Help! Matchless Spitfire Inspired clone

[luistrindade83]

First of all, let me thank you all for the help.

I´m now, after rewiring the V1, getting a new symptoms, with the controls maxed, and the guitar volume as well, I´m getting feedback, without playing.

Can figure out what is happening, can the pots be the problem? I used mini pots, not those 24 mm that I normally use, but the values and voltage ratings are the correct ones.

[Phil_S]

I don't know what is making the squealing noise. I suggest it is all related to the first gain stage, somewhere between the input jack and the cathodes of V1.

The input jack lead dress (how the wires are run) is done poorly. The wires are much too long. I would remove both red wires and the white wire and replace them with the shortest possible amount of wire. Any wires that cross should cross at 90 degrees. I don't know if this will help, make it worse, or do nothing. If this was my amp, I'd do it.

[luistrindade83]

I don't know what is making the squealing noise. I suggest it is all related to the first gain stage, somewhere between the input jack and the cathodes of V1.

The input jack lead dress (how the wires are run) is done poorly. The wires are much too long. I would remove both red wires and the white wire and replace them with the shortest possible amount of wire. Any wires that cross should cross at 90 degrees. I don't know if this will help, make it worse, or do nothing. If this was my amp, I'd do it.

Thank you for the help, did it all I could, don’t understand what’s going on. Very strange behavior, it looks like it’s going on some kind of interaction between the controls, there a spot where no hum or noise is induced, after certain point it appears on the signal.

[luistrindade83]

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[Phil_S]

I don't know what the problem is. I was hoping someone more experienced might jump in, but it didn't happen. It may help to try some diagnostic work.
Power up the amp with only the power section tubes. No noise? Suggests the problem is somewhere else. Noise is present? The problem is in the power tube section.
Add V2 and power up. No noise? Problem isn't here. Add V1. Have noise? The problem is caused by the section supporting V2. Look in this section of the amp for a problem.
No noise with V2? Add V1. Noise is present? Now we know the problem is around V1.
Try to isolate the problem. This may take time.
Because you can set the controls to eliminate the noise, I am thinking you have a lead dress problem or two components are too close or touching. Just looking at the pictures, I think the problem is lead dress (wire placement.)
Tell us what you find by pulling tubes.

[luistrindade83]

I´m really glad for your help.

I´ve been messing around, soldering over and over again, searching for bad connections and components.
What I´ve found so far is;

If I pulled the first tube I don´t get any noise, the amp is quiet.
With volume and master open and Tone closed, I don´t get the hum or hiss.
If I touch the heater wires between v1 and v2 i can hear it through the speaker, the first tube and all the wiring is very sensitive to touch.

The amp is perfect if I don´t open the Tone control past 2 or 3.

I´m going to do it all over again.

[Phil_S]

If I pulled the first tube I don´t get any noise, the amp is quiet.

I think this tells us the problem is with V1. Don't touch anything that isn't connected to V1.

If I touch the heater wires between v1 and v2 i can hear it through the speaker, the first tube and all the wiring is very sensitive to touch.

I believe you have found at least part of the problem. Try removing that part of the filament wiring. Install a new twisted pair that runs on the floor of the chassis and in the fold at the rear wall. Like this, near the bottom of the page http://www.valvewizard.co.uk/heater.html

The amp is perfect if I don´t open the Tone control past 2 or 3.

Sure. It's an amplifier. As soon as you get to 2 or 3, it amplifies the hum.

[luistrindade83]

Just to update on the situation... hum is now on acceptable levels, but I’m experiencing oscillation.

The problem is the treble control, I can only dial it till half. After that I get oscillation on the master and volume, around 80 or 90%.

Any advice?

[T Wilcox]

What did you do that lowered the hum to acceptable level?
Most oscillation problems I've dealt with (other than reversed OT primaries) are due to poor layout in the input section. The wire going from your input jack to the V1a grid is like an antenna. I use rg174u coax for all my input runs these days. Your grid stopper should be soldered directly to the tube socket grid with very little wire lead between the resistor body and solder point. Run coax with shield ground "ONLY" on the input jack side and terminate at your grid stopper.

[luistrindade83]

I change the heaters wiring, followed Phil advices and arrange them like seen on the link he sent me, the hum dropped to acceptable sound, only in real loud volumes is that is heard.

I’ll give it a try on the coax cable.

[TUBEDUDE]

If manipulating the wire causes crackling you have a bad connection. Touch up your joints, especially the grounds.

[luistrindade83]

First of all let me thank you all, the problem seems to be fixed.

I’ll post some pics for you guys to see, I’ve wired the heaters against the back of the chassis and kept the leads short.

The amp is now working fine, no oscillation and a normal hum on high volumes.

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[luistrindade83]

Hello,

Just to inform that the problem of hum was fixed but oscillation came again and I had to do some alterations to the layout.

I’ll share what fixed my problems:

Moved the v2 away from the v1;
Sold the grid stop resistors directly on v1;
Install 500pf snub caps.

I’ll share some photos. Thank you all, really.

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[luistrindade83]

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[Colossal]

So how are you liking the tone now that you got the amp sorted out?