Trainwreck Express Build

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 4:41 pm

In that case I'll leave it there, it might be a carbon comp I'm not sure but I don't think I added any extra noise so it can stay. I'll add a 10K to V1A to help with microphonics. I'll also left that 1K resistor if I can as it did get a bit hot after 20minutes of playing. Wasn't scalding hot but better safe than sorry.

There is still a bit of buzz but that might be the wiring in my room as my Marshall buzzes a bit.

M Fowler · Post by **M Fowler** » Sat Mar 08, 2014 5:07 pm

Also, try different guitars and cords.

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 5:47 pm

My brother has a Telecaster so that will be a pretty good test!

Just raising the 1K Resistor at the moment, replacing those solid core wires for the B+ with insulated wire and moving the Heater CT.

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 5:53 pm

Do you think I should ground my Heater CT at the 40x20x20x20 Ground point? It'll be closer to the first Output Valve then.

M Fowler · Post by **M Fowler** » Sat Mar 08, 2014 6:00 pm

Ground it with the HT CT or 50/50 cap ground.

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 8:49 pm

Right made few changes. Raised the 1K resistor, moved the Heater CT to the PS Ground Lug, replaced thd solid core wires for the PS with insulated wire. Did some more tube swapping and the amp is quieter now. I still get a buzz even with nothing plugged in but that might be the wiring here as my Marshall has a bit of a buzz as well. I'll post pics up in a bit.

Now after playing through the amp for a bit I have noticed that its very responsive to whatever you put into it. Much better than my Marshall, lovely harmonics and its the first amp that really took to my Wah Pedal! The Bass, Mid and Presence Controls don't seem to make a world of difference but then again with these amps I think its more about hearing the character of your guitar. Getting my brother to try his guitar through it tomorrow to see what he thinks. Also going to get the scope on it tomorrow to check it again.

Anyway I wouldn't of got this far if it wasn't for you guys, so thanks for all your help. Learnt quite a lot over the last few days!

Tillydog · Post by **Tillydog** » Sat Mar 08, 2014 11:56 pm

Glad to hear you're getting there!

Littlewyan wrote:O btw the issue with the volume going quiet when on full only happens when all tone knobs are turned to 0 so I guess thats normal. Doh!

Doh! indeed - I should have spotted that...

tictac · Post by **tictac** » Sun Mar 09, 2014 7:44 am

That 25W resistor is designed to be mounted on the metal chassis which acts as a heatsink. Otherwise it's a 5W resistor....

Littlewyan · Post by **Littlewyan** » Sun Mar 09, 2014 9:07 am

It should be but I have no where on the chassis in that area to mount it

Littlewyan · Post by **Littlewyan** » Sun Mar 09, 2014 9:18 am

Here are the pics as promised. Hopefully I'll get it into it's cabinet today.

Littlewyan · Post by **Littlewyan** » Sun Mar 09, 2014 9:28 am

More Pics

Littlewyan · Post by **Littlewyan** » Sun Mar 09, 2014 9:32 am

Heres some pics of me wiring it up. I'm afraid there is a bit of a jump between photos as I forgot to take some when I was part way through!

Littlewyan · Post by **Littlewyan** » Sun Mar 09, 2014 9:46 am

Right I checked the 25w resistor and those chassis mount resistors are rated at 12.5W in Free Air. Now I'm going to see if this one gets too hot for my liking, if it does I'll try to mount it on the chassis. I think I can see a spot where I can drill through to mount the resistor and if I get it right I could mount it using both holes

Littlewyan · Post by **Littlewyan** » Sun Mar 09, 2014 3:59 pm

Ok guys the buzz is annoying me. Now lets think about logically. There is no buzz with all knobs on 0. If the tone controls are on 0 and I turn the volume up I get buzz until the volume is on full. This is because on full volume the grid will be at ground due to the tone controls. So its got to be between the volume pot and the grid as wouldnt this take the V1B Anode put of the equation?

I'm thinking its either that 2.2k grid stopper on the grid or its that heater cable that goes beneath the anode and grid on that side.

Edit: In fact I'm sure its that Heater Wire, as that would make complete sense. I'll move it tonight over the top of the valve socket

Tillydog · Post by **Tillydog** » Sun Mar 09, 2014 6:33 pm

If it's quiet as you describe, then the grounds are good. It could be noise from V2 heaters leaking in or the lead between volume pot wiper and V2a grid picking something up (maybe from the heater lead, a you suspect).

You could try an artificial centre tap (fit 2 x 100R resistors across the heater supply and ground the junction instead of the heater winding CT) or a 'humdinger' pot.

I would vote for elevating the heaters, but that means finding a little space for a few more components.

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