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Old 2nd March 2011, 02:41 PM   #1
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Default Building a Guitar amp

Hello,

I am in the process of trying to build a guitar amp. I am currently going to school for EE, so I have a decent handle on electronics. Because of this, I was originally leaning towards a SS amp, but after reading more and more I think i finally convinced myself to go for a tube or at least hybrid amp. Since i am new to vacuum tubes, I have a few questions:

1. If I go for a hybrid design, what is more important: a tube preamp or a tube power amp? I have heard conflicting views on this but no real information to back it up. any ideas?

2. Are there any nuances to using tubes that I might not be aware of? ive read the geofex FAQ, but I want to make sure im not missing something.

3. does anyone have any fairly simple schematics for tube amps that have good tone? I'm not opposed to mixing and matching preamp and power amps from different places, and also plan on making some of my own alterations to the circuits (ie 10-band EQ and potentially other effects), I'm just looking for some good starting points.

I already have 2 12" 8ohm speakers... These to be exact:
Eminence Cannabis Rex 12" Guitar Speaker, 8 Ohm, 50 Watt#

I was planning on using these unless theres a good reason not to.

If you need any other info about my plans, please let me know. I am very excited to get this project underway!

Thanks,
Matt
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Old 2nd March 2011, 05:24 PM   #2
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You will get the information you need to build your first tube guitar amp by studying what others have done. A fantastic resource is Schematic Heaven

Schematic Heaven. Where All Good Amp & Effect Designs Await Resurrection...

You need to decide on a topology, a power output goal, and output devices to achieve that power. Output transformer selection, and power supply are equaly important design blocks and somewhere in there the pre-amp selection. I always recomend a line of books called "the ultamite tone",. this will literally lead you through the process while providing more than a little background. (theory). For parts, I like Antique Electronics Supply, lots of variety. They can sell you everything you need with the possible exception of the enclosure. Those are my favorite picks and how I got started. Be patient, gather up ideas first, then gather up parts. You might consider some kind of breadboard first. This allows for the inevatable changes befor you get too far. This can actually save a lot of time in the long run. Test equipment need not be eleaborite, DMM, scope, audio source. Lastly--- beware high voltages.

Last edited by firechief; 2nd March 2011 at 05:26 PM. Reason: spelling always spelling
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Old 2nd March 2011, 05:37 PM   #3
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Hi Matt, Have you poked around Tales From The Tone Lounge; The Home Pages of Tone Lizard Amplifiers
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Old 2nd March 2011, 05:47 PM   #4
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Thanks guys! I am familiar with schematic heaven as I have used some stuff from there for pedals ive made. I have a few breadboards and plan to use them. do you know of any good resources that spell out the differences between different amp topologies? I know about A, AB and B somewhat in terms of resistors. Also, Im looking for something in the 60-100 watt range...im not too particular about wattage, more tone. thanks again!

Matt
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Old 2nd March 2011, 06:47 PM   #5
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Quote:
Also, Im looking for something in the 60-100 watt range.
A PP pair of ElectroHarmonix (EH) KT88s will yield that sort of power. Edcor's CXPP50-4-3.4K O/P trafo seems suitable working into your speaker drivers, connected in parallel.

Do you really need that kind of power? Are you planning on filling Yankee Stadium, by yourself? With 102 dB. sensitive drivers, like those you have, 2 WPC would be quite adequate for HIFI purposes, in an "average" sized listening space. Be aware that PP KT88 "finals" will require about 475 V. of B+. A mistake with that can easily get you killed.
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Old 2nd March 2011, 06:55 PM   #6
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I sugguest you start off with the Fender Tweed Champ. It'll get you a long way both learning and tonewise. Once you get it working, maybe add a tonestack and you'll have weeks of fun fiddling around with that.

Then maybe build a Plexi 6V6 or something like that. Perhaps a 18 Watter, those things are great!

It's about trying out different things, and learning as you go on. Start small, it'll be much more rewarding.
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Old 2nd March 2011, 06:59 PM   #7
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As per wattage; if you play just at home by yourself, anything past 1 or 2 watts is just extra pain in your ears (and neighbours). With a band, 20 watts will be plenty. You can get there with 6V6's or EL84's.

I play at home with amps that have EF80 power stages, for maybe 1 watt power. Still can't keep the buggers past maybe 3-4 on the (post PI) master volume. Sometimes I use a small attenuator to get the extra roar.
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Old 2nd March 2011, 07:16 PM   #8
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sorry. Those power ratings are definitely more then I need. I was basing that off of a few SS amps ive owned, but in reality I just need to play with a drummer, a bassist and maybe a couple brass instruments. It seems like I can get away with 20-30 or so watts. also, is there anywhere i can learn about the different kinds of tubes? for instance, I hear 6v6's mentioned alot. I know that these are tetrodes, but I dont really know much about what kind of performance I can expect from different tubes.
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Old 2nd March 2011, 07:23 PM   #9
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By asking for 60-100 watts in a tube amp you are limitted to a fairly small group of tubes.
There are more choices if you are willing to go to less avaiable NOS tubes, but Im thinking you should stick to devices that you can buy new. If you can start with something around 20-30 watts (or less) then there more options like 6L6 6V6 El84 ect. Lots and lots of designs out there and like folks are saying you can always "make it your own" with features, tone modifications. You should be able to keep the cost for your first cut prototype at around $200 not including fancy packaging. You already have the speakers!
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Old 2nd March 2011, 07:33 PM   #10
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also, how do you guys feel about using an SS preamp and a tube power amp? is there anything that I need to watch out for when mixing and matching like that? I like the idea of a SS preamp because I am much more comfortable with the theory, which would allow me to make some mods and actually understand the implications.
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