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Hi folks,
I have a bunch of 6au6 tubes and wanted to build something to put them to use. I looked at some EF-86 amps and also at Merlin's information regarding a pentode as a later stage in the preamp. I first built a single ended amp, just because I had mostly all the parts I needed, but also to test if the 6AU6 tubes that I have are any good.
This is the schematic of the single ended amp that I put together:
It's a bootstrapped first gain stage, just because I wanted to try that out, then a Framus style mid-scoop tone control, because I like the versatility it gives, going into the 6AU6 pentode with values as suggested by Merlin. Then finally a 6V6 single ended output stage.
It turned out cool, I am digging the sound. If I turn up the volume all the way, and lower the master volume, it gives a nice slightly crunchy sound. But it also cleans up nicely when I lower the volume and raise the master volume. It was really bright at first, and I even had a bright switch wired across the volume pot. Instead I turned that into a dull switch and raised the grid stopper on the 6v6 to 15k. The highs are tamed now, and flicking the dull switch is nice when switching between different guitars pickups. The only problem is, I I think I have to attenuate the signal a bit more before the output I think. I can't really turn the master volume up all the way, or at least I haven't found the courage to do so, because it is really, really frickin' loud about half the way up. I am already using an audio taper pot.
What's the usual approach here, use a lower value master volume pot, like 500k or 250k, or rather add a resistor in series before the grid-leak resistor of the 6V6?
Since I was overall pleased with the outcome, I proceeded to try and make a more powerful amp based on the same preamp concept.
So again, I have a bootstrapped first gain stage, into the same Framus style mid control, followed by the 6AU6 pentode, then a cathodyne PI, and finally an EL-84 push-pull output stage.
Also, I am using an IRF 820 for the cathode follower... First time I am trying this MOSFET out.
This is the schematic of the Push-Pull EL-84 amplifier with a 6au6 at the end of the preamp:
Question: do you think I will need more attenuation before the Cathodyne PI? I am thinking, if it's already too much in my first design, am I hitting the Cathodyne PI with too much signal? My tone circuit is really low loss too...
Is there something else I overlooked? Am I forgetting something?
I appreciate any comments & critique. Thanks!
Julius
I have a bunch of 6au6 tubes and wanted to build something to put them to use. I looked at some EF-86 amps and also at Merlin's information regarding a pentode as a later stage in the preamp. I first built a single ended amp, just because I had mostly all the parts I needed, but also to test if the 6AU6 tubes that I have are any good.
This is the schematic of the single ended amp that I put together:
It's a bootstrapped first gain stage, just because I wanted to try that out, then a Framus style mid-scoop tone control, because I like the versatility it gives, going into the 6AU6 pentode with values as suggested by Merlin. Then finally a 6V6 single ended output stage.
It turned out cool, I am digging the sound. If I turn up the volume all the way, and lower the master volume, it gives a nice slightly crunchy sound. But it also cleans up nicely when I lower the volume and raise the master volume. It was really bright at first, and I even had a bright switch wired across the volume pot. Instead I turned that into a dull switch and raised the grid stopper on the 6v6 to 15k. The highs are tamed now, and flicking the dull switch is nice when switching between different guitars pickups. The only problem is, I I think I have to attenuate the signal a bit more before the output I think. I can't really turn the master volume up all the way, or at least I haven't found the courage to do so, because it is really, really frickin' loud about half the way up. I am already using an audio taper pot.
What's the usual approach here, use a lower value master volume pot, like 500k or 250k, or rather add a resistor in series before the grid-leak resistor of the 6V6?
Since I was overall pleased with the outcome, I proceeded to try and make a more powerful amp based on the same preamp concept.
So again, I have a bootstrapped first gain stage, into the same Framus style mid control, followed by the 6AU6 pentode, then a cathodyne PI, and finally an EL-84 push-pull output stage.
Also, I am using an IRF 820 for the cathode follower... First time I am trying this MOSFET out.
This is the schematic of the Push-Pull EL-84 amplifier with a 6au6 at the end of the preamp:
Question: do you think I will need more attenuation before the Cathodyne PI? I am thinking, if it's already too much in my first design, am I hitting the Cathodyne PI with too much signal? My tone circuit is really low loss too...
Is there something else I overlooked? Am I forgetting something?
I appreciate any comments & critique. Thanks!
Julius
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