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Old 15th June 2011, 02:01 PM   #91
AJT is offline AJT  Philippines
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i make all irons used in all my guitar amp builds.....importing edcors and hammonds are simply too impractical for me...
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Old 15th June 2011, 02:34 PM   #92
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If this challenge were an attempt to better the belittled amp that started it, then it would be a challenge to see who could build the LOWEST COST MINIMALLY USEABLE TUBE GUITAR PRACTICE AMP. Since it is not, and since no one has simply pointed to some (other) obvious candidate for that distinction, I must continue to believe that the amp which started this thread, despite some of the rather caustic (yet unsupported) comments demeaning it, does, in fact, hold that distinction. Pending revision, I will hasten to humbly admit of course.
Mr. Tubekit has some very valid points. BUT, I distinctly detected a challenge in his original posting prompting my two word response:

Quote:
You can't build a guitar amp for less than this. Not no way. Not no how.
Quote:
Wanna bet?
I have been building audio amplifiers for nearly 50 years. I design products for a major corporation, and for Tubelab, and for other small time electronics ventures. I am fully aware of how to cost out a potential product. I know that "building" and "designing a product for sale" are two totally different things. But the statement made was "You can't build a guitar amp for less than this." I KNOW that I can, using all new parts purchased from reputable sources. If I didn't I wouldn't have typed my two word response.

The person who started the original thread had asked for an amp design that he could build for his friends. This is a DIY forum and he offered to put up some of his own money to spark some creativity and so far it has worked in a big way. Since it IS his money he is free to make the rules and specify the amp HE wants. We are free to accept the challenge or ignore it. The diyAudio community will get a lot of fresh ideas, and maybe some tested and publicly demonstrated units for people to build. That's what this section of the forum is all about.

Quote:
But we're here, now. Okay, I, too, will take YOUR challenge, THIS challenge, the simpler one that THIS thread is about -- the great-sounding guitar amp for less than $100 challenge -- PROVIDED THAT all parts except the chassis, cabinet and speaker must be NEW or NOS parts readily available to everyone and priced at today's prices and the audio path must be ALL-TUBE.
As pointed out, the lead times associated with getting new parts delivered especially when customs is involved doesn't work with an 8 week schedule. It also precludes designing with fomr vendors parts (Edcor) due to their drlivery times. Accept that some people here will use parts that they have on hand. We are not building "for sale" amplifiers here. You WILL see documentation on any of my designs detailing exactly where to buy each part and how much it costs. I have done this on all Tubelab designs for the past 7 years whether they wind up for sale or not. It is possible that some or all of my designs might wind up for sale, I will not deny that. I have already purchased some parts that I have at hand in order to be able to provide a receipt to verify the availability and purchase price.

Quote:
You want to use a 12AX7? At today's prices??? And what will you leave out in exchange for that luxury?
Yes, it will be impossible to use a 12AX7 even though it is the defacto standard in guitar amps today. If you are designing an amp for commercial sale as a finished product (not a kit) you must use tubes that a musician can buy in a music store. We are not building for that market, so check out the dollar menu at some of the internet tube vendors, call them to verify ample stock before using them. There ARE acceptable alternatives to the 12AX7.

Quote:
Keep in mind that after one has created it, one has to sell it.....This means that SOMEONE has to put the parts in a bag, count them, put the bag in a box, make the shipping labels, (pay ebay and paypal) and ship the things -- all for the quoted price, of course. (NOTE: If anyone tires of this after two weeks, it doesn't count. The customers can have no confidence in its value after such a betrayal.)

That is not the point of this entire forum. It is about sharing ideas such that others can learn from your endeavors. Many may choose to duplicate your effort exactly, while just as many will morph it into something that they really want. I know all about selling boards, kits, and parts. I have been doing it for 30 years. I have been posting to this forum for about 6 years. You don't see me selling anything from this forum. Even the Tubelab forum is about support and modding.

As moderators SY and pinkmouse pointed out attempting to sell product from the technical side of this forum just irritates the moderators. Open a thread in the vendors bazaar and sell all you want, that's what it's for.

Quote:
Show us some schematics, give some helpful circuit design tips
If your stuff is good other people will sell it for you. It's called viral marketing. Wan't to sell your amp kits, create a Youtube video of someone playing it, maybe another of it being built, and state that in your Ebay ad. If the amp sounds good, and looks reasonable people will buy it. Wan't to sell them here, post all your design stuff, let people build their own or but the parts kit from you. Discuss it all you want. If it rocks, they will come......

