Soul Sonic Mercury 40 (High Gain)

soulsonic · Post by **soulsonic** » 03 Jan 2008, 22:27

This is an amplifier I'm currently building for a friend. It should be pretty interesting when finished. The preamp is something I designed when working on another amplifier that was done on a tweed Deluxe chassis and had 2 6V6 for the output. The results were very good and now I'm wanting to see it realized in a larger amplifier. I plan to run very conservative plate voltages on the tubes - I don't want the "hard" sound that comes from excessive voltages. The idea is to retain much of the characteristics of the lower powered version.

This is only a preliminary schematic, it will likely be tweaked as the build progresses.

See it bigger here:
http://www.aronnelson.com/gallery/d/184 ... h+Gain.gif

KippeKiller · Post by **KippeKiller** » 04 Jan 2008, 01:26

Hi,

looks interesting, the 200k - 1k5 combinations in the first two stages should give lots of gain, additionally no negative feedback is applied to tame the monster.
The boost is simple but surely effective, the cathodyn-PI is something i have to try out in the future.

What about the EL34's cathode-resistances, are they a secret or don't you just know them yet?
Same with the supply-voltage.
Just to have a better imagination on the sound of it.

Great work, i like such designs.

Regards

Mathias

soulsonic · Post by **soulsonic** » 04 Jan 2008, 02:02

Thanks for looking!
The previous one I built with 6V6s had plenty of gain, enough to get some serious distortion, but it worked out well enough that it was nice and smooth with minimal squishiness, and it was surprisingly stable with no oscillation problems. The cathode resistors, especially the 2K on the second stage, will likely get trimmed to taste.
I haven't decided on the Cathode Resistor values yet, as I haven't decided on the voltages yet either. They're looking like they'd probably be around 800 ohm each.

paulc · Post by **paulc** » 11 Jan 2008, 02:02

Hi soulsonic,

If i could make a suggestion try a combination bias set up on the output section. The compression that comes from cathode biased output tubes is cool, but a lot of times the large bias shift will cause a large amount of x-over distortion to take place - lots of "fizz". If you set up a neg bias supply you can then tune in the cathode resistor for just the right amount of compression that you want to hear, and then add some fixed bias into it to keep the tubes running at the right op. You'll see this done in the AC50.

Combination bias got a bad rep because of the silver face fenders, but there were several other things done to those amps that were the real problems imho.

Play around with it - it can really help sometimes.

Later, PaulC
Tim & timmy pedals

soulsonic · Post by **soulsonic** » 11 Jan 2008, 03:08

Thanks for the suggestion. I will definitely take it into consideration. My dad recommended combination bias to me once for a circuit that used a sextet of KT88s to help maintain a safe balance. Now, you have enlightened me to another application where it is useful. Since I have a bias winding available on the power transformer, I will give it a try.

John Lyons · Post by **John Lyons** » 16 Jan 2008, 16:41

Hey Martin

SIDE NOTE:

Take a look over at hoffman amps. They have a bunch of tube triode and other expressSCH symbols and stuff.

That's what you use correct?

John

soulsonic · Post by **soulsonic** » 16 Jan 2008, 19:15

John Lyons wrote: Take a look over at hoffman amps. They have a bunch of tube triode and other expressSCH symbols and stuff.

Oh yeah, that's where I first found out about ExpressSCH - that's a good forum, I used to go there alot, but I haven't visited in awhile. I've ordered some turrets and a staking tool from Mr. Hoffman before and I got good service, despite the fact that the shipping address I had it sent to was WeberVST (they apparently have some sort of feud betwixt them...).
I've downloaded their symbol library, but their tube symbols were clunky looking and potentially confusing to read. I drew the ones I'm currently using (after trying several other styles) because I wanted a tube symbol that was "clean" looking and free of any ambiguity. I'm thinking of drawing some alternative opamp symbols as well that are inspired by some I've seen in Russian schematics. My main concerns are lack of ambiguity and a clean layout.

Thanks for stopping by and checking this out!

Tube2stomp · Post by **Tube2stomp** » 04 Jul 2008, 09:56

Schem/gif are not available.
Probably been updated since

@paulc (if still around), how would you go about setting a combination bias?

Cheers

paulc · Post by **paulc** » 20 Jul 2008, 05:33

Tube2stomp wrote:Schem/gif are not available.
Probably been updated since
@paulc (if still around), how would you go about setting a combination bias?

Cheers

First you need to make a -vdc bias supply like you see in the fixed biased amps. If you don't have a tap on the tranny for this you can make one up like what's done in a 100 watt plexi. Then you use a smaller than "correct" cathode bias resistor, and add a small amount of -vdc to the grids to cool things back down to the right operating point.

In cathode biased class a/b amps there's a large change in current which causes a large bias shift that can get out of hand. A little is cool because it's part of what makes tubes sound like the do, but to much will fizz out under large signals.

Start off with the "correct" bias resistor for the type of amp being made. Then it's just a matter of trying smaller value resistors while adding the -vdc to keep things running right. What I look for is just the right amount of cathode "bounce" while keeping x-over under control. It's a taste thing - there's no "correct" ratio of resistor to -vdc.

I used this in one of the amps I designed for Heritage. The Victory (6V6's) used this.

Later, PaulC
myspace.com/paulcaudio