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Old 5th April 2011, 11:12 PM   #1
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Default SE P-P guitar amp.

Looking at building two guitar amps in one chassis, one P-P and the other SE. PP will have 12AQ5's and the SE a 12T10 compactron running about 250v for about 8W and 4W. LND150 input MOSFET, solid state reverb driving a 1500 ohm tank (capacitor coupled, still to be worked out). Want to switch between either amp circuit by switching the heaters, high voltage and finally the output transformers to the speaker.

Tone stack might be a Fender mid-cut network that can be switched part or fully out or I may yet just use pots for treble, bass, and maybe midrange. May have a Tweed volume-tone control and might put in a switch to run the output sections at lower voltage. Here is a partial schematic to give an idea what it could look like. Looking for comments.

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Old 6th April 2011, 12:01 AM   #2
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Printer2,
I think you are taking on too much. Certainly what you propose could be done but it certainly could'nt be live switched between the PP and SE output stages (because of warm up times etc).
Simpler way is to use what your fellow Canadian, Kevin O'Connor calls a "Body" control. Use the PP 12AQ5 with a pot on one side of the phase splitter output to dial between 0 and 100% drive to that sides output tube. Run the output tubes well toward Class A biasing for best results. With pot at 100% you get normal PP, with pot at 0% you get SE sound.
Cheers,
Ian
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Old 6th April 2011, 01:02 AM   #3
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Too much as compared to what? This is about a month long project. The only difficulty is I am putting it in a undersized chassis. Just a blink of the eye compared to the car I was building.

The purpose is not really to have a Push Pull amp that can be futzed to operate as a SE. (My SE output transformer is physically larger than a P-P transformer rated at twice the power for a reason.) Not too concerned with switching from one mode to the other, not designing this to be a channel switching amp. Would be easier just to build the P-P amp in a cabinet and do a mini head with the 12T10 and plug the speaker into the desired amp. But that would not be very different would it?

Sometimes it is preferable to go off the beaten path just to show it can be done. Still tossing the pros and cons of combining the two. Would hate to build both in and then find I never use the one. For now I am just entertaining the concept.
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Old 6th April 2011, 01:11 AM   #4
BudP is offline BudP  United States
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If you are going to use a tight chassis have you worked out how to eliminate cross coupling between various bits of iron? Are you planning to use the same power transformer for both audio circuits? Will both circuits be on at the same time, just hooked to different speakers?

Bud
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Old 6th April 2011, 01:26 AM   #5
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Power transformer on one side of the chassis the outputs on the other along with being orientated 90 degrees in relation to each other. The two are right beside each other, not a concern as only one will be live at a time. Both circuits will not be on at the same time. The MOSFET on the input and the reverb will be. Both amps are switched one at a time to the same speaker.
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Old 6th April 2011, 01:35 AM   #6
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You can save some parts if to add switch to ground from grid of the upper pentode, converting it such a way into a constant current source that compensates magnetizing of output transformer, the same time turning phase splitter into a plain cathode follower.
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Old 6th April 2011, 02:10 AM   #7
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Quote:
Originally Posted by Wavebourn View Post
You can save some parts if to add switch to ground from grid of the upper pentode, converting it such a way into a constant current source that compensates magnetizing of output transformer, the same time turning phase splitter into a plain cathode follower.
Not a bad idea but then what would I do with my stash of 12T10's? I have five of them that I want to use. If I use the P-P section to give me my SE output I will have to find a use for all those tubes and the SE transformer I have. See my dilemma? I could get a SE flavor using the P-P side but then I would still have to build an amp with the 12T10.
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Old 6th April 2011, 02:24 AM   #8
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Hmmm..., you have some problems.

May be build it, and sell to buy some new parts?
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Old 6th April 2011, 02:45 AM   #9
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Parts are cheap. No reason to sell. Just only so much room to store stuff.
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Old 7th April 2011, 12:17 AM   #10
Enzo is offline Enzo  United States
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I see, they mainly want to talk you out of it rather than into it.


try it over at www.music-electronics-forum.com/forums, what the heck?
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