new Express build problems

[Gibsonman63]

I had an interesting issue with my Liverpool this week. I finished my cabinet and installed the chassis. The amp lost a lot of power and sounded very tinny. I figured out that one of the lugs from the bass pot was too close to the chassis where it folds over. Once I mounted it in the cabinet and snugged it down, it was just enough pressure to short out.

[Randy Magee]

On my original Express at one point early in it's life I sometimes had some slight oscilation issues. The fix at the time was to put a small piece of foam under the edge of the power supply board to keep the OT primary wires down against the chassis. These days however the amp has settled down and the foam is gone but the wires stay put. That said, in your amp it appears your primary wires are quite a bit longer than on my original, and route back towards the rear panel then up towards the board and OT. Also you have your high voltage runs terminating under the power supply board. I'd try rerouting your B+ leads like on an original which are elevated over the board and tie to the tops of the terminals at the group of power resistors. Then I'd reroute your OT primarys to be shorter, with a slight loop or two and running more direct. On my original the OT primarys run under the PS board about have the way up, and the OT secondaries come out of the transformer towards the rear of the chassis. Perhaps you have some instabilities due to non original type lead dress in these areas mentioned. Like I said, my original was tempermental specifically in the lead dress of the OT.

Your points are well taken, Glenn. I left the primaries off the OT long intentionally in case I had to swap them with the intention of shortening them later when I was sure the polarity was right. It not that I have noise, I just am not getting the volume this beast should have. I know it's something simple that I just haven't come across as yet...

[dmouse]

which jack are you plugging your speaker into?

[dmouse]

which jack are you plugging your speaker into?

[Randy Magee]

which jack are you plugging your speaker into?

The first in the chain from the impedance selector...

[dmouse]

your black wire from the output transformer goes to the groung on the speaker output jack, which is also grounded to the chassis? I think it has been asked before only one of your output jacks the tip is grounded correct? I had a similar problem when I first fired mine up. Both of my output jack tips were grounded, I just clipped the wires to the second output jack and I had output.

[Randy Magee]

dmouse, I didn't use a jack with a grounded tip in either position.

[Gibsonman63]

I am thinking that it has to be in the signal path somewhere. Otherwise your voltages would be off... and it would be easy to find.

[don280z]

...on the EL34's....are pins 8 & 1 tied together? I don't see any ground connection on pin 1....

[Randy Magee]

...on the EL34's....are pins 8 & 1 tied together? I don't see any ground connection on pin 1....

The grounds run to some external bias point pins...

[Randy Magee]

I've tried swapping the leads from the OT primaries with no joy... lifted the negative feedback with no change... I'm trying to find a 1/4" to RCA jack so I can use the sound card on my computer to generate some noise for the audio probe I made... it gets more curious all the time...

[Randy Magee]

I checked every resistor and capacitor on the board and those connected to the pots and tube sockets and they all check out for proper values...

[M Fowler]

I take it that the blue wire going to the 220k resistor on the board is connected under the board? Circled

The white wire is connect from the top of the board?

Mark

[Randy Magee]

Mark, yes that's the situation... I'd made a wiring mistake... at first both wires were connected under the board... when I fired it off and checked the bias current, I discovered the mistake, clipped the mistake off and rewired to the turret from the topside to keep from having to remove the board... I'm about ready to throw my hands up on this one...

[M Fowler]

I thought that might be the case but I was hoping for an easy fix for you.

This is when it would be nice to live near another TAG member like I do.