Output tube impedance

[Chuck H]

Well, keep it in the back of your mind so your ears pick up anything in the woods. But I honestly think that Ken simply listened to the amps and decided that a little high was better sounding. So when he ordered the Heyboers he stayed high, though not quite as high as the Stancor. He likely paid more attention to other aspects of the design. Ken could occasionally surprise with some tech. He was careful not to speak out of his depth, but generally came across as a well seasoned, but not technically educated amp guy. I know he had an actual job related to amps with a famous maker before he did his own thing. But IIRC he was just an electronics enthusiast when he took that job and his skill at repairs moved him up the ladder. So he was good, yes. But hardly an engineer. My point is just that I don't think Ken ever made any finite decision about specific harmonic structures and OT primary impedance. He was more likely to notice the tonal difference between impedances in general and consider it in his designs. Not nearly as finite as people would think. He also did things like move OT's around, holding them in his hand while the amp operated so that he could choose the quietest place. He also experimented with component location inside the chassis because it actually can make a difference. But I strongly doubt he was ever the genius that could look at a hand wired board and tell you what would happen if you reoriented "that capacitor" 180*. Through experience (building ham systems) he may have had more odd clues about layout anomalies than most hobbyists, but the stuff engineers know about transformer design was probably not his to own. If people would stop idolizing him and try harder to get into his real head/perspective they might have an easier time unlocking his secrets.

[Leo_Gnardo]

Why would someone choose a non ideal OT primary impedance AND what would be their criteria? I don't know and it probably doesn't matter as much as some people might think it does. At least Ken didn't think so.

When scratch-building, most folks use off the shelf OT's, and few of those have primary impedances that are an exact match to the tube-guide charts. Besides, who knows how close today's tubes - or NOS for that matter - are to their claimed specs. We have to deal with what's available. More advanced builders could special order iron from outfits like Heyboer or maybe Edcor. Another piece of Trainwreck lore that fell into my ear (OW!) for some of them Ken used OT's he pried from Dynaco MkIII power amps, intended to be driven by KT88. Maybe he liked the tone? Could have something to do with it?

IF there's an answer, Ken took it with him. Another bit of 'Wreck lore, which you may believe or not as you wish: Ken tweaked each amp for its intended owner, so you'll doubtless find variations in each model type. If he was around today he'd probably advise: what's the point in beating your brains out trying to ape the 'Wreck? (And which one???) What's important is that you build an amp that suits what you're looking for, your ears, your speakers, your guitars. The Express is a good format for builders, it's not awfully difficult to make one if you're so inclined. Then set to work dialing it in for yourself. That would be a proper continuation of the Ken Fisher legacy.

BTW I caught the Colonia reference early on. I grew up about an hour's drive north, and my Aunt Betty lived right down the road a hop & a skip in Old Bridge / East Brunswick. In spite of all that I never got to meet the guy, though I have met some of his amps and their owners.

[Enzo]

So why would a designer deliberately choose a primary impedance that is not a dead match for the output tubes?

because there is no "dead match" for the tubes. All this happens in a spectrum. There is a wide range of values that are perfectly fine for the circuit. The output impedance at the load is only a nominal value, if you look at any speaker impedance curve you see a huge range of values with respect to frequency. All those impedances are reflected back to the tubes in equally varying amount.


The designer also has to consider how it sounds. We are not making hifi amps, here, we are making the opposite: amps that do indeed color the sound and distort. If a "wrong" impedance pushes the tube operation down its curves a bit and we like the result, well, it isn't wrong then.

[Fretts]

Thanks for all the views - very enlightening.
Bob Gjika has videos on YouTube about his own amps and his experiences with Ken Fischer come up in conversation. He adds detail to a lot of the snippets of gossipy lore that are always around about Ken and his work. The transformers, the problems, their conversations. It's interesting. I had a postcard correspondence going with Ken for a little while in the 80's and called him on the phone a couple times. I thought he was a fast-talking, fidgety character, albeit very forthcoming and generous with his time, with a strong focus on "purity" - few components, short wires, few features, no frills. I don't know personally, but I would not be surprised if his motorcycles were stripped-down like that, just the pure essence.
I have to apologize to DaBreeze - I seem to have totally highjacked this conversation! Sorry about that. Don't ever start one about Tesla, we'll be here for weeks.

