My first build, What should I do before thuning it on?

[M Fowler]

Mont I had Nik build me an Express a few years ago and yes he doesn't connect the third lug to ground. Others do.

Mark

[Mont]

Thanks...

[jaysg]

Pull all the tubes and verify the power supply first. Then add preamp tubes...verify that they light and that the 6.3V stays put.

[Mont]

Plugged it in with the bulb limiter and everything checked out. I set the bias pot so it reads -33 volts onpins 5 of my out out tubes. power down, plug in tubes and the amp light does not come on and the limiter bulb is glowing bright. any advice?

[geetarpicker]

You wouldn't want to adjust the bias to any set point yet, as with the inline bulb the power coming in should be lower than normal and that throws off the measurements just yet. Typically you would set the bias trimmer all the way up voltage wise for starters. That would be running your power tubes at their coldest point for starters.

That said, others may be able to help from this point as it sounds like you have a dead short somewhere. Hard to guess but at this point DO NOT put full line power into it until this issue is tracked down and corrected!

When you tried it without tubes did you have both the standby and power switches ON?

Start checking your work. Also do your best to confirm that the subterranian wires are correctly connected under the boards. You might also check that your board terminals don't short out underneath with any mounting bolts like those holding down the OT or PT.

Don't feel bad. Even Ken made a mistake in my original Express. He had the wires going to the green 1k power resistors on the ouput tubes on the wrong end of each resistor. That effectively bypassed each resistor, making the amp a little harder on tubes. Still it sounded great that way but I talked to Ken about a year after owning the amp and he said yep, that's a mistake better move the two wires.

[geetarpicker]

A hi resolution pic might help to!

[Greg]

This is too funny. Really Glen, great picture.

I got to tell you guys that I was in the exact same situation...I was so darn nervous to actually fire it up...It all worked out real well. Thanks of course to the gang here at TAG.

[Greg]

Fire pic...that is

[marcoloco961]

A hi resolution pic might help to!

+1 on the pics

A good series of gut shots would help someone troubleshoot the problem for you. I would start looking at all points where any high voltage DC could short to a ground on the chassis, etc. Double check all tube sockets well for stray solder or flux residue / carbon trails. Was the indicator light on before tubes were installed??

Also, not that it matters to your immediate problem, but as Glen said, adjust the bias all the way to the most negative value possible before tubing again. Probably in the - 45 to - 50 volt range.

Be patient, you will get it going. I haven't seen a problem arise yet that the folks here have not been able to help fix.

[geetarpicker]

Wouldn't you want the highest bias voltage at start up? Doesn't higher bias voltage actually cause the tubes to draw less current? Correct me if I'm backwards on this, it's been a while since I measured bias voltage.

[paulster]

Coldest bias is most negative, so you want the highest negative voltage you can get.

Hottest bias is when you have no bias voltage applied, so closest to 0V. That's not where you want to start with nice power tubes!

[Structo]

Uh yeah, turn the bias down before starting it.
I'm not sure I know what is going on?

First you fired it up with the limiter and it was ok then you fired it up and the bulb stayed bright?

Be sure to have a speaker load connected to the amp if you have the power tubes installed. (Better for the OT and tubes you know)

[Ron Worley]

No, it is NOT correct. If the pot fails, your bias will cause the tube to go to max current (red plating, explosions, fire, mayhem, death)...

Look at the layout in the latest build guide and you will see that the middle and one outside lug are tied to ground (if I recall right). Pot fails, min current, no problem......

The Ceriatone layout is not correct for this...

[Mont]

OK, I hope I found the problem. on the ceriatone layout it is not clear that pins 6 of the output tubes connect to the 25 watt resisstor on the ps board?

[paulster]

What might help you look at this with a fresh perspective is to download Ron's layout (and build guide) from the Trainwreck Files section and tick off everything on the layout against your amp.

Ticking it off ensures that you actually study each component, wire and joint rather than making the mental leap of faith that 'it looks right'! It's amazing the difference that simple exercise can make.