First Build Ideas

[jjackson7]

So after taking circuit analysis and electricity and magnetism last semester at school I really want to get down to building. Those courses do not at all give me the experience to do this but I feel like I at least have the background to accept guidance without embarrassing myself too much. I have thought about doing some of the projects on this site, but I play in loud bands (one with two drummers) and I normally need 100 watts to have the headroom necessary to cover. My idea is to build a 100 watt amp with two inputs one voiced like a JCM 800 for high gain work and another that could get a little closer to a twin clean (though I don't want on board verb/trem). I realize the preamp is not the only thing determining the difference in these tones but if I could approximate either and tweak from there that would be great. I also have a list of ideas that I would like to incorporate:

-DC heaters
-NFB switch
-EL34 to 6L6 switch (seen this on an Ampeg VL1002)
-tube rect. with the option of using the octal solid state rect. on this site.
-choke

I would like the controls to be as follows: "fender" input, bright switch, volume, "marshall" input, volume, gain, presence, and then common to both bass, mid, treble.

I was going to start by looking at schems of the 2203, AB 763, and the Ampeg (to try to understand the power tube switch).

So at this point I am basically looking for general guidance from people who have "been there done that" building amps and could hopefully keep me from making too many mistakes. I am learning AutoCAD right now so I would like to get the layout done on that for review before I build. I also have access to PSPICE to check the circuit before I build, though I haven't used it yet and not sure if it will help much. I have tried getting some help from school but the EE school cares not for vacuum tube amplification and hasn't given much advice for me ( I'm actually a ME student but guitar playing has gotten me interested in this).

If you've gotten this far thanks for reading and I appreciate any and all advice, even if that advice is to learn more before I start.

Thanks,
Jordan.

[nateflanigan]

Hi, and welcome.  Building a 100w amp isn't really any more difficult than building a lower powered amp but it is more expensive and in that sense not a great learning platform.  What's hard about successfully building a tube amp is more physical than conceptual, you could say it's in the hands rather than the head.  There's a craft to the fabrication techniques that takes a little practice.  Also, it's likely that you'll make mistakes on your first build and if it's a well know circuit that many people here have done it will be much easier for them to help diagnose problems.  So I'd recommend starting with a champ or something, you'll use it, maybe at home maybe for recording, it won't be a waste of time and money.


Regarding some of your finer points...

-DC heaters

Why?  Neither of the amps you mentioned use them.  If you really want to, this isn't a big deal, I just don't think you'd notice much difference.

-NFB switch

I have this on my deluxe, I like it, I don't use it a lot but it's easy to add and can be cool at times.

-EL34 to 6L6 switch (seen this on an Ampeg VL1002)

I don't think this needs to be a switch, you can just try the amp with both (you'll have to make a bias adjustment) and see which you prefer.  I forget the finer points of what connections need to be made to make 6L6's and el34's swappable but it's not a big deal.  Check out the FAQ at london power (TUT book series) he has some interesting stuff to say about output sections.  I think there's some info on this site as well.

-tube rect. with the option of using the octal solid state rect. on this site.

Also not a big deal, if you wire up an octal socket you can stick a pretty wide range of rectifiers in it.  

-choke

I think most high powered amps use chokes, maybe some early Tweed stuff doesn't.  I've never tried not using one.  

There's a bajillion cool things you can do with amp building but's it's easy to get lost in the details, my advice would be to start at the beginning.  If you could clone yourself and have Jordan A build a simpler amp and then the killer sweet dream amp and simultaneously have Jordan B start right in on the killer sweet dream amp I would wager that Jordan A would finish first.

[jjackson7]

I understand the point of starting small. I will go ahead and get a small amp build going. I really have too many amps now so I will clean house a little and then maybe the champ build will be my go to home amp.

As far as DC heaters goes it just makes sense to me after owning a bassman that hummed like crazy. After twisting new heaters and moving wires around a little I minimized it but still noticeable (I'm sure there are other contributors to this but I haven't gone that far with that amp). I have a few modern traynors and though they have a lot of drawbacks and are failure prone they are dead quiet on 10 without a guitar plugged in.

