. I know that there are 4 channels; Normal 1 and 2, and Bright 1 and 2. So I have a 4P4T rotary switch laying around and decided to experiment with it to see if I can just use 1 input jack and select any of the channels with this rotary switch. I did the experiment on my 5f2a build and it worked, well on 2 channels of course, but I am sure the other channels will work as well if on the 5e3! But my concern is the unwanted hum, as it was humming a little louder than before.
When I did the experiment, I did not secure the 4p4t onto the 5f2 chassis, the 4p4t was outside of the chassis. I unsoldered the 5f2 inputs and used 1 of the inputs. I then used alligator clips to connect all the points. I connected the 1m resistor from the 4p4t to ground. Again, it works on each channel but it was giving a louder hum.
My questions: is there hum because of the way I wired it up, alligator clips and outside the amp? or will be this 4p4t give my amp more hum?
BTW, if I were to use this 4p4t, I will be using shielded wires and making sure all the ground wires be at a secure ground.
Thanks
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> is there hum because of the way I wired it up, alligator clips and outside the amp?
Seems likely. The input is the most sensitive point in the amplifier. It wants to suck-up all the hum/buzz field in the room. That is why we have closed metal boxes and shielded wire, right?
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> is there hum because of the way I wired it up, alligator clips and outside the amp?
Seems likely. The input is the most sensitive point in the amplifier. It wants to suck-up all the hum/buzz field in the room. That is why we have closed metal boxes and shielded wire, right?
Yes! I’m going to try to use this rotary switch on a 5e3 as it did work on a 5f2. I will be using shielded wires (4 of them) and if that don’t work, I will shield the whole rotary assembly with something. I will also be using a on/off/on 3 position switch for channel 1 and channel 2 combine. I think it’ll work but it’s the unwanted noise I'm concerned about. Thanks!!!
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Update: completed the 5e3 and the 4p4t switch works along with a on/off/on switch (used for combining channel 1 with 2). I used shielded cables for the 4 channels. Not much unwanted noise that I can hear at this time. BUT, it's having other issues. I might have to start a new thread for this. The issue is Channel 1 volume and MV pot is acting a bit weird. I used Trainwreck, PPIMV, with a 1m pot. When MV is at position 1 (starting to open), low volume overdrive/distortion and as I increase the MV past 1/4 to max, it cleans up, in other words, Its not acting like a MV.
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Show us an as-built schematic.
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Show us an as-built schematic.
Hi Sluckey,
I am new to tube amp building so I still have to figure out how to put this in a drawing. I am still trying to figure out the master volume as it's not working like how it should. I am unsure if the input system is the cause of this. It's wired exactly like how Rob Robinette described: Trainwreck Type-3 PPIMV.
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It's wired exactly like
did you take a chunk of schematic and use it out of context?
what you feed the pot and what the pot feeds are bigger factors than if i wired 3 wires right.
^what Sluckey said
without a schematic, all I see is the forest
fwiw, i did the aluminum tape, caused weird stuff, it's too abstract to be appreciated by many :icon_biggrin:
Spend some quality time looking at Sluckey's page, the layouts, I got better, anyone can :laugh:
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The Trainwreck Type-3 PPIMV is the least loved of all the MV types. I found it nearly useless. I really doubt Rob thought it works great!
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The Trainwreck Type-3 PPIMV is the least loved of all the MV types. I found it nearly useless. I really doubt Rob thought it works great!
You are absolutely right! I just changed it to pre phase inverter. It works well! The amp sounds good, to me. But I don't have a 5E3 to compare it to except youtube sound clips.
I still have a lot to learn but I'm enjoying it so far. Thanks everyone!
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… It's wired exactly like how Rob Robinette described: Trainwreck Type-3 PPIMV.
I can’t think how that’s possible?
The Trainwreck Pages shows master volume circuits for Marshalls, connected to an LTP phase splitter.
Whereas a 5E3 has a cathodyne phase splitter.
Things work as part of a system, they interact with, and are affected by, the circuits at their input, output and power supply.
Often it can seem that amps are just a bunch of circuit building blocks strung together, and if they’re lucky beginners can proceed on that basis, but eventually an incompatibility will emerge and things won’t work as expected.