The edge of instability......

[redshark]

Well, I think is well known here that the Express and Liverpool are designs that are always in that line.
Reading an old thread "approach to harmonics" Ken commented that all his amps were born squealing and screaming and that using diferent techniques he got them stable without bandaids....Well

I think I found some of those.....

Check pics of Francesca,
Then check pics of undocumented express....
then....check the Trudy schematic......
Then see the Liverpool gutshot that is in the Thunderfunk website that claims to be a rocket.....

Then finaly read "tube guitar amplifier essentials" by Gerald Weber...book written after the trainwreck climax incident....
Chapter..."taming the parasitic beast".....

Read between the lines...connect with pics.....

Maybe that will help......

[redshark]

For reference.....

https://tubeamparchive.com/viewtopic.php?t=21

[Structo]

Thanks for reminding me about that thread. I read it quite a while ago but it was good to read it again.
Ken was one of the good guys for sure.

[Jana]

I saw the thread title and thought it was a page from my therapist's notebook.

[jaysg]

hmm...my liverpool is quite stable with any preamp tubes...did I do something wrong?

[redshark]

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....

[redshark]

Anybody knows if that is a "real" liverpool?

[rooster]

redshark - OK, IMO, I have to say that this is a real odd duck. Translation: fake. There's just too much that looks hacked together for it to be built by KF.

I would bet that somebody here knows who built it but I bet they would never talk about it.

And this is not to say that I am someone who has directly been inside a real deal TW because I haven't. But Allyn, Richie and Glen have. I would be curious about their opinion.

[geetarpicker]

Seems the Thunderfunk site mentions he built some wrecks for Ken, and if we believe that perhaps this is one of them. Appears to be a Liverpool. Bud chassis, one wire wrap pot, correct looking signal wire & shielded cable, etc, but lot's of "fixes" it appears. I personally had not heard of anyone helping Ken build amps back in the day, so the Thunderfunk info was news to me a few years back when I first read about it. Personally I don't think it's a "fake" but perhaps just like mentioned a wreck built by Thunderfunk with perhaps at least some parts from either Ken's stash or original sources of such.

[funkmeblue]

seems interesting to me that anything not in francesca is a "fix". Could it just be that he was voicing this particular amp for a customer? The resistor and cap on the second stage was also in ginger. Anyone know what value of adjustable resistor and cap value?

[Jackie Treehorn]

My "interpretation" of what Ken was getting at in that paraphrased conversation is that you need to strike the mean between stability and wide bandwidth, at least in the preamp. I think what people are calling fixes and band aids is what I call "fine tuning!". That's where the magic happens!

I don't know how Ken chose to tune, but whatever he did I'm sure it was either, gain reduction, attenuation, or eq in some combination.

There's too much importance placed on the Francesca photos. They're useful in many ways, but they don't tell the whole story, just the last chapter. Nonetheless, I think things like the parallel grid and plate wires on the second stage might qualify as a band aid, it just escapes criticsm since it's local nfb without any extra parts!

Way back in those heady pre-Francesca days, I was trying to get more harmonic feedback and even experimented with positive feedback since I read some Ken quote about his amps being part oscillator! It was certainly the wrong approach, though, because it's stability that brings out the feedback, harmonics, and sustain. I don't hear anything positive from instability. In fact, once the amp is stable, a lot of problems like brightness and noise are greatly reduced.

[redshark]

Well, I have a few comments and I hope this doesn't upset anyone....

I find that the "urban legend" side remains pretty much nowadays in the trainwreck forums.

This morning I had a conversation with a friend of mine that went to the NY amp show this last weekend and he went to the celestion room and played Suzanne, express owned by George Lynch at some point and now by Ultrasound. His comment was that the amp sounds incredible although it seem a little bit too bright for him with high treble switch and that his favorite setting was in the "mild" switch with eq at 12 noon, presence on 10-11 and volume at 1pm. the cabinet was a 4x12 with I think G12H30's, maybe that is where the "brightness" came from. Anyway at some point once he unplugged the cable from the amp he turned the treble like at 3 and started diming the volume and guess what? the high squeal came out.
That high squeal that has been torturing me since january and that made me feel my amp wasn't right.
My amp, just like Suzanne sounds very good with a cable plugged in and "normal" settings. Even if I dime it(volume) as long as treble and presence are not dimed the amp don't oscillate.

So I've been chasing this tail for months perfecting my lead dress, paying high $$ for prescreened tubes, and doing a couple fixes which cut the oscillation problem almost to a very extreme setting just to know that a real one oscillates just like mine.

Jackie, now I believe the oscillator comment said by Ken....

Well, at least I will be able to sleep peacefully tonight.....

I have to say that while chasing this tail something good came out of it which is getting better bloom. My amp sounded a little bit congested before but now it blooms like a champ....

I'm gonna quote Forrest Gump....."and that's all I have to say about that"....

[Cliff Schecht]

Something I mentioned before that I noticed with my second Express build was that the amplifier will build into oscillations very slowly with "typical" guitar settings and a grounded input (I used a grounding input jack). Whenever I would put my finger, even lightly, on the open area by V1, the oscillations would mostly dampen out, even with volume cranked through a 4x12 and an open bottom chassis. Using a chopstick or other nonconductive material would dampen this natural resonance as well, eliminating the thought I originally had that natural human capacitance was somehow helping to dampen the amp a bit. I'll bet that every Express build has it's own natural frequency at which it will oscillate when built properly, and tuning/mucking with this natural resonance is how Ken tweaked each amp to his liking. I think this is why Ken used the strips of weatherstripping in his amps, it served to help dampen the chassis a bit and reduce the tendency to self oscillate while idling while still allowing the thing to sing when signal is present.

[RevD]

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

Regards,

Rev D.

[geetarpicker]

Even if the oscillations are out of the range of hearing they still may distort the amplifier stages and in turn cause ugly modulation of the audible range. It will sound somewhat like the ghosting you get when you crank some amps, but it will even be there when you play quietly. Point is with the oscillations you are typically clipping the amp, even before you hit a note. Ugly stuff.