The edge of instability......

[tubedogsmith]

To all the trainwreck experts....

is this the inside of a real wreck?

In the thunderfunk webpage this picture was posted as the gutshot of a rocket but seems to be a Liverpool build.

See the mix of diferent pots, second shielded wire from pin 2 V1 to volume pot, also there a grid resistor same pin 2 and the shield seems to be connected to the plate pin1, that one in Gerald Weber's book is a trick to stop oscillations and so is the grid resistor. Check also 100k plate resistor has a ceramic cap across, that one seems to be other little band aid and so the other cap in parallel to the 0.0022mf pvc cap, there's a ceramic maybe same value, reminds trudy.

It seems that Ken or whoever put this together had a very temperamental build and tried to stop oscillations everywhere....

That amp was built by Dave Funk and tuned by KF for a guy that used high output super distortion humbucking pickups. They had to "dumb" the amp down to work for the guy.

[Cliff Schecht]

So the short of it is, to tune the oscillation outside of the range of normal play?

Regards,

Rev D.

Not what I was getting at. The point isn't to shift the resonant frequency as much as it is to simply assure that there is just enough dampening happening to keep the amp from feeding back with a grounded input and your typical knob settings (i.e. maxing out the knobs is just asking for oscillations even on Ken's Express builds). This is just what I've found in practice and may not necessarily be what Ken was doing too. My usual settings on the amp with my Tele tend to be very conservative though to prevent from cutting peoples heads off. Especially treble, it stays on 2 to 3 usually but sounds perfect in that range IMO.

[RevD]

Gotcha. I would imagine with the Tele especially that treble would be turned back. I know the 75 Tele I have with maple neck is obviously rather a bright guitar. I like bright, but not like Albert Collins bright although I dug his tone, just not for me. I know with my amps I turn the treble back as well. On my humbucker guitars, I open it up a bit more as they're darker.

Regards,

D.

[Noel Grassy]

This is good stuff!

NG.

[redshark]

Yes is always good to read all the experiences from people that attempt to build an express.
This build is known to be very finicky and I always though that the "everything matters" statement was an exageration but it's not.
The amp is so on the edge that the position of each wire, the lenght, and the type of components used, even the solder on the joints can make an impact in the overall performance.
I wish all the owners of the original express amps were at least willing to make youtube demos like Glen to see how the diferent amps performed. Then we could have a better point of reference when voicing our clones.

[Noel Grassy]

^+1! Wouldn't that be a treat? I suspect we might not enjoy the spirited
playing as much as we do Glen's.

NG.

[RevD]

Perhaps post a challenge, the Oscillation test... Have everyone that will run a series of test (i.e. Treble dimed and volume up with guitar connected, no guitar connected etc). Just to see how the clones fair, maybe many might not have thought to even try those things to induce oscillation? Just an idea.

Regards,

D.

[paulster]

Perhaps post a challenge, the Oscillation test... Have everyone that will run a series of test (i.e. Treble dimed and volume up with guitar connected, no guitar connected etc). Just to see how the clones fair, maybe many might not have thought to even try those things to induce oscillation? Just an idea.

A good test is to set all the controls to 12 o'clock, bright switch on (either position) and then dime the treble. These settings can reveal oscillations that won't occur with the volume or other controls dimed so can very easily go unnoticed since this isn't a typical control setting.

Mind your ears when you do this though, because if your amp is susceptible to oscillation, you'll basically get a full power blast of hum once you get the treble in the right spot.

[redshark]

Paulster with the exact settings that you mentioned I can't get my amp to oscillate, it only does when having the treble dimed I also turn volume up, then maybe get a mosquito like oscillation around 3pm and get a squeal almost at full blast....So did my amp pass the test?

[JamesHealey]

my express never oscillates even with every dial on full and every setting between.

wasn't hard to achieve this either.. maybe it's the layout I chose it's not exactly KF.

[Richie]

When testing preamp tubes, i have everything full up, then go through tubes till i get the ones that will hang in there with no problems. Then start to pic the ones that also sound good of those i found to work. Also V1 and V2 work in a combination. Find the best tube you can, then put that in V2.
Before even trying to find one for V1. And going through tubes, i don't mean 3 or 4.. unless you get lucky at the start.
Its always best to try and pre screen and find tubes before hand, that you know will work. mark them and set them aside.

Also, it might be noted that, the tubes have different gains to them, well they are supposed to be by the spec sheet data the same.

But, if its your amp, and you know your not going to play the amp full out on all the controls, you might find some that may not squeal in the test,turn out to have less gain, and thats why they are not squealing.

So that is one thing to think about. If you use the tube that doesn't make the amp squeal, then it may not go into feedback as soon as another higher gain tube.

Just trying to get at, if its your amp, and you know how you play it, you might find alot more tubes that work with you amp, at your normal setting, to slightly above.
I found some really nice RFT, and BugleBoy, early EI.and M8137 sounded great. There are many others too, but those really stood out in the amps.

Also remember, somtimes using a tube shield, will remove the high squeal when presence is cranked. Other times it might be the opposite.
And usually the amp may sound just a hair thicker with the shield off, that sometimes depends on the tube. Be sure the output jacks are grounded.

[redshark]

The question here is......

How do you know if the amp's high pitch squeal when volume and treble are dimed comes from the tubes or from an oscillation problem caused by lead dress?

Sorry if this is a dumb question but unlike other people here I'm not an expert and I didn't have an electronics formal training.

[funkmeblue]

tube swapping, see if the problem changes or stays the same

[redshark]

I haven't tested for high pitch squeal yet but I got a good "tube tweak" on my express. I was running a tungsram in V3 and two Ei's in V1 and V2.
Today I got an old telefunken ribbed plate (long) ECC83 with nice matched sections and put that one on V3 and moved the tungsram to V1. I feel that the lower gain longer plates in V3 was a good tweak since it increased the headroom a tad and the tungsram in V1 is richer in harmonics than the Ei so it gives the amp a more 3D sound. The Ei that I had in V1 was moved to V2 after comparing to the original Ei in V2.
This amp has to be the most "tube sensitive" amp that I've ever heard.
I will enjoy the tone for a while and don't want to run any acid test at least for 3 days LOL but I will definitely do it. I need to make sure Daniela doesn't squeal anymore....but I kinda dig this tone....

[Structo]

Trainwreck Express!

Not for the timid!