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DIY Stompboxes => Building your own stompbox => Topic started by: trad3mark on March 04, 2015, 04:00:51 PM

Title: 6N16B Tube as an overdrive?
Post by: trad3mark on March 04, 2015, 04:00:51 PM
Hello folks,

I'm working on a bit of an ambitious project. I'm trying to make an overdrive using a 6N16B tube. So far, I'm using a nixie SMPS to get anode voltages (110V from 9V seems safe, right?) and an LM714T to get to 6.27V for the heaters. That all seems to be fine, I think!

As far as the actual design of the circuit goes, there's a big difference between what I would like to do, and what I actually can do. The biggest thing with this is that I want to keep it in a small box, so it's just gonna be 1 tube.

In an ideal world, it would be 2 separately controlled gain stages, each giving a lot of gain. A sort of tube version of the super-duper 2-in-1. However, the mu on this is supposed to be 25-30, so I can't see that happening realistically.

So instead, I'd like to have a simple 3-knob boost/drive. The thing is, I'm having a lot of difficulty getting any sort of gain out of it whatsoever. I'm not getting anything more than about 10% louder than the clean signal. I've checked the pins a few times now, and I'm fairly sure I have them right, although I've made that mistake many times before. If someone has a suitably gainy circuit, I can verify that I have the pins right. Failing that, tips on getting lots and lots of gain out of this would be very helpful.

Blank slate on this one.
Title: Re: 6N16B Tube as an overdrive?
Post by: midwayfair on March 04, 2015, 04:18:10 PM
Schematic, please.
Title: Re: 6N16B Tube as an overdrive?
Post by: trad3mark on March 04, 2015, 04:55:44 PM
Schematic, please.

(http://i57.tinypic.com/35le07a.jpg)

that's the current gain stage I'm running with. The second is the exact same.
Title: Re: 6N16B Tube as an overdrive?
Post by: midwayfair on March 04, 2015, 05:38:15 PM
And you only have one?

Well, no wonder.

First, you need to bypass the cathode with a capacitor. In this case, it will add a huge gain boost because your resistor is 6k2. 22uF is common.

Second, your guitar signal alone is probably not large enough to overdrive this. You need another gain stage. Put a MOSFET booster in front in addition to the cathode bypass cap and you'll get plenty of distortion.
Title: Re: 6N16B Tube as an overdrive?
Post by: thelonious on March 04, 2015, 08:16:27 PM
you need to bypass the cathode with a capacitor.

+1. Here's a schem that gtudoran posted over at the other forum, just for reference/comparison. Check out the plate and cathode resistor values.
(http://i.imgur.com/1sV0Lpu.jpg)

He is running his at higher voltages, of course, which will affect your values. But it might sound good in a starved plate condition... try it and see.
Title: Re: 6N16B Tube as an overdrive?
Post by: MetalGuy on March 05, 2015, 04:40:55 PM
I can tell from experience that these tubes run better on higher voltages of up to 200V. This one doesn't have much gain by itself so if you need a descent overdrive you'll need couple of tubes for that.
Title: Re: 6N16B Tube as an overdrive?
Post by: PRR on March 05, 2015, 09:21:54 PM
"In General", it takes 1V input to get a tube to just-clip, several Volts to get CLIPPING.

Since raw guitar is less than a volt, and you really want decays below 50mV to clip, guitar-into-tube is not a satisfactory fuzz.

That's with cathode bypassed. Not bypassing the cathode resistor cuts gain in half and doubles the input needed to get distortion.

Fully bypassed the gain of the tube is maybe 20? So two stages (one to boost, one to distort) will still be marginal.

And much "good distortion" depends on both-ways action. Back-to-back diodes, or two inverting stages with some loss between.

I'd put an op-amp in there. Its gain may have to be 10 or 100, possibly more than one tube stage can give.

And this 6N16B is about the MOST linear tube I have seen. I would not expect much flavor until it rail-slams.

> I want to keep it in a small box

A design decision which I have USUALLY regretted. Heat-build-up, difficult to modify/tweak, impossible to debug. IMHO you should get a bigger box.
Title: Re: 6N16B Tube as an overdrive?
Post by: Renegadrian on March 16, 2015, 06:26:14 PM
I got 4 6n16b in front of me right now, waiting to be used...
don't try to use more than 100V, I read in the DS that is the maximum anode voltage...200V?! no good!!!

Also, try to use the "standard" values (cathode resistor 470r<->2.7k, cathode cap 680n<->47, anode res. 33k<->220k, output cap 22n<->100n)