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Old 2nd July 2011, 03:33 PM   #411
Cassiel is offline Cassiel  Libya
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Where's our leader? As expected after seeing that 99$ amp the morale of a few members has sunk, BST's (OP) included? Is the game still on?

To all those asking about the power limit: a triode/pentode switch or a power attenuator keeps you in the game.

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I have always had a problem with rules.
Ditto.

Last edited by Cassiel; 2nd July 2011 at 03:35 PM.
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Old 2nd July 2011, 04:18 PM   #412
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Power limits are all about the speaker.


How about we say this is supose to be a bedroom amp instead (as I seem to remember what it was to be in the first place).

Last edited by Printer2; 2nd July 2011 at 04:20 PM.
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Old 2nd July 2011, 04:19 PM   #413
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Surely for a 2watt design even a mismatched OTL design would do - eliminating the OPT completely..?
Even at 2 watts the peak currents into an 8 ohm speaker are in the 1/2 amp range. Maybe the OPT goes away, but the power transformer just got more expensive. Tubes that can pass this current tend to have hungry heaters. You are free to experiment and prove me wrong.

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Where's our leader? As expected after seeing that 99$ amp the morale of a few members has sunk, BST's (OP) included? Is the game still on?
If you want something easy, then buy the box from China, rip it up, mod the $*#@%^ out of it and post your results. It may not fit the contest, but it is a valid way to get started. Google around and you can find several cheap amps from China for less than $100.

I expected from the beginning that there will be a lot of talk but probably only a few amps built. It has always been this way. If you look at the amp design threads in the past that have several hundred posts and a dozen or more posters all talking about building an amp, only one or two actually get built.

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I have always had a problem with rules.
First off, I have yet to see a list of posted "rules". Most true contests state exact rules and judging criteria up front.

Second, this isn't about the contest. Does "winning" really matter? I have already spent over $500 on parts to "win" $100. I knew that when I posted the two words that started it all. This was the motiviting factor that got me started on something that has been in the back of my mind for a long long time.

So if you don't like the rules, build your amp your way and show us what you made. Maybe you won't get $100, but you will still get your amp, and we get to see another persons viewpoint on what their ultimate amp is. Google the guitar amp building world, 90% of the amps being built are still derivatives of the SOS. It's time for some new stuff.

Those who have followed the Tubelab designs know that there will be a PC board and one or more mosfets. I am making the prototype in modular form so that the preamp, power amp, and power supply are all designed independent of each other. So when this contest is done, the preamp will get used for something a little bit BIGGER.
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Old 2nd July 2011, 04:25 PM   #414
Trout is offline Trout  United States
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For those looking for a reasonable cost 12" speaker, I see these popped up on ebay again.
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1506268929

$12.99us

It IS an Eminence speaker, but appears to be some kind of OEM overflow unit. They seem to pop up about every 4-6 months.

The speaker specs sheets leads me to believe it is a possibly custom 12 inch version of the Legend series?



NO AFFILIATION, just a bargain I located last night.
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Old 2nd July 2011, 04:59 PM   #415
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For those looking for a reasonable cost 12" speaker......
There are two digits missing from the item number the correct # is 150626892938

The speaker is $12.99 but the shipping is also $12.99 so it is a $26 speaker. Still a reasonable price, so I bought one.
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Old 2nd July 2011, 06:03 PM   #416
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Originally Posted by tubelab.com View Post
So if you don't like the rules, build your amp your way and show us what you made. .
Just trying for a bit of humor, upfront I said I did not considered being a contender. I think we might even get more participation if we just skip the contest thing and just keep the idea of building a bedroom practice amp. Use spare parts, build it in a cardboard box (well maybe not cardboard). I will not bother searching out prices of every last part, might give the rough values of items, any more than that and it will seem like I am still at work. That takes all the fun out of it.

This thread spun off of one where someone was selling a cheap amp kit for for somewhere around $70-80 (too lazy to look it up). Some felt it not worth the money and you can do better on your own. Well it seems not as easy as first thought if you want to make something better and are paying retail. I would not spend the $70 on the advertised amp but I would spend the equal amount building mine.

