Express some little issues.....

[redshark]

I completed my express around Xmas. It sounds great will all knobs at noon. Gives me great sounds from clean to mean. reading some of the late threads about oscillation in express I learned that so far I didn't tested it fully and I had become more curious about this issues. I unplugged the input cable and maxed out the volume and I noticed that at full volume it starts giving me a high frequency noise (past 3 oclock), maybe is the hiss getting bigger?
Do I have an oscillation problem? is this normal? Also does kinda the same thing with presence maxed out. I know that I won't be playing it at full volume so I shouldn't care but I rather be sure...opinions?

[Cliff Schecht]

Past a certain point the hiss builds up and bleeds into the amp enough to cause some major noise problems. Mine gets pretty ridiculous when the presence and/or treble knobs are maxed but it's really more of a loud hiss than an actual oscillation. The noise is something that you really just have to deal with either by keeping both of these controls low (I'm sure most people don't turn the treble or presence up very high on a "stock" Express build) or modifying the circuit to reduce the bandwidth and kill this noise. I like the first approach better, I did the second approach on my first amp and I really feel it's lacking in the gain department because I neutered it a bit too much.

[paulster]

That sounds like you're getting tube microphony, which is quite can be one of the trickier things to tame with these amps.

Try swapping out your V1 tube and see how it goes, as you can often have to go through a stash of tubes to get a quiet one that sounds fantastic.

[passfan]

I got some tung sol reissues from AES and microphonics are a thing of the past for my express. All I get is hiss , and I can knock on the chassis and not hear it , so it's possible.

[redshark]

Yes, I already went through a bunch of tested good NOS tubes and I have a feeling is not the problem. I think it has to do with wire placing, just moving the wires that go to the bass pot to correct francesca layout gave me a little bit more harmonics but more gain as well. I had them placed like cliff in his thread pics but noticed that and moved them, not sure how I like them more. I noticed that when I open my volume control all the way in the guitar of course the amp goes to feedback but I notice some big vibration not fully perceptible on the ear(lower volume) while on feedback that could be a parasitic oscillation but just changing my position to the cabinet corrects it, kinda strange. This amps run so close to being unstable that sometimes is hard to figure out this things, also that vibration thing must have something to do with the speaker cab being on top of hardwood floor and having windows around it. Maybe time to move the rig somewhere else to test.

[passfan]

Yes, I already went through a bunch of tested good NOS tubes and I have a feeling is not the problem. I think it has to do with wire placing, just moving the wires that go to the bass pot to correct francesca layout gave me a little bit more harmonics but more gain as well. I had them placed like cliff in his thread pics but noticed that and moved them, not sure how I like them more. I noticed that when I open my volume control all the way in the guitar of course the amp goes to feedback but I notice some big vibration not fully perceptible on the ear(lower volume) while on feedback that could be a parasitic oscillation but just changing my position to the cabinet corrects it, kinda strange. This amps run so close to being unstable that sometimes is hard to figure out this things, also that vibration thing must have something to do with the speaker cab being on top of hardwood floor and having windows around it. Maybe time to move the rig somewhere else to test.

You know when I installed my pec pots the second time around one of the things I did was to run the blue and yellow leads coming off the bass pot down in the chassis corners under all the pots and over to the turret board. The first time I ran them up high about board level right down the centerline of the pots and then to the board. I also went from a fender style switchcraft jack to a cliff jack and grounded it direct to the buss. The changes I've made and the problems I've had and overcome have been in the pot , ground buss area. I've yet to deal with an issue outside of that area in one of these amps.

[redshark]

Yes, the express is very temperamental. I just went and played it with an even higher output guitar and it was fine. No doubt you need to control this amps. My preamp tubes sound great, the ones that I use for V1 2 ecc83 old mullards which are not noisy but I notice they have a gas problem because when I hit the switch on they flash and it's just the heathers coming. Once standby on they sounds great, very warm tubes.

[passfan]

Yes, the express is very temperamental. I just went and played it with an even higher output guitar and it was fine. No doubt you need to control this amps. My preamp tubes sound great, the ones that I use for V1 2 ecc83 old mullards which are not noisy but I notice they have a gas problem because when I hit the switch on they flash and it's just the heathers coming. Once standby on they sounds great, very warm tubes.

I researched that once and it's not a gas problem it's temperature. Some tubes when the element is cold they flash initially before they warm up. If you shut it down and then turn it back on before they cool they won't do it. I have a pair of EI's that do this everytime (when cold). Keep using them.

[paulster]

Mullards are supposed to flash at turn-on. It's one way of telling genuine ones! Don't write them off because of that!

[redshark]

Thanks for the info!!! I always though that the preamp tubes that flash were on their way out which doesn't make any sense because these mullards test like 58-62 with 32 as minimum.
Good to know I guess the huge feedback and vibration with the guitar volume maxed out is the way this amps perform, so close to be unstable, maybe that is how they show it!!
I know that the topic of what tubes are better for the express has been discussed a lot and that Ken prefered tungsram and EI but I think mullards sound sweet, they are very warm. I still use a tungsram for the PI but Mullards give it that woody tone.

[redshark]

This amp is really strange, seems everything on a wreck gets exagerated. Moved some wires, twisted together the OT primary wires, reflowed some joints in the volume and treble controls and the oscillation only happens now with everything maxed out and the volume control almost on 3oclock before that just a lot of hiss.
Now when I played it again with all controls at 12 noon the amp is more harmonically rich but cleaner, not as distorted as it was before, and A LOT LESS noisy...uhm, so that means that the more stable it is the less gainy ....am I right?

[passfan]

This amp is really strange, seems everything on a wreck gets exagerated. Moved some wires, twisted together the OT primary wires, reflowed some joints in the volume and treble controls and the oscillation only happens now with everything maxed out and the volume control almost on 3oclock before that just a lot of hiss.
Now when I played it again with all controls at 12 noon the amp is more harmonically rich but cleaner, not as distorted as it was before, and A LOT LESS noisy...uhm, so that means that the more stable it is the less gainy ....am I right?

I wouldn't use the term gainy , I'd say you just backed away from the edge of the cliff. You can still give it that trebly sound with the presence but it has just as much gain , and it's stable now and the junk, so to speak, is gone.

[redshark]

I wouldn't say it's completely gone, it just happens now when I dial in extreme settings that I will probably won't use (all controls maxed out and no guitar cable plugged in).
Today I will test it even more. I think it was a mistake that I never did this testing just because in playable settings and conditions it sounds fine, maybe a little bit much over the edge but still controllable.
What I've always found interesting is that no other of the owners of originals except for Glen Kuykendall has made a demo of any trainwreck amp. Well, I think there's one Liverpool and one rocket demo but that's all. So we don't have much evidence of the real thing that we can use to compare our clones.

[redshark]

silly me, didn't know you don't measure ac to ground

[passfan]

silly me, didn't know you don't measure ac to ground

I don't get the context , what am I missing. How else would you measure ac ?