“The mhO-ron” (whisper push-pull)
This is my third amp build. My first to be plugged directly into mains power. It uses the same board layout technique as my other amps, and represents the rise from the ashes of “the gold box”, as it canibalizes the PT from its preamp. Like my other amps this one is running the tubes below the “typical operation” stated in the tube data sheets. The effect of this is a shift in frequency response toward the low end as well as lower gain and volume. Where my other low voltage amps can be played without over powering a TV set this one is about as loud as a fender champ on 1 or 2. …with a distorion box It’s just loud enough to upset my dog .
I had about as many doubts about the sucess of this one as my first amp because I designed it at the same time. It took quite a bit longer to build. partly from the metal work and partly from error discovery and correction. |
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I modeled the main circuit in LTspice by modifying the push pull EL34 amp on Duncan’s tutorial. I highly recomend playing around with this tool as it is what let me finally realize my dreams of building guitar amps. Again I sort of fudged the model like I did on the whisper -even though I used a EL84 in my model when I used 6AK6s in my amp the tone seems to be close to what the model suggested, warm asymetrical waveform. For the power supply I used Duncan’s Power Supply Designer. (I would definately be lost without that guy)
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The chassis on this amp was taken from an old RAID system that was being thrown in the trash at work (I used the large capsfrom it as well). Maybe you can tell it is quite small (another challenge) it measures 4X8X2. If I had used typical voltages for the tubes or tried to put a high gain amp in this box I would probably never stop crying from all the RF bouncing around in there. But even with the heaters referenced to ground it has no hum or buzz, I suspect the push-pull output section helps me with that.- Its certainly not because I wound my heaters wires real tight!
This uses the RS 70V line transformer for the OT and I think overall it sounds better in this amp than the simp, Most would say this is too farty or maybe un-even but I’m enjoying the crude bBLaAATTtt!!! it generates on chords, and the knarling distortion when travis picking.
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| I tried a modified “BigMuff” tone stack, agin modeled in Duncan’s TSD2. It worked, but sucked up too much gain to be usable for much more than the soldering/placement exercise. Next I tried a triod/pentode switch. It fit were I had planned to put the power lamp(black hole by the switches. It’s a bit tight (too close to the HV secondary tap on top), I think I’ll be looking for liquid tape to avoid more shocks. |
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Here are some samples of the amp:
Dry normalized sample
with Fender outboard reverb
Fully doctored recording
Ear-bleeding fully blocked distortion |
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