The Hundred-Buck Amp Challenge

[Printer2]

Originally Posted by sprinter

I'm sure that the heavy hitters here can address this better, but it's my impression that this is a sweet spot for designers in the cost/benefit equation. Going up to 15 watts or so requires much more expensive tubes, transformers, etc, etc. I'm sure that some the designs coming out of this will be conservatively rated for purposes of this contest but could be easily pushes a few watts up if you need it. I will agree that 5 watts is somewhat limiting for clean headroom, but it's still loud, especially in tube saturation.

Look at the number of commercial offerings in the 5 or 6 watt range right now. This is where it's at for home/practice/recording. Even small gigs.

And don't forget what a good speaker can do.

Yes I know, but I hate to waste excess transformer capacity.

I built a SE amp a while back with a 6AQ5 and a 8" public address speaker which sounded fine but it could not play clean loud enough for me. Distorted was another story. Probably was shy of 5W but with a good speaker it might have been ok. The reason I wanted to use the 8" I did was they are cheap and I wanted to put together a design that some kid could build for a few bucks and be happy (surprise, kind of the reasoning behind this thread). Not really complaining of the limit, after all 10 watts is not really all that much louder.

Cost wise the transformers is going to be most of my budget. Want to try the 70v transformer thing to shave a few bucks. Never tried it before so it should be interesting. I would have liked a PI but that went by the wayside to stay in the budget. I would have liked to do it with the addition of a MOSFET but they do not seem to be the flavor of the day.

[sprinter]

I built a SE amp a while back with a 6AQ5 and a 8" public address speaker which sounded fine but it could not play clean loud enough for me

This is my concern, too. These little amps seem destined for metal, although I do hear some praises for cleans in a few commercial jobs in the 150 - $200 range. I really hope some the entrants here are trying to address that end of things. I've heard it said that "you can always add dirt but you can't add clean" or something like that.

Cost wise the transformers is going to be most of my budget.

What this country needs is a good 16 ohm tube!

Or maybe a good 5Kohm speaker?

How about a Circlotron or other transformerless design? On second thought, the cost is limited to less than $2000 and it can't kill you. Darn.

[Wavebourn]

Originally Posted by sprinter

Is it even possible to build an amp at this cost that has lots of clean room but still saturates nicely when needed?

I mean the amp that will sound on 1 meter distance like a famous stage amp on 100 meter distance. The same sound.

I'm thinking maybe a gain switch or something that is labelled "Fender" on one side and "Marshall" on the other.

Yes, but there should be 2 amps in 1 box.

[sprinter]

Quote:
I'm thinking maybe a gain switch or something that is labelled "Fender" on one side and "Marshall" on the other.

Yes, but there should be 2 amps in 1 box.

To do it right, exactly so. And why not? Tubelab George is squeezing in five tubes. I don't know what he has in mind (PP or PPP I think), but it ought to be possible. It's only the cost of parts that's important here, not necessarily design simplicity.

[Printer2]

Originally Posted by Wavebourn

I'm thinking maybe a gain switch or something that is labelled "Fender" on one side and "Marshall" on the other.

Yes, but there should be 2 amps in 1 box.

Well I was not going to do that with this build, but if you guys really want it...

[Wavebourn]

As I said already, Champ will be made on one 6N17B and one 6P30B tubes. More "powerful" PP amps will use more tubes, of course, probably 2 x 6BA6 output, to simulate over-driven 6L6 clones.

[Tony]

OT: @Wavebourne, what would be the Russian equivalent of the 6CG7? thanks...

[tubelab.com]

Tubelab George is squeezing in five tubes. I don't know what he has in mind (PP or PPP I think), but it ought to be possible.

I am building a rather ordinary push pull amp. The 5 tubes are all single unit tubes, pentode input, triode gain stage to recover tone stack losses, triode PI, pair of pentode outputs. There are some rather creative tricks pulled to save money on the circuitry, so I would have it to spend on things like pots and switches. Guitar players like knobs to turn, speaking of knobs, anyone found them cheap yet?

After it is all working I plan to tweak it and change out entire stages if necessary. The spreadsheet told me that this was the best bang for the buck so I started here. There are two alternate P-P designs using multi section tubes at similar costs. I may build them all and test if I have time.

I have been making SE champ style amps going back as far as 7th grade, and I am nearly 60 now, so I doubt I will go there unless I get a wild hair........

[simon7000]

Originally Posted by Wavebourn

As I said already, Champ will be made on one 6N17B and one 6P30B tubes. More "powerful" PP amps will use more tubes, of course, probably 2 x 6BA6 output, to simulate over-driven 6L6 clones.

6BA6 is a decent choice to scale down a classic guitar amp. I am going with a directly heated cathode version.

Tone control action is an area I think is of some importance, along with modeling the distortion vs volume curves but at a lower level.

[Trout]

5W is plenty even live, throw a mic in front of it and you are good to go.

Check out the old Live Clips of the Faces, Ron Wood used an old Fender Silver Face Champ.
YouTube - ‪Rod stewart & it's the faces stay with me live uk‬‏
You can see it tucked away stage left, right behind him. 0:56 & 1:36 into the video.

Then look at cleans,
Ole Jeff Beck is using tiny amps on tour right now with Imelda May.
YouTube - ‪Jeff Beck with Imelda May-Tiger Rag (Based on a 1917 song by the Original Dixieland Jass Band)‬‏

Did the same thing on the Les Paul Tribute
YouTube - ‪Jeff Beck honors Les Paul [Best of Guitar-Tube]‬‏