I am not breaking new ground with my build, just taking ideas from other amps and incorporating them.using to come up with something playable.In the end I will be using it so I am more concerned with pleasing myself rather than anyone else at this time.
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Old 2nd July 2011, 06:06 PM   #417
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Originally Posted by tubelab.com View Post
There are two digits missing from the item number the correct # is 150626892938

The speaker is $12.99 but the shipping is also $12.99 so it is a $26 speaker. Still a reasonable price, so I bought one.
$29 for shipping (and then duty), no bargain for me.
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Old 2nd July 2011, 06:34 PM   #418
Cassiel is offline Cassiel  Libya
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Quote:
I expected from the beginning that there will be a lot of talk but probably only a few amps built.
Power stage and phase splitter finished. I'm using an SE OPT salvaged from tube radio. It has several primary tabs, 0-0.8K-1.6K-3.2K. Secondary is 3.2Ohms. My amp has a tube rectifier - Telfunken AZ11. Surprisingly I have no hum (OPT severely unbalanced), my phase splitter is a paraphase design stolen from an Ampeg amp. It's good for 6SL7's and 6SN7's. Money spent so far ~ 50 bucks. Preamp still in the designing process.

Quote:
Second, this isn't about the contest. Does "winning" really matter? I have already spent over $500 on parts to "win" $100.
It's not about the money, ancient Greek Olympic champs did only get an olive crown still they felt happy gods because of the glory and honor achieved. I want to be voted, if I win the money would go to the next legal design with the highest rank. I think this is a good idea for all of those who want to participate outside the rules.
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Old 2nd July 2011, 07:19 PM   #419
bst is offline bst  United States
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Quote:
Where's our leader? As expected after seeing that 99$ amp the morale of a few members has sunk, BST's (OP) included? Is the game still on?
Leader? Perhaps instigator would be a better term. 'Leader' implies superior knowledge and experience, and I hardly qualify on either count.

Yes, the game is still on. I never did post a hard-and-fast set of final rules, and for that I apologize. Let's call these guidelines, instead -- the intent and spirit of the challenge is pretty straightforward:

1.) The goal is to construct a low-power tube guitar amplifier, from commonly available parts, for less than $100. The total cost excludes the chassis, cabinet, and speaker, as well as the shipping cost for the parts.

2.) The intent is to develop a robust, easily-modified basic design which can be constructed by someone with basic electronic assembly skills. The design can then be modified and expanded to taste, but the basic functional circuit
needs to meet the $100 parts-cost limit. For example, I'm experimenting with a basic pentode-drive-SE pentode topology. No innovation here; just trying different combinations of off-the-shelf parts. Once I have a functioning amplifier which satisfies me, then I may play with tone stacks or component upgrades. Think of a Fender 5C1 and how it evolved -- my first objective is to build the simple version first, and have it sound good within its limitations.

3.) The deadline for submission of your circuits and (hopefully) photos is October 30th of this year. This should give people time to narrow down their design concept, and breadboard a prototype. Whether the designs fade into oblivion, or grow legs, has yet to be determined.

4.) Above all, this is supposed to be an enjoyable diversion, not work. No one gets called into the office if they decide to abandon their project. No one gets a letter of reprimand if they go over budget, or decides to go off on a completely different tangent. The original trigger for this whole thread was one person's absolute pronouncement that a better practice amplifier than his could not be built for the same price. Many people thought, and one person responded, "Wanna bet?". And the challenge was launched...

*******************************************

My own tinkering with this project has been both fun and enlightening. I've never built a guitar amplifier before, and I'm learning about a whole new genre with a very different set of criteria than amps built for accurate reproduction of recorded music. I've never used a pentode for an input stage before, and I've never purposely overdriven a tube. I've never built a minimally-sized power supply, which loses current and/or voltage regulation (sags) when the amp is driven hard. I've never used tone controls (although one won't be in my core design, I'm going to experiment with them later).

In short, I'm learning, I'm having fun, and I'm doing it on the cheap. I hope that others will do the same.
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Old 2nd July 2011, 07:50 PM   #420
Trout is offline Trout  United States
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I did not realize the date was extended, I must have missed that.

From page #1
Quote:
A poll will posted, and challenge participants will be asked to vote on the design they consider best overall. On August 15th, 2011 the winner of the design poll will have the cost of all materials for his/her amplifier reimbursed, up to the amount of $100. In addition, $250 will be donated to diyaudio.com in appreciation for providing this forum.
Maybe I can still make it.

BTW, I am working on PP 6W6BT ($3.00 ea) which gives further options for using salvage PT's combined with 12W6GT & 25W6GT.
Or it could be converted to 6V6 if desired,
The part that keeps me going over budget is the VVR which I really want to use to get it to bedroom / headphone levels easily.

I have mine partially assembled, Chassis punched, sockets mounted/wired, eyelet board made and ready to complete.

Money for winning? Heck, I would just donate it or use part for a paid membership here.

Speaker link corrected
http://cgi.ebay.com/ws/eBayISAPI.dll...m=150626892938

Last edited by Trout; 2nd July 2011 at 07:54 PM.
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