Inspiration for amp project wanted

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Tubetec

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Nov 18, 2015
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Ive just scrapped a little peavey vypyr with a funky dsp chip ,and Im left with a fine cabinet/speaker and chassis.
I have a set of transformers given to me years ago by the boss of the studio I used work in ,it was a kit of some sort I believe.
The mains tx is quite large for the original 2xEL84's and ecc83 based setup ,so I reckon I could possibly get away with 6v6's instead .

Im just wondering if the other amp-heads in here have any particular favourites in the 15-20 watt tube amp range,
the output transformer seems to be ultralinear tapped. I was thinking of having a series of switchable coupling caps at the input to the first grid as a bass cut filter, I know that wont give a steep cut-off but thats ok too  ,maybe simple treble and mid controls between first and second(phase invertor) , just old fashioned clean to drive non master volume would be perfect. It'll be a tag strip point to point build .

Nothing is set in stone at this stage and Im open to all suggestions even slightly off the wall ones .
Thanks once again.
 
Maybe build something with an extra output transformer split off between the preamp stage and final amplifier, so it can double as a DI.  Make the front panel out of plexiglass and paint the PCB and/or other non-tube components with different colors of florescent paint.  Then take a tap off the 12V filament supply to power a small ultraviolet light inside the cabinet.

At least it'll LOOK cool!  8)
 
Nice one Curtz,
I have used perspex before for a front panel ,and finished it with multicoloured transfer stickers for the labels ,looked very psycadelic. The di idea can work too ,but carefull screening is required from mains hum ,I might try  centre tapped to ground resistors  on the speaker line and an attenuation network to feed a balanced line level signal to an xlr out .
Come to think of it a small tube reverb driver stage ,could easily double up as a di out too ,Another idea ive had sucess with before is a NFB cut/boost ,footswitchable , you set your output to soft clip with feedback engaged ,dissengage 10db or so of feedback and your into full on scream territory .
Thanks for the suggestions . 
 
I have built a few in this wattage range. I suspect you have considered the AC15 and Marshall 18W (model 1973/4)? Both are 2 x EL84. You can obviously build an AC15 with a 12AX7 or EF86 V1 (or both). I built an AC15 with three different lead channels: EF86, normal and top boost. On the normal channel I inserted a capacitor switch (V1 coupling cap) and starting from 500pf (standard AC30 value) went up to about 22n doubling the capacitance at each switch point. Matchless does something similar in their Nighthawk (which shows similarities to the AC15 EF86 version). You could look at the Supro 1624t which has either 2 x 6V6 or 2 x 6973. There is a whole world of other American amps  (e.g. Valco, Gretch, Gibson) that I know nothing about. A lot of the amps I have mentioned have tremolo (which you can easily leave out to streamline your build). I would vote for the Marshall 18W tremolo, at least it is the one I use the most. Almost forgot to mention the other obvious 2 x 6V6, that is the Fender 5E3. I probably prefer my 18W Marshall but a friend of mine said he would take the 5E3 any day over all of the above options. Comes down to taste.
 
What do you want to do with it? Will you use it or sell it? You could build a harp amp,  optimize the design for harmonica. I don't know what kind of market there is for something like that. I'm not much of a salesman, but I do build amps and I have sold a few that were built for specific uses.  That cab has a 12" speaker? plenty of room to add a reverb tank. I like a pre and master volume, and I prefer a tone section like Ampeg where the treble and bass seem independent from each other, unlike Fender tone controls that seem interactive. Do use the ultralinear taps. Maybe line up a buyer and work with them to build something custom.
 
Trainwreck style is relatively simple,  but that's what makes it so good.  You can tweak things to your liking,  each component change is magnified.
 
I always thought (perhaps incorrectly) that good / classic amps were designed in reverse (starting with the output and working backward) so that the limit of each component is pushed such that, when cranked, all of the components are evenly and slightly overdriven. If you just peice together something without carefully checking the threshold of each component, the most likely outcome will be that only one component will limit the signal and the rest of the components are not being heard. A progressive stepped clipping, saturation, sag is going to sound louder without being just a buzz saw.

