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Given one 12AX7 how would you run it given the rest of the amp is SS?
Given one 12AX7 how would you run it given the rest of the amp is SS?
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Old 18th May 2018, 12:47 PM   #51
Printer2 is offline Printer2  Canada
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I have enough other amp ideas I want to try, I'll probably have enough small output tube amps. I was thinking of running the heaters in series and using a 19V brick. Should give me about 30W. I have to figure out if I want it as a pedal type of enclosure or whether to make a combo.
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Old 18th May 2018, 08:05 PM   #52
Printer2 is offline Printer2  Canada
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No, the 24V is needed for the 30W. Think I will go three tubes in series for 19V and burn off the 5V. In the mean time the thing I said I was going to do today. I have a 6K6 amp that has a BF tone stack and a Tweed Volume and Tone. The BF had three 12AX7's like the Princeton Reverb but without the Reverb mixer losses. Too much gain for me, had an extra volume control in the circuit but it was just too much to set. The switch changed it to a Tweed Volume and Tone control and paralleled up two triodes as the gain stage.

I am converting the preamp section to a 5E3 Normal and Bright Volume and Tone with the switch in one position and a Bass and Treble with Volume on one channel and Tweed Volume and Tone for the other. Ignore the power amp section, or think add a Cathodyne PI and a P-P output transformer. I'm missing a 1M resistor on the lower channel coupling cap before the switch in the schematic. Couldn't notice it before could I?

Click the image to open in full size.

Click the image to open in full size.

Of course the layout I drew up is upside down as compared to the amp. I have most converted, need to do a little on the BF side. The blue jumpers on the switch is suppose to represent the switch in the down position putting the amp in 5E3 mode.
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Old 22nd May 2018, 01:03 AM   #53
Printer2 is offline Printer2  Canada
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In another thread we were debating a battery powered Princeton type of amp and I thought SS would be a little more practical, not that practicality kept me from doing oddball things. I ran with it because I had a few Class D modules and I wanted to try them out. I also have not played with Mu-amps so I thought I might try the two together. I had the tone stack in between the two stages but I felt I needed to clip the signal peaks going to the amplifier. I don't have too much time to play with this project so I just moved the tone stack after the second stage and used the second stage to clip the signal. It turned out not too bad. I decreased the coupling capacitor and added one in with a switch to bring back some bass. I had 0.1 uF originally but it muddied things up too much. I am sure I can play around with values to make this better but that is not a top priority for me at the moment. I want to add reverb yet, tremolo would be cool also.

The amp does a good job of giving the 8" speaker its money's worth running on 12V. The supply is a laptop type brick rated for 2.5A With meter on it the voltage is rock solid. I'll throw the parts on a perf board and leave some room for modifications but I think it is usable. I found I really did not care for the level of interaction from the Fender tone stack. I could dial things in but I found it a little annoying whereas I haven't as much on other projects before this one. We'll see how I feel about it after a while. As you can see I just grabbed one bag of caps and resistors, seemed to work so there you go.


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Old 28th May 2018, 12:01 AM   #54
Printer2 is offline Printer2  Canada
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Join Date: Apr 2010
Hung out at the Marshal amplifier forum and was inspired to do a schematic that goes from a plexi styled preamp to a higher gain 2204 using a four pole switch. Then I was thinking about having a Plexi channel and a lead channel that was 2204. eventually I came up with this.



Click the image to open in full size.


And with the talk of a battery powered Princeton and the 2204 preamp into a Class D amp thread I decided to jump in, I tried to find a case to build it into and the best I found at home is the following box. The top is an anodized aluminum plate from a old disc drive. I bent up and drilled some aluminum to hold the tube sockets, still have to bend the tab to be riveted to the top plate. The well worn practice of using two drawer handles as protection for the tubes. The first row of controls next to the tubes will be Gain and Volume of the Normal (low gain or warm biased Plexi) channel and the Gain and Volume for the Lead (high gain or 2204 inspired) channel.



The next row will have Treble, Mid, Bass and Reverb controls. I have a Spin chip somewhere and it can be configured as a reverb. I think I will have a send and return loop. Then the Class D module. I might do some clipping circuit before the module but that is a secondary concern. Getting the tube section working first. The high voltage module has a large heatsink on it that might get chopped since I am not drawing many watts. Two foot switches, one to bring in the gain channel and the other for the reverb. The top plate will get drilled out for the tubes and moved up to fit on the box.



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Last edited by Printer2; 28th May 2018 at 12:03 AM.
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