Anyone try the "Hazen mod" to G3 supressor grid

[planet10]

There was however another thread here about a year ago where the poster claimed that a small negative voltage applied to G3 on an EL34 worked magic for the sound. It made the grid "dissapear". I never got around to trying it, although some of his other claims had some technical merit.

This is a mod Bill Perkins (PEARL) has suggested to me for years (not having a workin gEL34 amp i never tried it). He suggested a 3.5 V 1/2 AA cell.

dave

 

[Davec113]

Anyone have any further updates on the Hazen mod or the Bill Perkins mod Dave mentioned?

I have a Simple SE running el34s in triode mode, so this is interesting.

Is there any danger to experimenting with this? If I were to do this, would cutting the trace from g3 to cathode on the pcb, then wiring in a cap using the pins on the tube socket on the underside of the pcb be the right way to perform the mod? Is there a preferred way to cut a trace?

 

[Duo]

There should be no more danger doing this in your case than the others mentioned here.

Cutting of traces is fairly simple; I just make a pair of slits in the trace with a razor knife and then scrape the trace between the slits off of the board leaving a bare gap. I usually make the gap about 1/16" long but if I expect 1kV or more then I start getting closer to 1/4".

After cutting it's as simple as soldering the desired component either right to the trace across the cut or to its terminations wherever you choose.

 

[GMuffley]

It seems as if the Hazen mod is not so new after all. Sid Smith used a .22mfd cap from the suppressor grid to the cathode back in the early 60s on the Marantz 8B amp.

 

[pointy]

back then if I remember right the invisible G3 was meant to be because of some kind of phase shift between the G1and the G3.

 

[jjman]

I read about this a few years ago. It made sense to me at the time. But I don't remember the specific rational. I think the premise was that it would give the stray electrons a place to go so they don't hit the plate "late." Or did I make that up?

 

[jammons1]

I got another way to look at this Hazen Mod. I think what is happening is the Surpressor grid is being used as something different. The amp we are looking at is a cathode bias topology, and the cathode resistor develops the bias voltage at 0 signal input. Take for instance a positive swing on the grid. As the the grid goes positive, more current is drawn though the cathode resistor and the voltage developed accross the Rc goes up right along with the positive swing of the input signal on the grid. The difference in potential (think vectors not DC values) is a little less than if the cathode voltage would just stay constant. In effect this causes a little compression in the signal. Guitarists love this little compression in their 12 watt amps (cool tone?) That is also why we put a capacitor accross the cathode resitor to minimize this compression effect.
If you are with me so far, you got guts. My old Navy electronics knowledge was from decades ago.
If you can agree to the compression effect on cathode biased amps, then what would happen if I Added another cap at the cathode in series with the cathode capacitor?
The opposite would be felt on the other side of the new capacitor. rather that an out of phase change that would cause compression, we would feel an in phase change right along with the positive input signal.

Finally, the surpressor grid was never engineered to act as a control grid so I think it would have minimal effect. But maybe just enough to counter the compression in the cathode circuit.

So what i propose is the opposite of compression is being felt on the suppressor grid.