An Express is born, but it's sick

[Wayne Alexander]

I finally got my express all together (a1a except I added the "simplest master volume ever" from the post below). When I first turned it on it was blowing fuses, that turned out to be that I'd wired a fender-style 6.2v indicator light to the 120V tap, and I had the B+2 wire to ground where it joins thetwo 1meg resistors that go to the grids on the EL34's. After that was fixed it didn't blow fuses, but still wouldn't make a sound. I went through every component and wire and compared them to the schematic and layouts, of course I found a few incorrect resistors and one unsoldered connection on the component board. After fixing everything I could find, I turned it on again. No noise at all without a guitar cable in it, but with a cable and guitar plugged in I've got a lot of what may be blocking distortion and shrieking. I once built an amp where I put the output wires from the OT under the main component board, this sounds like that - a shriek above everything, and an overall very distorted character to the sound, and on this amp there's only about 1/6 the volume I'd expect. It sounds like Eddie Van Halen but with a lot of nasty oscillations and things over it, and it won't play even remotely clean, and it's no louder than an unmiked human voice. After moving wires around I didn't find anything obvious, so I'll try again next weekend. Do any of you have any particular suggestions? PS: my heater voltage seems to be 6.87V, the 300V taps off the PT put out 301, my B+1 voltage is about 409, and the B+2, 3, 4and 5 step down about the amount expected (I didn't do the math but they seem about right).

[Allynmey]

Hi Wayne, HeeBGB and I are in the process of building the same layout. We should have the things together next week. In the meanwhile, we followed the A1A Schematic and are using the layout in the files section for the preamp board. I used the tagboard layout by Snide, but, ran into space difficulties using the standard express chassis size. We are in the process of building new power supply tag boards for the build. Do you have a layout drawn to help see how you put it together? If so, did you follow it exactly? Post or e-mail me the layout or some pics to see what your doing and maybe we can find a fix. Without a layout or pics it's impossible to see what you might have done wrong.

Allynmey

[ampdoc1]

Wayne,

I originally posted the "simpliest MV ever" file. Have you checked the feedback on that thread? One guy wired his phase inverter exactly per my diagram (which has the signal input to pin 2), even though he used pin 7 as the PI input stage. He was also getting very low volume. Just a suggestion! Good luck.

David Hicks

[Wayne Alexander]

Allynmay and Ampdoc1, I followed the A1A schematic exactly (I think, mistakes are possible) with two exceptions - I put a 10 ohm power resistor across the switched lugs of the first speaker jack, so there's a load there with no speaker plugged in, and I tried the "Simplest Master Volume Ever". I may try shielding the wires for that, if I understand it correctly, they'd all count as grid wires.

It's going to be another week or two until I can get the time to work on it again, if I can't get it running right I'll post pictures. (I'll also post a couple if I do get it running right.

I ran into huge space issues in trying to fit all the filter caps onto any of the layouts I've seen for the power supply board, so I made a huge one that takes up a lot of real estate on that side of the amp. I didn't cut all the unused transformer leads short (5v taps on the PT, the alternate set of secondaries on the OT), just zip-tied them and taped off the ends, which are all under various parts of the power supply board. Would that be a source of noise/power loss?

[Guest]

I find it odd that so many here want to try their hand at an Express clone, yet don't understand the basics of tube circuitry.

Look at most of the questions, they scare the hell out of me. Someone's gonna get hurt.

Like watching some guys trying to build a race car while still learning to tell a spark plug from an oil filter.

[Wayne Alexander]

After spending another couple of hours trying to find the problems, I found that the resistors between B+2 and grid 2 on the power tubes (pin 5) were 1 meg instead of 1K. After fixing that, and using shielded wire for the master volume wiring (not sure it was necessary but it seemed logical) it runs. It's VERY LOUD, and it's got some hum that may or may not be an issue (the power in my basement is pretty dirty, will have to try it with a better outlet). Also, the chassis itself is slightly microphonic- it rings when tapped. I also may want to change some cap values to make the amp a bit bassier overall. But the main thing is, it works. I posted pictures over in the "How about we post some pics and layouts?" thread.