Quote:
If this challenge were an attempt to better the belittled amp that started it, then it would be a challenge to see who could build the LOWEST COST MINIMALLY USEABLE TUBE GUITAR PRACTICE AMP. Since it is not, and since no one has simply pointed to some (other) obvious candidate for that distinction, I must continue to believe that the amp which started this thread, despite some of the rather caustic (yet unsupported) comments demeaning it, does, in fact, hold that distinction......... JUST AS SOON AS ONE OF YOU ABLE GENTS CREATES AN AMP THAT BETTERS IT AND MAKES IT AVAILABLE FOR SALE TO THE PUBLIC or, for that matter, points to ANY such real, existing item.
OK, you asked...........

Am I missing something, or is that a challenge, I just want to be sure I understand correctly. Since an amp that could SELL for $69 without cabinet or speaker also qualifies for the hundred buck amp, I just might have to make one.......
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Old 15th June 2011, 02:36 PM   #93
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I have to agree with Tubekit that there is a big difference between an amp that costs $100 for parts and one that can sell for $100 with vendor support. I don't see the point of trying to compete with some low cost vendor. Being oriented toward DIY here, it seems more reasonable to allow most anything goes for parts with the proviso that a builder should have some hope of finding something near equivalent. Otherwise we just have a contest to see who can find the cheapest HV and OT xfmrs.

Requiring that the tube types be available in 1000's knocks out most of the cheap or interesting tubes. I also don't see the point of making the amp at forced low wattage either. Volume control? For only a little more $ a much better amp can be made. We should be offering an alternative to $1000 boutique amps, not minimal parts amps.
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Last edited by smoking-amp; 15th June 2011 at 02:50 PM.
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Old 15th June 2011, 02:47 PM   #94
TheGimp is offline TheGimp  United States
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This was a response to SY in post 90,



If that's the case, then I have some neat line transformers that I've been itching to try as output transformers in a small amp.

"Most inovative junkbox amp", probably not, but fun any way.

Last edited by TheGimp; 15th June 2011 at 02:52 PM. Reason: Gee, you guys type fast!
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Old 15th June 2011, 03:38 PM   #95
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For a maximum bang for the buck amp, I would also open the gate wider to a hybrid design. As long as it still sounds like a tube guitar amp.

I'm thinking something along the lines of a modification to that Octode design that was around a while back. Use a tiny OT for the tube output, a couple of Compactron or dual'd 9 pin videos for tubes, sample the tube currents, and provide current copying boosters, via some Mosfets to the secondary side. The tubes and tiny OT still control the sound (voltage output) for guitar effects.

The switched capacitor OT/HV scheme would be a clear winner for ultimate low cost, but would require considerabe time and effort to perfect, both the switched OT/HV development, and then getting it to sound right for guitar effects. Much more than 8 weeks, more like 8 months to a few years. And then it would likely threaten all the OT manufacturers if it caught on.
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Old 15th June 2011, 03:40 PM   #96
Cassiel is offline Cassiel  Libya
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Quote:
Mr. Tubekit has some very valid points.
Mr. Tubelab has also some very valid points. Final word should come from
bst (OP).
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Old 15th June 2011, 03:54 PM   #97
bst is offline bst  United States
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This thread seems to have wandered a bit; let's get it back on track.

The original goal is this: design and build a really good, low-powered (5 watts or less) guitar amplifier for $100 or less.

These stipulations were added: the direct signal path must be all tube, but semiconductors may be used in the power supply and ancillary circuitry. The cost limit applies to the amplifier head only; speaker(s), chassis, and any tools or test equipment are excluded from the total cost of parts. However, the design must be reasonably safe: proper grounding, no live chassis, and ultimately intended to be used in a proper enclosure which prevents high-voltage shock hazard.

One grey area seems to center around the definition of 'currently-available parts'. The intent is simple: a person who discovers this thread 18 months from now should be able to go online and order the exact same parts used in the designs submitted. For example, if a schematic specifies a Triad N68X power transformer, it's reasonable to assume that this transformer will still be available in the months to come, from a number of retailers, and at roughly the same price. If you already have an N68X in your parts bin, it is not necessary to order another for this project – just specify a vendor and the current price they charge. The same applies to tubes, sockets, switches, and all the rest – use what you have, and give the source and price for ordering an exact duplicate part online. Shipping costs are eliminated from the total, due to extreme variability.

