Help! Matchless Spitfire Inspired clone

[luistrindade83]

Hello,

I’ve built an Spitfire inspired clone with some parts that I had laying around, components that I wanted to give some use, and with what I had at my disposal I chose the Matchless.

The only problem, I’ve used the Ken Watts and Ceriatone layout, the only problem with the amp is the hum, too much for my taste, I’ve been poking around and trying to find out the problem for this, but it is really annoying me. Can you guys give it a look and maybe suggest some strategies to correct this.

[Phil_S]

Things that will help get an answer:
1) Better pictures. One showing an complete overview and maybe a few close ups, one of the topside of the chassis, and . We need to be able to click on them so they will enlarge. I can't get what you posted to enlarge. (Maybe that's just me.)
2) If you have an idea of whether it is 60Hz or 120Hz (assuming North America, otherwise 50/100.) Guitar low E is 82Hz. Guitar A string is 110Hz, so you have a reference to judge.
3) Does anything you do change the hum, and if so, how?
4) Post a schematic and a layout diagram if you have these. If you deviated, see if you can give us a marked up copy.

[luistrindade83]

I’ll try to post some images with better quality. It’s a 60hz hum, I’m sure of that, the strange thing is that it reacts with the pots, especially the master and tone, it grows with them being dialed to full position.

Another thing that I can say is that some resistor and two capacitors are to sensitive to the touch, the ones in the preamp section. Other than that is all normal.

EA488073-FDA4-4987-817A-A3ACC61366B3.jpeg

EA488073-FDA4-4987-817A-A3ACC61366B3.jpeg

C5520774-D93C-49F3-8238-6337F7E31574.jpeg

Thank you!
I’ll try to had the layouts later.

[T Wilcox]

does your 6.3v have a center tap?

[luistrindade83]

I made one with two 100ohm resistors to ground.

1011850D-9886-4BA2-A831-503BC8531F09.jpeg

[T Wilcox]

Well thats probably not the problem then.
Check continuity for all your grounds as well as making sure none were missed and possibly chopstick the wiring around v1 and see if you make the hum change at all if you havent already

[T Wilcox]

i dont see the ground coming off terminal 1 of your bass pot

[luistrindade83]

Touching the v1 gives me crackles and noise, but it doesn’t affect the noise, the wiring was all done twice, but without any improvement.

I wired the pot as is in the layout.

I followed the following two layouts:

CF8DDB9B-7869-4C1C-AB2C-4EFF06D18C49.jpeg

1DBE0FAB-B678-4225-8121-07FA9257910C.jpeg

[T Wilcox]

My bad, I was looking at a lightning layout
Other than those suggestions thats all I got at the moment

[T Wilcox]

Its hard to tell but zooming in your first filter cap (F&T) looks like it says 330 but its smudged so Im unsure but that should be either 30 or 33uF depending on which layout you stuck with.

[luistrindade83]

Its hard to tell but zooming in your first filter cap (F&T) looks like it says 330 but its smudged so Im unsure but that should be either 30 or 33uF depending on which layout you stuck with.

It’s a 33uf capacitor, I used two 33uf and two 22uf.
The decoupling capacitors are .001 and .002, didn’t use the ceramic one on the pots.

[Phil_S]

... It’s a 60hz hum, I’m sure of that, the strange thing is that it reacts with the pots, especially the master and tone, it grows with them being dialed to full position.

This is an amateur's diagnosis. Others here have pro status, so take what I say with a grain of salt. There is some bleed over of the 60Hz running on the 6.3VAC filament circuit. When you open up those pots, the 60Hz signal is being amplified.

There is nothing wrong with your style of wiring the filament string. That is my personal preference and it is easy to get a good result. You might chopstick the filament string and maybe you can move it just enough to get it out of range. Otherwise, I suggest rewiring, which I know is a PITA. You can rewire one section at a time and stop when the problem is cured. If you are rewiring, use the other style of running a filament harness, where you tuck it into the fold of the chassis. In that style of wiring, the filament supply will hug the chassis floor, running under the signal wires. You can then lift the signal wires so they are away from the filament wires. So, there is a clear chance doing any or all of this will not give you the result you want.

Good luck.

[luistrindade83]

... It’s a 60hz hum, I’m sure of that, the strange thing is that it reacts with the pots, especially the master and tone, it grows with them being dialed to full position.

This is an amateur's diagnosis. Others here have pro status, so take what I say with a grain of salt. There is some bleed over of the 60Hz running on the 6.3VAC filament circuit. When you open up those pots, the 60Hz signal is being amplified.

There is nothing wrong with your style of wiring the filament string. That is my personal preference and it is easy to get a good result. You might chopstick the filament string and maybe you can move it just enough to get it out of range. Otherwise, I suggest rewiring, which I know is a PITA. You can rewire one section at a time and stop when the problem is cured. If you are rewiring, use the other style of running a filament harness, where you tuck it into the fold of the chassis. In that style of wiring, the filament supply will hug the chassis floor, running under the signal wires. You can then lift the signal wires so they are away from the filament wires. So, there is a clear chance doing any or all of this will not give you the result you want.

Good luck.

Thank you very much for your insight, you’re for sure more experienced than me. I’ve reworded the filements twice now, the one with best results was this one, the last. Moving the heaters with a chopstick doesn’t change the hum, but when I move the wires on the v1, the chopstick acts like an antena, causing more noise and crackling. Sorry if sometimes I’m not able to fully express, in detail, the symptoms of the amp, and some technical stuff, just a lover, and portuguese!

Thank you all.

[Phil_S]

I have no Portuguese. You have very good English!

I think you may have 2 or 3 problems at V1. I suggest rewiring V1. Look at the Ceriatone layout. Jumpers are used to connect pins 1+6, 2+7, and 3+8. Use heatshrink or other insulation as needed on the jumpers to be make sure they don't touch and short. Keep all the signal wires between the board and the socket. There should be nothing between the socket and the back wall of the chassis.

This will do a few things:
1) Eliminate the wire loops around the socket. Less wire is less opportunity to pick up noise.
2) Make new solder joints. I think you may have at least one bad solder.
3) Separate the filament supply from the signal wires.

[M Fowler]

It's really hard to say what the hum problem is.

The Spitfire is one of my favorite amps and gigged with one for many years.

Walk away from it and come back to it later. Always seems to help me.

Mark