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Old 23rd May 2006, 03:13 PM   #1
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Question whats the best low wattage guitar amp?

Hey guys I'd like your opinion. I want a low wattage guitar amp, besides a champ which I will build also.

I want it between 1w and 5 watts, single ended ( 1 tube only )but don't want to use a 6v6.

I was thinking of using one of the following : el84 , 6aq5, 6y6, ecl86, el86, or 6bm8.



I want to be able to use relativly low plate voltages ( between 180 and 250v to keep the transformer cheap)

I don't wanna spend loads of money on this, I want it to be a sort of budget amp. I was thining about using 1 or 2 12ax7's ( 2 or 4 gain stages)


Any ideas or opinions? and does anyone know of a good el84 schematic, I was thinking about a kalamazoo amp that uses 1 el84, but I'm not very familiar with these amps other than they were made by gibson.


I would like to select an output tube first , then go to the power transformer. I found some good 190-0-190 to 250-0-250v transformers on www.tubesandmore.com for between $32 and $40 so thats in my price range.

to keep the load off my wallet, I will be ordering a few parts here and there each week, starting with the chassis and sockets and transformers.
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Old 23rd May 2006, 07:39 PM   #2
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Have you considered the AX84 project? It uses a single ended topology with a EL84 for some 5W. Proven and tested by many.

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Old 24th May 2006, 01:18 AM   #3
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yes I did look at the ax84 projects. Has anyone heard the el84 one? Looking at the schematic... it looks like its wired for either a 6v6 or an el84, not both, am I correct? Also , It looks like it uses a 6v transformer and then another one to step it up, making a dirt cheap power supply

I think I can just incorporate a tube rectifier instead of solid state... and a proper transformer. What rectifier should I use? Is a 5y3 ok?
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Old 24th May 2006, 02:03 AM   #4
Trout is offline Trout  United States
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I would concider a Fender Champ Type amp, Single 6V6, Single 12AX7.

Shop on Ebay for an old stancor transformer like This One for about $25.00

There are plenty out there, Some even cheaper. Then get a nice SE output transformer from EDCORUSA for under $20.00

Nab an old 12 inch Jensen Speaker vintage tone for miles!
I used an old 60's Motorola 12 inch Golden Voice alnico Magnet speaker pulled from a console stereo. Best sounding vintage speaker I have ever heard on a champ style amp.
Heres one I Did using that formula,
Front View
Back View
Guts
trout
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Old 24th May 2006, 02:20 AM   #5
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sweet! Gosh I wish I had the money right now or id bid on that transformer!! I have to pay insureance and don't get paid untill friday though..

anyways, I like your amp there. As far as the speaker goes , I'll figure that out later but I designed my cab for a 10', might possibly somehow be able to cram a 12 in there but it would be tight... once the polyurethane drys I'll post some pics of my cab!

as far as the opt is concerned, I think a 25 or 30 dollar one is ok, I want it to look nice too so I don't want the bobbin showing. I want an enclosed one so that I can paint it



I'm going to build a champ later by the way. I'm ordering a 13.5"x5" x"2 inch aluminum chassis from tubesandmore for this amp. The cabinet I designed is more of a testbed for different amps, and since its my first build its not super nice... but its nice. I want my champ to be an exact clone when I build it, and maybe some different deminsions. Not only that but the transformer on it costs a bit more, $52 to be exact. When I build it I'll want a chrome chassis too.. which is $70.
My cab is only 1/2" oak ply, does anyone think that will be a problem with sound? I know most amps use 3/4" but thatsa lil 'spensive for oak..
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Old 24th May 2006, 02:44 AM   #6
Enzo is offline Enzo  United States
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If you want to keep it cheap, forget the tube rectifier. Your single ended power amp curcuit will have to be class A so there will be a steady draw from the power supply. This means no tube rectifier sag. So why waste space and money? Power transformers with a rectifier winding cost more, and the extra tube and socket cost more as well. Stick with a pair of 5 cent diodes and put the savings into some other parts.

Why not find an old record player or tube table radio for an output transformer and maybe even power transformer.

For a really basic amp like this, you ought to be able to find a power transformer cheaper than $30-40, even if you buy new. Here is a trick. You can run a transformer "backwards" and it won't know the difference. Get a 6VAC transformer for the heaters, and another for the high voltage. if you apply 6VAC to the secondary of a heater transformer, then the 120VAC wil appear at its primary. Rectify that 120VAC and you get about 170VDC. If you find a 6V transformer with a split primary, wire it for 220vAC and them you get a bit over 300VDC when rectified.

In other words, your wall outlet powers only the heater transformer in your amp. Then the extra backwards transformer is wired to that 6v along with the tube heaters, and its primary winding becomes your high voltage source.

But i also have to suggest the AX84 stuff. The designs are proven, many people have built them. There will be no mysteries as to where to get the parts cheaply.


Check these out. Allied has some inexpensive power transformers in their own brand, and Allied no longer has a minimum order.

www.alliedelec.com

stock # 227-0001 has 1 amp of 6VAC and 250VAC CT at 25ma, which is plenty for a 5 watt amp. Ignoring the center tap, 250VAC rectifies to about 350VDC. The cost is $12.71.

#227-0067 has 2.5 amp of 6VAC and 460VAC CT at 50ma, and that is way more than enough for a 5 watt amp. Using the center tap, that rectifies to about 325 volts DC. It costs $18.06.

There are others, but those look like the closest to your spec.
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Old 24th May 2006, 02:56 AM   #7
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wow thanks!

you know I might do the dual transformer setup, I know how that works, but if at all possible I'd like to keep it all in one tranny.

thatsa good point about the rectifier... I mean even the classic 30 uses solid state rectification, and modded thats one heck of an amp.

I completly forgot that when running in class A it draws current all the time because the valve is always on instead of switching between two.

Doesn't this mean, since a tube rectifier is onlf half wave, that I will only requier half the voltage that a tube rectifier would? From what I see it needs 700v to make 350v, with standard diodes in a fwb I would only need a 350v transformer? (technically speaking)

speaking of which, what does the va rating on this need to be, I read somewhere that the champ's tranny was rated at 15va ( 15 watts)
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Old 24th May 2006, 07:46 AM   #8
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Only PP class-A amps draw contious current. SE designes draw up to 2x idle at full power, so you can have all the psu sag you want. However, a SS diode with a suitable reistor in series will give you almost as sweet sag as a tube rectifier. If you consider sag sweet that is. The resistors can be shorted with a switch for adjustable levels of sag giving some tonal options.
Id go for a SE amp with 6V6 tubes, no question! go to www.tdsl.duncanamps.com and find the schematics list and make a good old fender clone. cant go wrong, and it wont cost too much either.
About power transformers, it really wont cost THAT much to get a real transformer instead of reverse fitting a 115/6VAC thingy. Dont think thats where you should save money, since the PSU is a important part of the amp. For a small amp like this a small tranny will do fine.
Go here: https://secure.tubesandmore.com/ and get the output tranny for a fender champ, and power tranny for either same or a BluesJr. not expencive.
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Old 24th May 2006, 03:55 PM   #9
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well adding up all the parts buying from there its going to cost me 180-200 dollars easily...

will the one on ebay work? It says 700vct @ 90ma, thats 350v-0-350v @ 45ma isn't it? considering thats each side... that gives me 20ma more current than a fender replacment, and the heater taps are all 1 amp higher, so the transformer should run pretty cool shouldn't it ?
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Old 24th May 2006, 04:45 PM   #10
poobah is offline poobah  United States
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Follow Trout on this...

He has made some sweet little amps... I think he has posted some MP3's you can audition!

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