Parallel triodes for smoother overdrive?

[BackwardsBoB]

Has anybody here tried paralleling triodes in a pre-amp tube using separate, different cathode resistors to extend the onset of the cutoff region of the combination, smoothing the clipping? Seems obvious, but I haven't seen it.

[Chuck H]

I've been doing it with a plexi circuit for decades. I jumper the channels. One triode uses a 1k cathode R, the other a 2.7k. On an actual Marshall I use a Boss GE7 EQ set at about 10db boost to overdrive the whole thing. On my own build I have a triode on the front end for this so I don't need the floor gadgets.

To optimize exactly what you describe would mean dialing it in with a scope, which I don't have...yet. But if my experience is any indication, it works great.

Another idea (that must wait until I have a scope) that you may be interested in is to create a more symetrically clipped wave form by intentionally biasing a triode on the cool side to achieve cutoff on one side of the waveform. Then attenuate the signal to the same level as the input to that stage, and run it into another identical triode stage to clip the other side. It should give a very diode like "grind" to the distortion (without pissing off the tube mojo guys ). An all tube circuit that can be made to sound like 90's metal...Cool (think Joe Satriani or Steve Vai).

I need a scope.

Chuck

[BackwardsBoB]

If you've been doing it for years, it must at least hold promise. The architecture you describe is what I'm thinking of. I've been staring at Carvin schematics for a while, and they take lead channel cathode resistors up to 4.6K sometimes (ValveMaster), and 3.3K unbypassed (Legacy). They're much more into cutoff than saturation. They're not exactly worshipped for their lead channels though. They seem to have some kind of corporate policy against grid-stop resistors too.

I'll be using 6V6s with power transformers designed for 6L6/EL34, so I have plenty of current available for a few more bottles, and I have a hole punch set.

[Chuck H]

When I said I've been doing it for years, what I meant was that I've been jumpering the channels on stock Marshall type amps. Nothing new, but it is very like what you describe as one triode is biased cooler than the other. You really would need a scope to see if what is happening is an extended time in cutoff.

Chuck

[TheTinMan]

Has anybody here tried paralleling triodes in a pre-amp tube using separate, different cathode resistors to extend the onset of the cutoff region of the combination, smoothing the clipping? Seems obvious, but I haven't seen it.

I've thought about it but haven't seen it. A follow on idea is to add a switch to make one side "hotter" than the other and/or change the frequency response(s) by changing cathode bypass resistors.

Chip

[booj]

I think this is all covered in a 2204

[BackwardsBoB]

I think this is all covered in a 2204

The input stage in the 2204 cascades on the high-gain input, but that's different. I'm talking about two triodes with common grid input and plate resistor, but different cathode resistor values.