New Express Build

[Tone_Chaser]

I build amps, guitars and pedals and don't have a lot of time or money to dedicate to any one hobby. This means that my builds are really slow. The Express build has been no different.

I finished it tonight and started the power up with a bulb limiter using the instructions in the build document and ran into something strange. I ordered the switches using the part numbers from the BOM and the power switch is a 3 position switch and the pilot light is on no matter what position the switch is in.

I thought I'd go ahead and check some voltages so I put the tubes in and plugged it in and the fuse blew right away. I need to pick up some fuses tomorrow and start going through the wiring again and see what I can find. Of course I only had one fuse in the house!

I am still working on the cabinet. I have the main box complete but am looking for a good match for the valance and frame. Hopefully that will come together pretty quickly.

Once it's all good to go, I'll post some pics. I may have to end up getting a new switch to get it to work right. Looking forward to getting to play this amp!

[DaveMon]

With all the radio shacks disappearing.......needing a fuse can be a big deal!! Looking forward to seeing and hearing your amp!!

Sent from my SM-N960U using Tapatalk

[M Fowler]

You can buy fuses at big box stores Menards, Lowes, Home Depot, under time delay fuses for a slow blow type.

Electrical distributors also sell fuses at their City Desk for non-contractor accounts.

I usually just order from www.CEDist.com or www.Mojotone.com

Hoffman Amps. com also sells fuses.

Mark

[Tone_Chaser]

I wish I had seen this before I went shopping yesterday. I used to get them at RadioShack but that's no good anymore. I needed some things from Valvestorm anyway so I ordered some. If I get back to town before they come in, I'll pick some up.

Thanks!

[Tone_Chaser]

I did end up getting a different switch and that worked out better, but I ran into some issues with the turn up and kind of just set this aside for over a year. I decided to get back to it and started the turn up procedure.

And it failed the first step!

Going by the document, it says to find the maximum negative bias voltage (between -35 and -50 using EL34s). Mine is -12.7, less than half of what it should be. If it was close but low, I wouldn't worry about it, but that's too far off.

Does anyone have any thoughts or ideas? I'm going to go over the power section one more time. I checked a few other voltages, my heaters are 6.7, at this location my mains was at 118 and the secondary was 610. My B+1 & 2 were about half of what they should be and 3-5 are almost 0 volts. There has to be something wrong there. Will go through the wiring and connections tonight to see what I might have done wrong, but would appreciate any ideas on where to focus.

Thanks!

[M Fowler]

The trick for most toggle switches for the Trainwrecks is wire the incoming AC mains wiring to the middle of the switch and transformer/amp power section to what ever end of the switch opposite the direction the switch bat is facing. So in a TW amp we switch up so then the bottom of the switch is the on position. I mostly us DPDT six solder lug switches except for the Standby which is SPST type.

Using the two solder lug Fender type switch creates too much extra wiring and not traditional to TW amps.

Not sure any of this helps you, you could take some high quality photos and post for us to look at and then we could better respond.

The power switch in the layout below is wired correctly.

Mark

TWEXPRESSLAYOUT.pdf

[Tone_Chaser]

Thanks. I'll try to get some pics uploaded this weekend. That's the layout I've been following to check my wiring.

I did find two bad solder joints and fixed those tonight. I think that someone doesn't want me to finish this amp. I broke one of the power tubes removing it earlier today when I was starting the start up.

[stringtuner]

I'm curious to learn more. Did you fix the start up issues yet?

I'm searching for a chassis in Aluminum. Any ideas where I can get one?

Cheers, Don

[wpaulvogel]

I’ve got some chassis. I sent you a message.

[Tone_Chaser]

Finally pulled the amp back out to try to get it going. Went through the first steps again and ran into the same issue after going through the power supply section and re-flowing some of the solder. The max negative voltage on pin 5 of the power tubes is about -12.7V. The other voltages look pretty good moving on through the startup. I kind of forgot about the power tubes, so I'll have to get some before doing the full startup. I'm adding some pictures to see if any of you can see anything I'm missing. Sometimes another set of eyes are what's needed.

[Tone_Chaser]

I just found that the DV voltage of the center pin of the trim pot varies as you adjust the POT from 0V to -12.3V but pin 3 is 0V. Pin 1 is always -12.3V. Pin 2 and three are both connected to ground so shouldn't they both be 0V and pin 1 should vary when you adjust the POT?

[joeboo88]

I think you have your bias resistors wrong?
You also have a 1.5 k resistor? Was that what you needed?
Usually a 15 k resistor goes between the caps where you have the 47k.
where you have the 1.5k you would implement the 47k resistor at the trimmer. Are those bias caps grounded? I can’t see it.
All of that Might be why you get weird voltages
Also you might want to look at your your solder joints, I believe you will have problems in the future with the way they are.
Look at the schem/layout..... good luck

[wpaulvogel]

Yep, you need a 15k brown red orange between the bias caps and move the 47k to where you have to wrong 1.5k

[sluckey]

Yep, you need a 15k brown red orange between the bias caps

I believe that would be brown green orange.

[Tone_Chaser]

Thanks guys! I hoped some fresh eyes would do it. I'll try to get those fixed and check it again. I can't believe I messed those up. You think you're being careful as you go through the build but it's easy to make a mistake.