Just thinkin' out loud though.
 
Thanks Squeaky and Walter ,

I have right next to me a '74 JMP 20watt ,its actually the PA version ,but I added bleed caps so its the same as the lead version ,great little amp alright , I made a slight change to the phase invertor on it too ,and upped the value of cathode bias resistor a small bit ,just gives it a bit more dynamic punch . Im very tempted by the Ac15 and the 5E3 as well , I have a couple of other EL84 based units as well , Something with 6V6's might be a nice addition to the collection ,just for the tone difference they give.

Ive tried a switched coupling cap bass cut system before on a cathode follower tube mic actually ,Im really fond of it ,even though the slope is very gentle ,with 12 positions a sweet spot is easily found , Ive had great results as a drum overhead .

The cab as it stands holds an 8 inch ,but it definately looks like a 12 would fit in if nessesary and space for a tank too .
Ive plenty of guitarist friends ,but very often I become sentimentally attached to my builds and cant let them go afterwards  :-[

Ive got all the gear I need to set up a small but high quality studio ,this year fingers crossed ,Ill clear my garage of junk ,add an extra wooden shack on the side ,and be able to make some coin doing recording projects .

The Ampeg is another one that interests me ,often they have a Baxandall tone section ,which Im sure is what your refering to Walter, Ive never tried it in a guitar amp ,but I do have a stand alone tone shaper for recording purposes using a special Siemens C3G tube , its so simple ,yet its gives upto 20db cut or boost on high and low bands , it'll also drive 70 volts into medium or high impedence without breaking a sweat , Ive maxed the plate current and voltage and gone with a big 10k ohm anode load resistor ,only downside is input impedence varies to some degree depending on the amount of boost or cut you dial in .

Even though I have a guitar ,Im not much of a player ,and I not just being modest about it ,think like a roadie doing a sound check ,thats what i sound like  ;D .

Anyway thank you kindly again ,definately food for thought there , I'll throw up a few pics as this build progresses .
 
Hi John and Squarewave,
Yeah the trainwreck Im familiar with ,Ive seen the schems of one or two of them ,sorta AC30 style ,never worked on one yet though ,I do have a couple of JMI 60's vintage AC 30 chassis with good transformers on them alright ,but they would require a total rebuild at this stage ,I'll get around to it at some point alright though .

Theres definately truth to what your saying Squares ,as your signal gets amplified you want extra headroom in the later stages to handle that and create a smooth transition from clean to distortion , of course if you want  full on Boogie style cream ,you end up needing attenuation between stages too .

I'll probably do a bit of a pick and mix on this build ,make something a bit unique with building blocks from well tried topologies .
I'm  all full of enthusiasm now , I might even start sizing things up on this chassis tomorrow.
 
The Dr Z.  Karmen Ghia is interesting to me right now.  Its called the Phoenix  on AmpGarage.  There is a layout and Schematic.  I have if you need.  Check out a you tube video of Dean Parks  playing that thing.  Great player sounding really good with that amp.
El84s with a unique tone control.  Old Selmer amps had a similar tone circuit.  Very simple and great sounding in right hands.

https://www.youtube.com/watch?v=BPCL0HVtoxk


I have 2 donor chassis.  A Standel with EL84s and a Thomas organ tube amp that uses 6973's.  Its actual a 2 ch amp with a Main amp and a Leslie amp.  I have the Leslie and cables out of the organ so it works as is.  Weird phase splitter and feed back on the Leslie amp but it sounds cool just plugging In.   
 
Very cool Fazer,
I like that combined hi/low tone control ,its just one of those ones where you instinctively know the sweet spot when you hit it, simple, intuitive,brilliant.

