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Old 8th July 2011, 04:26 AM   #491
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Newest design. in keeping with the low wattage bedroom amp idea I wanted to do the self-split (no phase inverter) but I also wanted some more power so I can play clean. I looked at the circuit I was using and thought with a few added parts I could convert the second triode into a Class AB with a cathodyne PI stage. Mind you that leaves me short of gain, but that was another bridge to cross later. Did the changes and tried it out. Then I started thinking (I know a dangerous thing).

Now if I add a pentode first stage I could get back my gain, that problem solved, I wanted to play with my 12AU6's anyway. Now if I use a switch and drop out the capacitor on the power tube cathodes, and then short to ground the junction of the 100k and 1.5k resistor I am back to my self-split with the PI back as a gain stage.

So rather than build two boards, one for this thread and the amp I would rather have, I get it all with adding one switch. And while I am at it, I could use the board in self-split mode, drop one tube, use a single ended output transformer, and then I have a single ended amp. I may need to adjust the output tube bias but it sure beats building another circuit if I wanted to try it.

I think this will work, I will have to try it on the weekend.

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Old 8th July 2011, 05:10 AM   #492
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Here is my amp:

YouTube - World Champion guitar amp project - parts
And here is the demo of how it sounds:

YouTube - World Champion guitar amp project -- sounds
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Old 8th July 2011, 05:18 AM   #493
ChrisA is offline ChrisA  United States
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I thought of using a pentode input also but they have a reputation of being noisy. My plan was to use one of the triode/pentode combo tubes, Pentode section is input then the triode as a phase splitter and finally a 12au7 as a power tube. It's a cheap and easy way to get gain but you have to like that sound

Transformers are really what matters. The key is finding a good one for cheap. I have and output transformers from Triode Electronics that they sell for use as a reverb pan driver in a Fender 6G15 reverb unit. The 6G15 uses one 6K6 power tube, single ended and drives an 8 ohm pan. This would make a good and cheap amp. The 7000 to 8 ohm xformers is about $15 or so and the 6K6 tube sounds lika a 6V6 but less poer and ony about $6.00. Basically use parts from a 6G15 but place a speaker where the reverb pan would go. Thhis would use two tubes and the OPT is cheap.

I have the parts on hand and I'm building a 6G15 right now. It would be easy to try it out as an amp first but I doubt I'll get it done by the deadline. Weber also sells the same transformers but I though Triode's were a bit better
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Old 8th July 2011, 06:09 AM   #494
wdcw is offline wdcw  Australia
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Thanks for the links Wavebourn,

I noticed you mentioned that people were copying original designs?
Is that part of the criteria for this challenge as I didn't read about that, mine is an original design, is that ok???

Cheers
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Old 8th July 2011, 06:17 AM   #495
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Quote:
Originally Posted by wdcw View Post
Thanks for the links Wavebourn,

I noticed you mentioned that people were copying original designs?
Is that part of the criteria for this challenge as I didn't read about that, mine is an original design, is that ok???
If people were copying original designs, that has nothing to do with this challenge. The challenge is to make the amp that is the part of the instrument and helps to produce needed sounds. The majority of "Original Designs" were looking exactly like examples from books published by manufacturers of vacuum tubes. What make them original, they intentionally had some features that made them good for electric guitars.
For example, I saw lots of Fender Champ's "Improoved Copies", but "improvements" were far from what guitarists needed to be improved. What I demonstrated today, I made the amp even worse for Hi-fi sound reproduction, but some guitar players can find it as valuable improvement.

However, another part of this challenge is to make this guitar - specific amp for less than $100 in parts.

The rest depends on imagination.
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Old 8th July 2011, 09:38 AM   #496
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Damn it sounds niceeeee.....
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Old 8th July 2011, 09:46 AM   #497
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+1 for Wavebourn's demo
BTW - what is the OPT used?
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Old 8th July 2011, 11:08 AM   #498
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Quote:
Originally Posted by wdcw View Post
Thanks for the links Wavebourn,

I noticed you mentioned that people were copying original designs?
Is that part of the criteria for this challenge as I didn't read about that, mine is an original design, is that ok???

Cheers
The whole problem is that so many people have tried to skin the same cat over the years that if someone came up with something 'new' today, it probably was done at some time before by someone else. And let us face it, there are only so many ways to string together a little amp. A two or three tube amp will look like another two or three tube amp. Now will w come up with a combination of parts and design (physical layout) that someone will look at and decide they want to build? I think that is what we are trying for here right now.

I am experimenting with 10W 70V transformers because they are a part that is readily available and cheap enough that someone, even 10 years from now will be able to use. The rest of the circuit is just standard building blocks used in guitar amps. I will tweak the values but otherwise not too much new here.
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Old 8th July 2011, 04:01 PM   #499
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Originally Posted by dovla View Post
+1 for Wavebourn's demo
BTW - what is the OPT used?
Thanks.
Both transformers come from tube radio I bought on Flea Market for $5.
The power transformer has 6.3V and 2x125V secondaries. The output tranny is 5K:8 Ohm, for 6AQ5 tube.
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Old 8th July 2011, 04:48 PM   #500
PB2 is offline PB2  United States
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Originally Posted by Printer2 View Post
I think this will work, I will have to try it on the weekend.

Click the image to open in full size.
Is the first .022uF off the first plate there to allow you to use lower voltage caps in the tone stack? It is not needed if all the caps meet the voltage spec, otherwise yes one HV cap there with say a 1 Meg bleed to gound would allow lower voltage caps in the tone stack. Also, the .022uF is in effect in series with the .1 uF and .47 uF in the tone stack at mid and low frequencies and it will dominate the reactance being of much smaller value. Fender often used .022 or .047 uF in the tone stack, did you really intend to use those big values?
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