[Chuck H]

Ken tweaked each amp for its intended owner, so you'll doubtless find variations in each model type.

And yet, not so much. It's actually hard to find (or filter for) actual Trainwreck circuits on line now. But once upon a time there were a few chassis shots and some circuit blueprinting going on for a few others and the Express amps are pretty much all the same. The only exceptions I've noted have been a 1.5k grid stop on the second triode in one amp, shielded or unshielded input, where that shield was tied and the slightly different OT's used. In the Liverpool's there were some differences in the load to the third triode with some examples having 68k and some as high as the Express value of 150k. but really, not much deviation to the circuit in the majority of amps. If he was tuning these amps for individual owners he was doing it within the component specs because the marked values are the same. He did talk a lot about selecting the right tubes. So that could be another customer tweak I suppose. But since he's dead and tubes all differ a little, well... Glen Kuykendall has a few videos where he compares his and someone else's Express or his two Express's side by side and talks about the differences, but the differences are so subtle as to be almost ignorable. I imagine it like telling someone how great a bottle of wine is before they try it. 90% will love it immediately based only on what they heard about it with their taste buds fast asleep. Ken even kept his own personal Express that he called "Reality Check" so that he wouldn't get lost in the effort of building a new Express. Age, ear fatigue, how you ate that week, the rain, etc. can all play games on your perception. But the point is that he used the same reference point for each new amp. Smart, but it hardly implies custom for customer. But if you're Ken Fischer you can tell anyone that their amp is special weshial and they'll just swoon and love it.

[Leo_Gnardo]

I imagine it like telling someone how great a bottle of wine is before they try it.

Roger THAT ^^^^^ !!!

Also veddy smaht of Ken to keep a copy to compare his other builds. McIntosh did the same with their hi fi gear, at least in the tube days.

with a strong focus on "purity" - few components, short wires, few features, no frills.

Matches my principle: "Simplicity yields clarity."

And you needn't worry about the OP, he's been missing for 9 years more or less. Lots of hijacking and necrothread revivals around here, that's the way we roll. Kind of a pirates of the Caribbean for guitar and amp guys. I'm gonna have a tot of rum now, shiver me timbers!

[Fretts]

And yet, not so much. It's actually hard to find (or filter for) actual Trainwreck circuits on line now. .......
Ken even kept his own personal Express that he called "Reality Check" so that he wouldn't get lost in the effort of building a new Express. Age, ear fatigue, how you ate that week, the rain, etc. can all play games on your perception. But the point is that he used the same reference point for each new amp. Smart, but it hardly implies custom for customer. But if you're Ken Fischer you can tell anyone that their amp is special weshial and they'll just swoon and love it.

I do have some gut shots of Francesca and of Ingrid from when it was possible just search for them. Chris Merren prototyped transformers for Ken after the Stancors disappeared - 12 revisions he says, Ken was looking for something a bit brighter, says he - and sent the specs to Pacific Transformer to buy 50 at a time. Chris told me the story of how bad those Pacific transformers were. The QC was terrible, most had specs all over the place and they didn't follow the winding sheet. Bob Gjika says that all that hand tweaking wasn't custom-tuning for a customer so much as trying to wrangle an amp with an out-of-spec Pacific transformer back to sounding like the benchmark, the Reality Check Amp. If he couldn't get it after altering three or four parts, the tranny came out and went into a box of duds, and another one was swapped in. John Mark - "JM" - corroborates this. He was a close friend for a long time and in recent years, the Fischer family and JM came to an agreement whereby he would build new Trainwrecks, in their house, on Ken's workbench, to Ken's specs, with their blessing. All Ken's "lab notes" are there and the Reality Check amp is still there for reference. So you could buy a sanctioned "real" Express now if you wanted to - they're $5K.

[Chuck H]

So you could buy a sanctioned "real" Express now if you wanted to - they're $5K.