I love repurposing/modding old stuff too ,everything from dansette record players, reel to reels and old radio grams,they dont deserve to go to landfill  ,some new caps, psu and coupling, a few tweaks and you have something ready to give another lifetimes service  ,and the spirit of the hands that made them lives on inside too. This disposable society we have now doesnt sit well with me at all .I'll check out Dr Z's tomorrow , but yeah do post the schem and layout if you like .
Thanks again.
 
Good luck with your project Tubetec.

I've owned a '64 AC30 for nearly 30 years now, normal version. The original speakers were long gone and the cabinet was pretty beaten up (I've sometimes thought about what that amp has been through). I proceeded to blow it up a few times extracting various noises out if it in attempts to make music. I bought it for not much just before grunge music made such amps popular again. Too loud for me now (I've pretty bad tinnitus from tracking solos in headphones at unholy loud levels) but I don't think I'll ever part with it.

I've been toying with the idea of building a low wattage franken=amp for a while now. Kind of British up front and American (mostly) at the back (6k6s maybe). One day I'll have all the parts a hand and give it a go. I bought a huge Russian 20uF oil cap (can't remember why) that I'm going to use for V1 cathode bypass. Maybe some non-standard plate resistor values (harmonic consequences?). Once I settle on the tone control it might spur me on a bit.

I like to work on the principle that a guitar amp doesn't have to do everything, as long as it does something really well.
 
I love repurposing/modding old stuff too

I feel the same way.  It might be I'm just cheap but a throw away society is just wrong.  We have to have LED light bulbs or florescent bulbs in this country.  But how much mercury do we throw in the trash overtime, they go bad. Just double talk to sell product.  Tubes are cool sonically for guitars and other things.  I'm gonna use what tickles my ears while I can and already own to many amps  so repurposing amps are how I do it these days.  Keeps me off the streets.  As long as I have some 90 shilling in the fridge and friends over on weekends to jam, I'll do fine. 
 
fazer said:
We have to have LED light bulbs or florescent bulbs in this country.  But how much mercury do we throw in the trash overtime, they go bad. Just double talk to sell product.
Not sure what point you're trying to make but the amount of mercury that reaches a landfill because of improper disposal of florescent bulbs is significantly less than what would have been emitted by burning the coal necessary to power the equivalent less efficient incandescent bulb. So they're so much more efficient it's a net win.
 
Point is we throw appliances away after a few years of use.  Old washing machines lasted 20 plus years but new ones need fixed every few years .  A control board sealed in epoxy is completely replaced rather than repaired.  Electronic assemblies are easy to toss rather than repair.  It’s a different age and I grew up n an old one.  Tube amp chassis are easy to repurpose.  Today’s electronics are usually throw away.  The LED porch light lasted 2 years not 10 year as shown on the package.  Never mind. I know cars last longer than in the past.  This is best left for the brewery.  Not a post on a great subject to me,  tube guitar amps.

It’s just a rant squarewave.  I’m being dragged into the future no matter what I think.
 
Thats a nice neat setup on the Dr Z alright , nice quality components as well .

Im not sure how all these so called eco friendly things will pan out either ,sure it saves us in energy here ,but what about the people who makes flourescent and led bulbs ,I'll bet its a pretty dirty industry in itself . Leds contain something very dangerous indeed ,Gallium Arsenide . Very few people realise if a flourescent light bulb breaks in your house your supposed to open windows and doors immediately to let the mercury vapour escape .Of course these types of bulbs arent supposed to be binned with regular waste either ,but they still end up there . Poncing off the dirty work on poor people away someplace else doesnt count as eco friendly in my book .The computer industry is one of mans most wastefull endevours ever ,and the really bad part is guns ,war and regime change are often required to get the resources at a good price in the first place .Maybe a better topic for brewery alright.
 
Yeah, this is definitely a conversation for The Brewery.

But I have to say one final thing which is that we don't know the math. Yes, there are many things that are bad for the environment and its inhabitants. But there are matters of scale that have to be considered. I think that is where even people with great intentions go wrong.
 
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