Author Topic: Designing a two-stage tube circuit with compressive cathode follower ala merlinb  (Read 12313 times)

tubegeek

This is what's built right now:




« Last Edit: October 04, 2019, 04:51:16 AM by tubegeek »
"The first four times, we figured it was an isolated incident." - Angry Pete

tubegeek

So a few of my design parameters have gone by the wayside:

Some design goals and parameters:

A) To design a two-stage tube circuit including a gain stage, direct coupled into a very compressive, soft clipping cathode follower, as described in Merlin’s book. Essentially to replicate the Bassman-style circuit's tonal qualities, using different tubes suitable for a very small build.
 
B) To use subminiature dual triodes I have on hand: 6N16b.
Well, I'm using one of those, plus one 6N17b which I went and bought.
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C) To use a small 12V:120V power transformer on hand, fed by a 120V:12V wall wart. In other words, a simple linear power supply design. The 12V will feed the heaters and then the stepped-up 120V will be rectified, for a B+ voltage of approximately 160V DC after filtering.

"The first four times, we figured it was an isolated incident." - Angry Pete

Ben N

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That looks SO cool. I love the tilt+mids tone stack in the middle. Any luck on taming the gain? Puzzling that you have so much without a single cathode bypass cap and 60k plates. Is the goal a dirt box or more of a full-range preamp?

tubegeek

That looks SO cool. I love the tilt+mids tone stack in the middle.

Thanks! It *IS* cool! That stack is another of merlinb's developments, he calls it the "Bone Ray" tone stack, rather cryptically. I tried to get him to explain the name but he's being opaque on that one. I had a chance to play around with it a bit yesterday and it does quite a lot. I will plug it into my interface and record some stuff in a bit (maybe not today, busy-ish day) and post a sound sample. I want to do that anyway so I look at the waveforms it's outputting.
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Any luck on taming the gain? Puzzling that you have so much without a single cathode bypass cap and 60k plates. Is the goal a dirt box or more of a full-range preamp?

Well, sort of inbetween. I wanted to make just a preamp that would illustrate the round-clipping effect of the Bassman arrangement, and then I found that it was a little too boisterous without any tone stack so I got One More Feature, and I also liked the sound of it without the tone stack so I might add a tone stack lift switch.... Experiencing some mission creep. With the Level control after the stack there is plenty of control of the insanity, including some pretty rough dirt (but that is probably coming from overloading my amp, not internally.)

Once I get it boxed up safely I'm going to bring it to my pal's guitar shop, let them mess with it and and see what they think of it. Right now it's all hanging off an open top plate and the noise situation is actually pretty good.
"The first four times, we figured it was an isolated incident." - Angry Pete