Which is the only happy ending to any of this. Provided the orders are there and the people who need the income are ok. Ken worked hard when he could with what he had and died undiagnosed. He actually couldn't work much for more than a decade prior and if the family can use what he built to generate an income and provide a wanted product to some happy buyers then everybody wins. If you're hankerin' for an Express then there's no better way I can imagine to get one than from one of Kens actual confidants that is working with his notes, on his bench and comparing to his existing benchmark. It's not built by Ken, but you can't possibly get closer and you can get it for 20% or less than you'd pay for an original. Not to mention that since there are only 100-"ish" original Trainwreck amps of any make, model, prototype or custom incarnation, continuing manufacture of the line with some sense of integrity to the original intent satisfies a demand and perpetuates the only classic amp ever made in such low numbers. Sort of like the amp version of saving an endangered species and setting a family table at the same time

[Pedro Vecino]

I do not know that amplifier. I imagine that if they are so exclusive, few people will have had them.
Can someone put a video of the most representative example of that amplifier to understand what is being pursued?
Thanks!

[Chuck H]

There are a couple of session players that used them on many commercials for TV and radio, but it's obscure finding out exactly which ones. There are also rumors about a couple of bands whose guitar players used them on this or that track. Some denied by guitarists though. I've read there one parked in a famous Nashville studio, so who knows how many tracks and from whom it may be on. These amps have propagated behind the scenes in the industry among those in the know. Probably the best known proponent of these amps is a very good player named Glen Kuykendall and he has several clips on *outube that are easy to find. There are also a great many clones and straight up copies on *outube. So if you want to hear the real deal, not a clone or copy, stick with Glen's videos.

This is a clip I always liked because it's NOT a PAF guitar or a strat like all the other TW clips. It's P-90's and it really shows of the amps particular character. Sort of crunchy but saturated with nice swirl and bloom.

http://www.kometamps.com/user/uploads/60_09.mp3

[J M Fahey]

That ^^^^^
To see what it means electronically, hereīs one of the back engineered circuits.
Which differ all over the place, in great part because the *originals* were all over the place too:
http://www.blueguitar.org/new/schem/...k/wreckxpr.pdf

it starts with (why am I not surprised?) .... "a Fender"
Basically same preamp and power amp

To which 6 tweaks are added

1) an extra tube gain stage (so far, what Randall Smith started with, 40 years ago, with Mesa Boogie Mark 1 , go figure), so of course it has much more sustain and grind than, say, a Twin or Super Reverb on 10.

2) BUT, itīs not a plain "Fender" gain stage (which would make it same as the example mentioned above) , instead itīs the very particular sounding "Marshall cold biased" gain/clipper stage of JCM800 fame (and most High Gain amps following it, from Soldano to MBDR to ....) so it has a more grinding, buzzier and biting sound than any Fender, yet it does not fully cross into Marshall territory.

3) to make it cleaner, even when clipping, he added a highpass/low cut á la VOX, which makes for a janglier sound.
2000pF into 150k is quite close to VOX 500pF into 470k .

A plain gain boosted Fender might be farty, because they have lots of Bass; cutting them sharply improves sound while keeping gain high at mid/high frequencies which improves harmonics big way.

So in a way, for me itīs a "Fender meets Marshall meets VOX" combination, which happens to be very tasty.

I was almost forgetting a *very* important point: it has NO repeat NO master Volume of any kind (not even PPIMV) so what you hear is either very clean jangly sound or pure creamy power tube distortion, with some added bite added by the cold clipper stage, enough to make it interesting.

4) he replaced Fender NFB with a Tweed/Marshall type, including Presence.

5) tone controls are "halfway" between Blackface and Tweed/Marshall, just check values, play with them in TSC and compare to Classic ones.
In general it has slightly more mids and less range than classic Fender (Treble is shifted lower, Bass is shifted higher, so Mid dip is shallower) which is not bad at all.

6) there is an undocumented tweak which is NOT in the schematic (might be in the layout though, pity thereīs none "officially approved" available)

If you listen to YT videos or MP3s youīll notice there is a very bright ring present, very tasty ... which is not reflected in what the schematic shows.
No bright cap in the volume control, no small value caps in parallel with cathode resistors ... yet that brightness is there.

Myth says that Designer had put certain wires in close contact which should beter kept well away, under penalty of uncontrolled oscillation.

