Newbie problems with startup!

[Matt J]

Hey everyone,
I just finished my first TW Express build and I'm going through the startup procedures listed in the Express Build Guide and I'm coming across some problems and was hoping some of you would have some advice. The PT and OT and Pacifics from RJ guitars (who has been extremely helpful throughout all this!) as where most of the other parts you see. I built the amp through guides and tips posted here on the forum and pictures of Francesca. When going through the start up procedures I am using a Kendrick Bulb Limiter with a 25w bulb. I did make sure a 2 Amp slo-blo fuse is installed. Without the tubes installed, and with the amp hooked up to a cabinet, when I turned the amp to standby the bulb did light up and dimmed, pilot light came on ok and I was able to measure out 6.79 vac between the heaters, measuring between the heaters and the ground only got me 3.3 vac. Setting the max negative bias I measured out around -34 dcv on pin 5 of V5. On switch, PT secondaries, filter caps, B+1 through B+5, and plate voltages all came out ok. They were lower than what you would expect because of the bulb limiter. When I measure for negative DC on the wiper of the bias pot the reading was 0 though. When I moved on and installed the tubes, I used electro harmonix for both the EL34s and 12AX7s just for the start up process. All the heaters lit up with the amp in standby but once I went from standby to ON the bulb limiter lit up and did not dim. I turned the amp off and discovered the fuse had blown.

I wondered if a problem had arose with the bias trimmer pot when I installed it since I measured no negative voltage on the wiper so I replaced the pot with another 25K linear pot. Beginning the start up procedures again without the tubes I measured a -46.1 dvc on pin 5 of V5 for the max negative voltage. Now, when I turn the amp from standby to ON, the bulb limiter lights up and the fuse blows.

I have been retracing my steps while going over the layout and schematics, being as methodical as I can. I took a lot of pictures while I was building the amp. I am including several pics of the power supply area as I put it together.

Does anyone see any noticable problems from the photos? It may just be something I have overlooked. This is my 2nd build overall so I am still quite new to the amp building world.
Thanks!
- Matt J.

[Matt J]

More photos.

[labb]

Double check the polarity of C21 and C22. Looks like they are correct but that is a good place to start..Remove you pre amp tubes and just check the Power Tubes and see if you can pin the problem down to which section.

[KellyBass]

The standby switch looks odd to me. I think the OT center tap wire and the wire to the cement resistor should share the same pole.

[marcoloco961]

Are your 3 diodes on your power tubes backwards. Looks like the line should be away from your ground. From the pic I saw they look wrong.
i think that might blow a fuse.

[Matt J]

Thanks!
Yep, I just looked at the diodes on V5, they were backwards. I fixed the standby switch too. I flipped the diodes around, set the amp to standby without tubes in, everything came on ok with the bulb limiter. Turned the amp to ON, bulb limiter dimmed and the fuse did not blow. I'm going to check over it some more tomorrow after work, measure out some more voltages and continue with the start up process.

[marcoloco961]

Thanks!
Yep, I just looked at the diodes on V5, they were backwards. I fixed the standby switch too. I flipped the diodes around, set the amp to standby without tubes in, everything came on ok with the bulb limiter. Turned the amp to ON, bulb limiter dimmed and the fuse did not blow. I'm going to check over it some more tomorrow after work, measure out some more voltages and continue with the start up process.

Your welcome. I got lucky. Clicked on the first pic, enlarged it, and the diodes just kinda jumped out..and I thought, (hey, that might blow a fuse) ...LOL.
Very nice looking build BTW. Nice work for your first couple attempts at amp building. Keep up the good work.

Good luck on the rest of your testing tomorrow. You are officially "hooked". These amps are like tattoos.....nobody has just one. So what's next? A Liverpool, a Rocket maybe??

