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Old 2nd July 2011, 09:09 PM   #421
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The deadline for submission of your circuits and (hopefully) photos is October 30th of this year.....I did not realize the date was extended, I must have missed that.
This is the first that I have heard of it too, but several have pointed out that it didn't jive with Edcors long delivery times. Aug 15 was rather tight for me especially with all the "stuff" going on in my life now.

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Have you looked our political "leaders" and corporate or banking CEO's lately?

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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.
I also stated that I could build a better "minimalist" guitar amp that could be sold in kit form for $69 too. Maybe I'll look into that too.

Speaking of stuff going on, my mother in law has been fighting cancer for 4 years. This has resulted in my wife being gone more than she was here. The moment that we all knew would come has arrived. While I was typing this post Sherri called to say that her mother has passed away. I'll be leaving town for an uncertain period of time and I'll get back to this when I return.
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Old 2nd July 2011, 09:55 PM   #422
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Originally Posted by tubelab.com View Post
I also stated that I could build a better "minimalist" guitar amp that could be sold in kit form for $69 too. Maybe I'll look into that too.
I think that is what bugged us. The price was no problem if you get something a little more than a toy.
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Old 3rd July 2011, 02:18 AM   #423
TheGimp is offline TheGimp  United States
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Had to replace rear brakes on the truck today, Yesterday I don't even remember but I know I was not in the garage. Tomorrow I promised to do a cook-out and go to "Jonesboro Days"

I've busted the $100 limit and pushed back below it by looking for cheaper sources.

I pretty much have given up on the 1W SE amp as it just doesn't have enough Umph for the cheap speakers I want to use.

I'm up to amp design #5 or #6 running three tubes with PP output getting around 2W. I need to settle on a design soon if I'm going to actually build a finished amp.

If I only breadboard it and make an MP3, does it count? Still waiting on back-ordered transformers. They shipped Wednesday but didn't make it before the holiday so I don't expect to see them till Tuesday.

Current design is at $99+change. $99.99 is less than $100 so it is in.
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Old 3rd July 2011, 02:40 AM   #424
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I'm up to amp design #5 or #6 running three tubes with PP output getting around 2W. I need to settle on a design soon if I'm going to actually build a finished amp.
Note the change in deadline date.

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I pretty much have given up on the 1W SE amp as it just doesn't have enough Umph for the cheap speakers I want to use.
I gave up on my 5 tube design using old radio tubes. I tried it with a 6 inch speaker and it is nowhere near loud enough, and doesn't have enough gain to scream. I think that the power amp might do OK on 150 volts of B+ but the preamp needs more voltage. I decided to connect the whole thing up to a variable power supply and crank it up. It started sounding pretty good at the point it blew up, which was about 300 volts. One of the 6CU5's expired with no warning, no glow, no sparks, no emission either.

The next design will be capable of using several different output tubes and run them at 320 volts. One possibility is a 6BQ6GT sized sweep tube. That should rock!

I got a bunch of real cheap transformers to test as P-P OPT's, but that will have to wait until I return.
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Old 3rd July 2011, 03:30 AM   #425
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The post about the mid august deadline has been there since at least two weeks ago. I think I saw it when I returned from Key West about the 12th.

What it does not say is how we are supposed to post our demo, when it should be posted to be there in time for voting, etc.

I figure the demo should be on line by Aug 5th to have time for people to judge it.

The recommended operating point of the tubes I'm using is 220V, so I started at 250V and cranked it up till it was beyond the maximum rating (300V). At 325 they seem to be holding their own with no indication of red plating. I've tried two manufacturers and a Russian equivalent and all work fine at 325, so I'll probably crank them till something gives.

My biggest problem is my tendency to keep tweaking the operating points to see how it effects the sound and harmonic spectrum.
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Old 3rd July 2011, 03:39 AM   #426
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Originally Posted by TheGimp View Post
Had to replace rear brakes on the truck today, Yesterday I don't even remember but I know I was not in the garage. Tomorrow I promised to do a cook-out and go to "Jonesboro Days"

I've busted the $100 limit and pushed back below it by looking for cheaper sources.

I pretty much have given up on the 1W SE amp as it just doesn't have enough Umph for the cheap speakers I want to use.

I'm up to amp design #5 or #6 running three tubes with PP output getting around 2W. I need to settle on a design soon if I'm going to actually build a finished amp.

If I only breadboard it and make an MP3, does it count? Still waiting on back-ordered transformers. They shipped Wednesday but didn't make it before the holiday so I don't expect to see them till Tuesday.

Current design is at $99+change. $99.99 is less than $100 so it is in.
Glad to see another mess of wires. I am not as embarrassed by my picture now.
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Old 3rd July 2011, 04:10 AM   #427
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350V and 375V were not very interesting after 20 minutes so I cranked it up a bit.

Seems applying 410V to tubes designed for 300V max, along with 16W plate dissipation on a 4W rated tube may result in faulty operation.

Although, after I killed power and let it set for a while and then powered it back up at 250 It seemed to run fine. They never did red plate, but one tube did start flashing.
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Old 3rd July 2011, 04:13 AM   #428
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The post about the mid august deadline has been there since at least two weeks ago.
Yes it has, but the one that moves the deadline out to October just appeared today. There was a question about the rules to which I replyed that they had been discussed, but never clearly listed. SO.....see post #419.

The deadline change is good since I bought a plane ticket to Pittsburgh this afternoon for a tomorrow morning flight with no firm return date. That will be determined by how loud the boss yells when he finds out I'm not there Tuesday morning.
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Old 3rd July 2011, 04:30 AM   #429
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I think I exceeded the 600V max plate voltage rating. I get over 500V peak with 325V B+ and max output. Best to hold it to a 325V B+.

George, Sorry to hear you need to make such plans. Take care traveling. You, Sherry(sp?) and your family are in our prayers.
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Old 3rd July 2011, 04:48 AM   #430
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Sorry about the confusion concerning the completion date. I put this at the end of my post #332 --

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There seems to be a time-crunch for several people involving shipping delays and 'real-life' obligations. If there is general agreement that we should extend the time allowed for completion of the amps, let's do so. My hope is that this thread will ultimately produce a good, inexpensive amp which anyone with basic skills could successfully duplicate.
If there's no objection, how about pushing the deadline out a couple months, perhaps to the end of October, or beyond?
-- and within the hour, I was quoted and had agreement:

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No argument here.
If there are any more significant changes, I'll put them in a bulleted separate post, in bold caps, so they don't get lost in the shuffle.

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

In other news, I have my pentode preamp section up and running. It's working quite well with several tubes, including the 12SJ7 and 6AU6. It looks best on the scope, though, with an old type 77 pre-octal tube. Maybe I'll wind up with an amp that's REALLY retro, and only sounds good with a pre-WWII lap-steel guitar...

Last edited by bst; 3rd July 2011 at 04:51 AM.
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