Question about Applying SUS-2 to See-saw Inverter

[makinrose]

I'm working on designing a new amp.  I've used SUS kits before and really like them but have question: When applying the SUS-2 kit to cathode bias amp with the "Old Style" See-saw Inverter is it okay to lift the grid-leak connections to ground even though one of the triodes is sending signal to the other?  Will this affect the operation of the phase inverter?  Here's link to style of inverter: http://ampwares.com/schematics/deluxe_5b3.pdf 

[K O'Connor]

Hi makinrose

There are a couple of ways to deal with this type of inverter and SUS.

The first option is to add a coupling cap into the first half of the splitter, then add a grid leak to this grid that would connect to SUS pin-4, with the 6V6 plates tied to pins 1 and 2. This controls the signal through the whole power amp.

Another option is to allow SUS to control just the grid-leak of the second 6V6 by lifting only the single nontapped grid-leak. This may result in a reduced effect.

A further option is to provide a separate path between the first and second triode and add a nontapped grid-leak for the upper 6V^, then make the standard SUS connection for a cathode-biased amp.

if you made the standard SUS connection in the Fender Deluxe 5B3, the signal to the second triode would be modulated in addition to the grids of the 6V6s, with the possibility of either a slightly reduced effect, a slightly increased effect, or something a little different altogether - certainly worth a try if only to hear what it does.

[makinrose]

Interesting...thanks! The first solution sounds the most intuitive to me but I might try the standard SUS connection just to see what it does.

I did this on a similar amp several years ago but I'd didn't try those connections. If I remember correctly that amp had a 6SJ7 pentode for the first pre-amp tube so it had lots gain. In that one I ended up with adding a grid-leak to the input of splitter which worked OK. I imagine with less gain like how I'm planning on doing now that won't work that well.

In a related topic adding a Body control to this type of splitter is really effective! That was my latest experiment with the see-saw.

Once I try a few connections of the SUS I'll report back.

[K O'Connor]

Hi makinrose

The front-end gain has no bearing on the SUS installation. What works in your favour here is the fact the PA does not have a feedback loop, which makes it nonproblematic to extend SUS around both stages (splitter + output).

have fun

[makinrose]

Kevin,
I may not have explained correctly. The first time I used a SUS didn't extend the SUS around the power amp. I treated the first triode of the splitter as a pre-amp gain stage and the SUS only modulated that. Unless I'm mistaken the signal amplitude is important to getting the effect.

[K O'Connor]

Hi makinrose

Yes, signal size into SUS influences how much effect results. So, since you have the output stage there providing both phases of signal to sample and these can be quite large signals, the effect can be a bit stronger than sampling the plate of the triode SUS is controlling the grid of.

You could sample both plates of the splitter just as easily, but the signals are weaker there.

Have fun

[makinrose]

I just wanted to report back. On what tried:

1. I try making the standard connection and did something interesting. You do get the sag effect but as you turn the control up you an almost octave type sound. It bit like what you get on certain fuzz pedals but less musical. So that connection is out.

2. The first connection suggested but adding a coupling cap and grid leak to first half of the splitter work really well. Sound great and provide lots different feels and sustain qualities. I'm going to stick with that connection.

Hopefully this post is useful if anyone else tries a SUS on this type of amp.