On the other hand, it should be obvious that the screaming hot deal you got on a rare, obsolete part could not be easily duplicated in the future, and should not be included in your final design. For example: several years ago at an estate sale, I purchased two brand-new Telefunken ELL80s, still in their cellophane-wrapped original boxes, for a dollar. It's absurd to think that everyone could easily find the same parts, for the same price. However, just because a component is no longer in production, it shouldn't be dismissed out of hand. 6W6s are no longer produced, yet they are available by the hundreds from numerous tube vendors, and would therefore be perfectly acceptable.

The greatest problem in this challenge is defining which amplifier qualifies as 'the best'. Who will use it, and what colorations do they want? Will it be used for a Martin with an acoustic pickup, or a Telecaster with multiple humbuckers buried in the neck? What size room? Which speaker(s)? What kind of music – blues, acid rock, surf punk, country classic – the variables are infinite.

Then there is the question of 'sound'. How do we evaluate it? Wav or mp3 files submitted online? There is far too much variability and subjectivity to make this a measurable criterion.

In the end, the decision will be up to each individual. My reasons for constructing a particular design will probably be different from yours. I'll be looking at flexibility and ease of modification, robustness and stability, fresh thinking, and innovative use of components. I'll be looking at schematics, and listening to sound clips. But my final vote will be given to the design which I would want to assemble.

Therefore, the votes will be tallied according to one simple question: If you had a hundred bucks to spend on a small practice amp, which of the submitted designs would you actually build?

Last edited by bst; 15th June 2011 at 04:09 PM. Reason: grammar malfunction
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Old 15th June 2011, 04:38 PM   #98
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Quote:
Originally Posted by TheGimp View Post
Even the power transformer can make a difference if there is B+ sag at full output.
And even this is not necessary. Screen grid current increase can be used for sagging, even when plate voltage is stabilized.
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Old 15th June 2011, 04:38 PM   #99
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If you had a hundred bucks to spend on a small practice amp, which of the submitted designs would you actually build?
That's exactly the point that I have been trying to make all along, but I couldn't find the right words. It is entirely up to the individual builder to make what they want, within their budget. It is up to us to provide the builder with as many viable choices as possible, with all the build information.

Maybe I am getting carried away. I have now ordered over $300 worth of parts, and I haven't done Mouser, Digikey or bought any tubes yet. I am making a giant spread sheet with parts costs, and I will sit down with some turret boards, parts, and clip leads and play. I will probably come up with several viable designs at several price points within the under $100 range. I can post the schematics, and maybe sound clips from each, but only my favorite 2 or 3 will get built. Or maybe you guys can decide which ones to build.

Quote:
If the results are to be judged by a sound clip, the winner will likely be the one using a 4x12 cab and a killer recording setup.
Have you ever played a tiny watt amp through a 4X12. Sounds kinda dead and lifeless. I ordered a cheap 6 inch Jensen and an Alnico 8 inch Jensen for sound testing. I have a 2X10 cabinet with EV speakers, but it needs at least 50 watts to come alive and likes about 200. It is eating 200 watts in the picture below.

Two pictures.

The first shows "furball construction". A quick way to find out if a circuit works. This one actually got made into a PC board but I am still waiting for the 9 pin compactron PC board sockets that are "due any day now" from China.

The second shows my last "practice guitar amp" prototype. It too is made with clip leads, but runs on 1500 volts. That is why there is a Lexan blast shield between me and the amp. There is also a fire extinguisher on the floor nearby. This little toy is entirely SE class A and put out over 200 watts. The spectrum of the output of a fully cranked chord can be seen on the PC screen. For me 200 watts is easy, 2 watts is a challenge.
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File Type: jpg LesPaulTest1c-2.jpg (314.7 KB, 327 views)
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Old 15th June 2011, 04:55 PM   #100
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I've driven an original Celestion Greenback with 3W and it sounds really nice. But the Greenback is only rated at 25W (20 for the new ones) and they are expensive. Does anyone make a lower power 12" speaker? The only one I've found is the Celestion G12 Blue and it is way pricy for me (> $250).

Since this is a bedroom amp, I would think something like the MOD 6-15 would be nice.
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