The 6L6-->EL34 deal is just something I want to play with. It seems like a lot of boutique-y tube amps are going the direction of making the power amp section really versatile. This maybe marketing mojo and that is kind of what I want to find out. Switch may not be necessary but could be fun. Again I haven't looked into the circuit yet to see what this would entail. (edit on early post- looking at the VL1002 schem it was a EL34 6550 switch. That makes more sense but not what I want).

One question about the rectifier and please excuse my ignorance but would I just need one octal socket for a 100watt build? I'm thinking of the mesa dual rect here. And if it is the case that I need two rect tubes would I just plug one solid state rect in its place since it looks like the DC from the mesa rectifiers are tied together?

Thanks for the response.

[Willabe]

As far as DC heaters goes it just makes sense to me after owning a bassman that hummed like crazy. After twisting new heaters and moving wires around a little I minimized it but still noticeable (I'm sure there are other contributors to this but I haven't gone that far with that amp).

It might be how you wired/ran your ground's. Fender, Marshall, Vox, etc. all their (random) grounding plans hummed. This is very important as far as hum/buzz. Look in Doug's library for how he likes to wire his builds, look at some of the schmatics of his builds. Also Merlins site, parts from his books are posted there and the Aiken Amplification site good info on this also.  

You can check to see if the heaters are the (biggest) problem by hooking up a 6v battery that is large enough (lantern) to handle the current draw for a little while. Disconnect the PT heater leads, tape them off so nothing will get shorted out and hook up the 6v battery. See what you find and go from there.

You can use a dc stand off voltage for the heaters instead of pure dcv. Works very well. The 6.3acv floats on 30 to 80 dcv. The guys here seem to favor 30/40dcv's, KOC likes 70/80 dcv. I've got 60/65dcv's on the heaters in 2 of my amps and they work/sound great so far. Both very quite.

 
                        Brad          

[jjackson7]

You're probably right about the grounding in that amp. I'll revisit that next time I have it open.

Never heard of the DC stand off voltage. I ran a google search and a search on this board and didn't find anything. Do you have a link that explains this concept?

[Willabe]

Here's the 2 builds that I'm using it in. Here's Merlins site, lots of good info there. Scroll down to DC elevation.

http://www.freewebs.com/valvewizard/heater.html

Aikens site is down for reconstruction. KOC's TUT book series is a great resource also.

            Brad      
  

[nateflanigan]

As far as DC heaters goes it just makes sense to me after owning a bassman that hummed like crazy. After twisting new heaters and moving wires around a little I minimized it but still noticeable (I'm sure there are other contributors to this but I haven't gone that far with that amp). I have a few modern traynors and though they have a lot of drawbacks and are failure prone they are dead quiet on 10 without a guitar plugged in.

Whenever you get to it take a look at what kind of shape are the filter caps in.

I forget what the deal is with the two rectifiers, looking at the schematic it looks easy to wire up though.  There's lot's of powerful amps that only use one rec (twin reverbs, sunns, majors, etc).  I have one of the ss plugs in a sunn-ish build, it's just an octal socket wired like a typical recto socket.  

I was thinking more about your big build, if you use a twin reverb chassis you'll have lots of real-estate to play around with.  For the sake of argument let's say that all the power sections you're looking at are big, loud, fairly clean, and for the most part interchangeable so you might as well stick with the twin.  Then say you stick with a stock "normal" fender channel, for your gain channel that leaves three tube socket spots and three tubes worth of available current from the PT.  There's LOTS of cool stuff you could do in that space, cascade some stages, maybe a parallel stage like the Tweed Overdrive Special.  Should be awesome.

[jjackson7]

Thanks for the info Willabe. I'll start reading.

I did recap the bassman when I got it. I changed one of the caps from a 40uf to a 20uf (can't remember where I got that idea... weber?). I think its a little too bassy now. I'm not playing that one at the moment so I may play with it while I'm trying to figure this build out.

I think I like the idea of starting with the Twin and keeping the normal channel. I'm gonna start trolling for a project twin. Good idea! There should be enough space to build anything I want in that platform. In that regard if I am going to gut a Twin keeping the trannys and chassis do you think a RI would be fine for that purpose?

