Trainwreck Express Build

[Tillydog]

I would try moving that red presence wire well away from the tonestack wiring (blue + yellow wires) and see it it helps with the 'going quiet'.

Also, the soldering between the busbar and the pot casings doesn't seem to have taken. May not be a problem as the pots are grounded to the chassis, anyway.

How have you wired the PSU cap grounds? (I can't see from the photos.)

[Littlewyan]

Presence Wire didn't make a difference and the busbar is very secure as I can give it a good tug with the pliers, plus I checked it with my ohmeter. It does look like a ground issue though as if I touch the back of the volume pot with my pliers then I can hear a noise through the speaker. Surely I shouldn't get that if the pot is grounded?

[Colossal]

LW,

Yes, you might consider pouring over some of the Express photos and consider the tone stack leads and shortening/changing your dress as needed. The area around the Vol, bright caps, and Treble is sensitive. Others have reported big changes in the amps' response with placement of that treble lead!

[Littlewyan]

Yes i might admit that my Tone Stack leads are a little long. Will take a look at some pics and will then redo them. Name is Ryan btw .

[Colossal]

Yes i might admit that my Tone Stack leads are a little long. Will take a look at some pics and will then redo them. Name is Ryan btw .

Good that they are long as that will, at least experimentally, let you chopstick them around to see which one(s) have any effect, as well as give you some material to trim and refit. Good to meet you. Looks like a nice build. Should be deadly when you get it sorted.

[Littlewyan]

Well the only one that seems to have any affect is the treble wire. I'm also going to try increasing the size of the grid stopper on V1B to 10K to see if this has any affect.

EDIT: Tried putting a 47K in series with the 2.7K grid stopper, this helped a bit but didn't fix the issue so thats one thing off the list. Looking at a few pics people have put the treble wire down to the chassis so perhaps thats what I need to do.

[geetarpicker]

I know this sounds crazy but you might even try removing the shielded cable going to the 2nd stage. The original TWs got away with just one shielded cable from the input to V1, and no where else. In my experience sometimes (in high gain tube circuits) shielded cable can actually cause problems.

[Littlewyan]

I did try disconnecting the shield but that didn't make much difference. But I guess a floating shield wouldn't help either so i'll try replacing that with a pvc stranded wire.

Edit: Btw I made the treble wire longer, pushed it against the chassis and that helped a bit.

[geetarpicker]

I'd suggest following the lead dress of an original more closely. You might shorten all those ground leads to the pots, as on an original they are all less than an inch long though your board is farther away. Also the two long wires on the bass pot are tucked down in the front corner edge on an original. You might also experiment with the orientation of the bright caps and switch. You have the caps tied together coming off the end terminal on the volume pot, though some amps are more stable with the tied caps coming off the center terminal instead. Some report this can effect the stability even when the bright switch is in the off position. In the end you should be able to dime all the controls with full stability, though at that point preamp tubes have to be quiet in regards to microphonics. Keep in mind the amp might not be fully stable until a metal ground plate of some sort is covering the open side of the chassis.

[Littlewyan]

Wouldn't the caps only affect the amp when switched on though? I'll shorten all of my wires as much as poss

Update: Shorted the treble, mid and bass wires by at least an inch each and that has helped a lot. Also shortened all ground wires a lot, just ran them going direct to the ground bus wire so they're all floating. Also shortened the Presence wire and pulled it away from the bass and mid wires a bit more. Just got to change the shielded cable for a pvc stranded yet. Interesting about the caps Glen, will have to look at that. As for the plate I'm going to staple an aluminium sheet to the bottom of my head cabinet like Marshall do.

[Littlewyan]

Right I've used a thick stranded wire for the Volume Pot with a 2.2K Grid Stopper this time but still same issue, nothing has changed. The Tone Controls don't really affect the noise anymore though since I shortened their wires. So now I'm going to try shortening all the anode, cathode and grid wires and perhaps try like a 100K Grid Stopper just to see if it helps at all.

[Jackie Treehorn]

The way the input jack is wired doesn't seem right to me?

Yes, doesn't look right to me, either...

[Littlewyan]

Whats not right about it? I've checked it and it works as it should, grounds the jack when nothing is plugged in.

Update: 150K Grid Stopper did nothing to stop the issue. Checked again with my oscilloscope and it definitely comes from the volume pot.

[Colossal]

Can you check your V1b cathode bypass cap for leakage? Also, can you try rotating the yellow lead connecting the bright switch to the volume pot up and away from that shielded lead going to V1a.

[Jackie Treehorn]

Whats not right about it? I've checked it and it works as it should, grounds the jack when nothing is plugged in.

Update: 150K Grid Stopper did nothing to stop the issue. Checked again with my oscilloscope and it definitely comes from the volume pot.

Yes, I guess it works. It's the 1 meg resistor, it looks like it's connected between two points on the tip rather than tip to sleeve, but once a cable is plugged in, it should work as is. Just looks strange.