[ampmike]

Hey Matt,Hang in there,Your work looks nice and neat!These guys here are great and they will get you through to startup.I went through this a couple months ago.But went you fire up, you will be in your glory!!!Good Luck Man PS,I did the same thing with the diodes

[tubedogsmith]

Not the problem you're talking about but you absolutelyh do not want your trannie wire coming throught the chassis in contact with bare metal. The edges of the holes will eventually wear through the wire insulation. I've cleaned up several home brews for people and two proffessional builds with this issue.

[TheGimp]

Rubber gromets are a pain but well worth it.

Also the yellow wires from the transformer that are sticking in the air would be best if the ends were covered with heat shrink tubing so they can not accidently short against something.

just minor clean-up.

[dobbhill]

The bleeder resistor's lead ( on the PS caps ) is awful close to the chassis. That'll blow a fuse, too....

[M Fowler]

Instead grommets I use nylon/plastic push throughs that I get from my local Hardware center they sit lower on the chassis and do not interfer like grommets do.

They come in various heights and diameters so suit to your needs.

[sunnydaze]

Might just be an in-process photo, but in pic #6, which is showing the + side of the power supply capacitors, looks like four of the six caps still need to be wired up.

[RJ Guitars]

Matt,

Thanks for posting this up. As you can see, you'll have some pretty good help available as you sort this out and then start tweaking it to your personal taste.

Do you have an update on the progress after wiring up the power supply filter caps?

You've given great pictures which are really helpful for sorting through the problems plus they will give others a great reference for the future.

Let us know how it's going,

thanks,

rj

[Matt J]

Hey folks, thanks for all the advice and comments! here's the latest update:
I fixed the diodes and standby switch. Everything fired up fine. No blown fuses, sparks or pops. I was worried too about the tranny wires coming through the holes. I could not find a grommet that fit the oval shaped holes. So what I did was smooth the edges of the holes down with a file and finally fine grain sandpaper. This smoothed them out so that there are no sharp edges. I also smeared a very thin amount of silicone glue (the same I used to build the PS cap stack) around the edges to act as a final barrier.

After going through everything with a multimeter, I added the tubes and began working from there. I'm still using the relatively cheap Electro Harmonix tubes for start up purposes. Since this is my first fixed bias build I don't want to take any chances with expensive glass when I'm trying to bias it. As for biasing, I used the Transformer Shunt method. Using the (.70x25 divided by plate voltage) I came up with a plate voltage of 391. So, .70x25/391 = .044ma. I kept reading that EL34s should be set between 40-44ma, so I set the bias trimmer at 44ma. After closely eying the tubes for a while I never saw any red plating.

The rest of the voltage chart is attached.

The 111v mains voltage is probably because my house is old and I'm in a rural area. I was confused where the chart says "secondaries" how would I measure this?

Well after biasing it up, I took the amp outside and hooked it up to a 1x12 amp cab with an M75 Scumback speaker so I could really crank it up and give it a test run. LOUD is the first way to describe it. I did notice that some of the preamp tubes were microphonic, there was a distinct high pitched rattling sound. I do not know if it is the tube itself or something with the wiring. As the amp goes into distortion there is a buzzing noise and it sounds as if the amp is farting out. Everything sounds very smooshed and rather unpleasant. Once again, it could be the tubes, but I was wondering if the plate voltages were too low, causing the tubes to distort too soon. How could I go about raising this voltage when I start tweaking the amp? Finally there is a background hum when the amp is on, irregardless if the the guitar is plugged in or not. It could just be AC hum, but I'm going to first try a 33k or 68k grid stop resistor to see if this quiets it.
My guitar has P-90s in it too, which break up early and produce a lot of background hum. I really want to try to smooth out the amp in the end. I know Trainwreck amps are designed to be hair trigger, but I would like to get some more headroom out of the preamp.

I have ordered some very nice tubes for when I get everything straightened out (and the cabinet complete), Siemens EL34s, a Telefunken 12ax7 with balanced triodes for the PI, a Mullard ECC83 and an Amperex Holland ECC83 tested for low microphonics,

I took a ton of pictures as I was building the amp, from start to finish. I'll post more of them up as I go along with fine tuning it.

Thanks again!
- Matt J.