[sluckey]

The Twin Reverb chassis would make a good base for a 2 channel 100W amp. But if you are going to gut a TR you should consider this...

A 4x6L6 amp would need two 5AR4 rectifier tubes and two 5AR4s would need 5VAC@4A for heaters. The TR uses a solid state rectifier and there's not a lot of room for rectifier tubes. And the PT has no 5VAC winding so you would need to buy a separate 5VAC transformer that can supply filament current for two rectifier tubes. And the TRRI PT requires a bridge rectifier, so tube rectifier is out unless you get tricky.

So, you may want to rethink using tube rectos. SS rectifiers makes a lot of sense in a 100W amp.

"DC stand off voltage" equals "elevated heater". Google will get lots of hits on that phrase.

[Willabe]

I'll start reading.

Take your time to let it sink in. I would think it's safe to say that many of the guys here (and on other sites) have read and re-read the same books to let it sink in.

I changed one of the caps from a 40uf to a 20uf. I think its a little too bassy now.

That's probably not why it's too bassy now. All you did was increase the B+ filtering a little. You can easily take out some or any amount of bass you think you need to other ways. First place to look might be any pre amp tube gain stage's cathode's by pass cap. Many times it would be a value of say 25uF, take it down to say 10uF, or 2uF. It will make a difference in the bass that is passed from gain stage to gain stage. Try 1 gain stage first and if it's not enough try a second.

A very well respected fellow member here, Tubenit has done this to shape the tone of many of his amp build's (among many here also) and has posted many different amp builds with _Great notes_ on what parts value changes did what as far as changing the tone and response of the amp.

 
                    
                         Brad        

[panhead]

DC heaters are a lot of extra work and expense becuase of the filtering requirements. Elevated DC heaters as mentioned above, are a lot simpler and if your grounding is good, quiet enough for most anyone's liking.

[nateflanigan]

Ah!  I think I spoke out of turn regarding the rectifiers, I think I was just recalling from memory some schematics with one rec and not really thinking about wether it was a tube or not, apologies.  I'd say make your life easier and just use diodes, there's lots of other things to fiddle with that would have a much bigger impact.

[stingray_65]

Just my opinions here, take it for what its worth.

lower wattage amps, to me, have a lot more "color" and respond to mods more noticeably.

A first build should copy some design proven again and again with LOTS of build documentation, examples that come to mind: 5E3 Deluxe, 18W Marshall 1974 and its variants W/WO trem,lite, brown, stout and the 5F2A Princeton.

I may be quite wrong, but it seems you want to build this amp, just to build it. Nothing wrong with that. It's more common though that people build amps to achieve a particular tone. This is a easier to achieve and gives you some sort of "goal".

NOW, all that said  we love modding designs here!

Even designing unique amps too!

Check out Tubenits info  here: http://www.el34world.com/Forum/index.php?topic=5621.0

He has designed some of the most versatile amps I've ever heard and I've built his TOS and consider it my best build ever.

A few other thoughts about amp design. I've stated this many times, Guitar amps and HiFi amps are very different creatures who's goals are not at all similar other than amplifying a small signal.

HiFi amps strive to REPRODUCE a signal FAITHFULLY. They go to extremes to eliminate possible tonal influences by using highly filter voltage supplies in the B+ rail and heaters, Over rated trannies  so that under sudden shifts in signal strength do not sag the B+ voltage and the OT's give full responce to the entire audible range, tone controls, if even present give smooth flat responce.

Guitar amps strive to CREATE a new "colored signal, DISTORTING it in a controlled aurally pleasant manor. They go to extremes to influence the signals, UNDER rated trannies that sag and add compression when there are sudden signal level changes, OT's that that have narrow ranges coupled to music instument speakers that further add tonal qualities to the end  resultant. Tone controls that are grossly lopsided (the fame Fender mid range scoop).

So some of the design concepts that you have been taught as being "better" like DC heaters or stiff over filtered power supplies may not be so well suited for guitar amps.