Now oscillations happen at certain frequencies, usually very low (motorboating) of which there is no chance here, because of strong low cut, *or* at quite high frequencies , basically because the small parasite capacitances coupling "what you do not want to couple" let high and very high frequencies through easier than lower ones.

Now when you separate wires to correct that, there is one point when continuous oscillation is stopped, but there is still some "ring" at that frequency ... which if within the audio band will sound like a narrow but strong boost at a certain frequency, think a single band in a Graphic Equalizer or what you can achieve with a Parametric filter.

Myth says that Designer moved wires here and there until he got the right sound

Of course, there is no way to show that in the schematic, and I guess is part of the Mystery surrounding this amplifier and makes it hard to clone exactly.

Where is that "ring"? ... 2 kHz? ... 3 kHz? .... higher?
All I know is itīs very distinctive.

Maybe the old shop hand mentioned above, who has built them before and apparently has all of Kenīs Lab notes can reproduce them the right way.

I think Ceriatone also cloned these (like so many others) but I fear they are missing this important point.

[Chuck H]

Continued discussion of other aspects of the circuit could probably be directed to another existing thread, but hey, NBD really. So... The TW does look in some ways like a kludge of ideas from existing amps. The Fender BF topography, the added gain stage (Boogie), the 10k cathode clipper (Marshall) and the HP filter close to VOX frequencies. But you can say this or that amp is like this or that amp pretty much across the board. And we all know that you can't just piecemeal circuits from different amps together and expect performance. In the end I think it's just the circuit he ended up with. One unique feature Juan didn't mention was the .1uf coupling cap to the PI. Since the PI is doing most of the duty cycle shift (swirl and bloom) this cap value is important to the effect because it charges and discharges slowly (time constant) by comparison the the typically lower values used here. I've experimented with this and watched it on a scope and the results are very interesting. I did try it out on a model I build that's sort of like a Trainwreck design. I didn't like it (for that amp). It compressed the attack in a way that felt strange to me. But in the Express design I think it's a major part of the amps tonal character.

[Leo_Gnardo]

I think Ceriatone also cloned these (like so many others) but I fear they are missing this important point.

Good analysis Juan! I got to work on one of those Ceria "clones", hmmm, maybe 12 years ago? It was actually pretty darn good, except the guy who bought it had only one complaint, that it rang like a bell! A very small bell at that, "pinggggg..." Turned out to be a stiff wire that ran from the circus board to the grid of the EQ drive tube. I could pluck that wire and generate a "sproing" noise that quickly settled down to a high frequency whistle, maybe 4-5 KHz or so, then settled down. Simply replaced the wire with one that wasn't so stiff, with soft plastic insulation. Still had plenty of zing, but no more "ping" accompanying every note. Goes to show, not only wire dress, but selection of just one wire's stiffness / insulation physical qualities can make the difference between unacceptable and terrific.

[Chuck H]

Hmmmm..? Does make me think about Ken reportedly discussing wire selection. That's one that was harder for me to buy into before now. Since he used predominantly NOS preamp tubes and at high gain levels most go "PING" if you tap them you actually ARE influencing the tone of the amp via tube microphonics and physical vibration (feedback). Golden ears? I'm starting to believe it. Of course that means mine are more like, I dunno, aluminum maybe?

[Fretts]

There was a book I once had about "lateral thinking" or something like that regarding creativity in business. There's a story of a guy in the 70's who made an uncopyable amplifying module that had a gain of 12,000 or something crazy like that that was theoretically impossible given the parts being used. Turns out that in order to make it super compact, he took what would have been a long, narrow circuit board, halved it and folded one on top of the other, parts facing each other. Then some final trim tweak was performed until it "went into mode" (quote from the book) and then it was potted in a small enclosure. Reverse engineers that cut open examples and managed to identify the parts never got more than a gain of 400 or so, they could not figure out what he was doing. The original designer eventually divulged decades later, when the whole thing was obsolete, the secret - there was positive coupling of some kind that serendipitously occurred when the two circuit halves were placed too close together like that. It was an unintended bonus. He harnessed it and made it controllable and had great success with it that was never duplicated by the competition.
So anyway, it's not unprecedented for somebody with a quick and open mind to believe it when they see it, and then go ahead and run with it.