HiFi design is more commonly taught and documented. Even Tube data sheets show voltages and common  designs that best serve HiFi applications.

Guitar amps often run tubes, power tubes especially, at voltages off the data sheet charts to achieve the "sound" we desire.

Ray

[overtone]

Very good points here already.

Drawing your own layouts in AutoCad will help both the conceptual and the later physical skills. There is a kind of continual feedback process between the planning and the building which is a rewarding path, littered with torn down builds... You have to get a feel for how to distance the critical parts, where to leave tolerances, where not to get this wire anywhere near this other thing etc. it takes a while.
But even just hand sketching out the schematic and the layout helps you to begin to take it on board.

Starting small is good advice. I find that those small Champ type circuits teach you more about the kind of differences you are interested in. The circuits with less components reveal more. There is less clutter in the way.

Good luck, tony

[jjackson7]

I have to say you've all given me a lot to think about. As it stands I have two amps that I do not particularly enjoy playing but could be good platforms for rebuilding and learning before I decide exactly the scratch build I would like to do. I have a bassman 70 that I have mentioned before. This amp is a bit of a mess right now and I think maybe a good economical project to start with would be a new turret board for that amp. I also have a Baldwin organ amp that was re-engineered by a friend to be a guitar amp. This one takes pedals well but does not stand alone guitar-cord-amp very well. Between these two I could be busy for a while and maybe get a better idea of the how and why.

Thanks again
-Jordan.

[phsyconoodler]

the grounding schemes in most vintage amps are just fine.It's usually the lead dress that causes hums.
  So you had a bassman that hummed and you think DC heaters would cure it?Doubt it very much.It was likely the way it was layed out or something a trained tech would easily spot.
  Dc heater are best reserved for a high-gain amp that has multiple gain stages that are crammed close together.
I have built many,many amps and never had any need for DC heaters or even elevated heaters.I have also never used Hoffman's layouts.They are pretty quiet from what I've heard.Never needed them myself.All my amps are quiet.
  Experience and layout technique are learned from hands-on.

[jjackson7]

Oh, I'm not sure DC heaters would cure the hum in the bassman. That was just part of the ideas I was toying with for a dream build. I'm sure given the rat's nest that is the bassman 70 (not sure if they came that way from the factory or a result of 30 years of tinkering before I got it) there are other ways to cure the problems in that amp. Whether or not that is the problem in the bassman, if AC induces 60Hz in the first gain stages then I just thought it made sense to go DC as I had seen in the Traynors I have. Now that I have done some reading (Cheers, Brad) I think DC elevation seems easy enough to implement just to cover all the bases. Even with my limited book learnin' that circuit made sense. From what I have read layout and lead dress have a lot to do with it. I have Building Valve Amplifiers by Morgan Jones; he has a lot of interesting ideas about layout and heat dissipation. Though some of the amps in the book look like they belong in a server rack. Like you said I'm hoping the experience I get from tearing the bassman down and rebuilding will give me the skills I need to easily spot/avoid problems in the future. I think this is pretty much becoming a dead thread. I'm going to get the bassman from the practice space and start to get a circuit design together. I'll start a new thread with pics if anyone is interested in seeing me fumble through the first renovation.

[Willabe]

I'm going to get the bassman from the practice space and start to get a circuit design together. I'll start a new thread with pics if anyone is interested in seeing me fumble through the first renovation.

Yep, sounds good to me.   


             Brad   

[sluckey]

Oh, I'm not sure DC heaters would cure the hum in the bassman.

There's a very easy experiment that will confirm/bust that idea. Get a 6V lantern battery from WalMart. Disconnect the PT filament leads from the filament string. Connect the 6V battery to the filament string. Does that improve the hum issue?

[jjackson7]

Easy enough. I'll definitely try it. Thanks.

[Willabe]

You can check to see if the heaters are the (biggest) problem by hooking up a 6v battery that is large enough (lantern) to handle the current draw for a little while. Disconnect the PT heater leads, tape them off so nothing will get shorted out and hook up the 6v battery. See what you find and go from there.

               Brad