220k phase inverter feed on a rocket...

[azatplayer]

...whats the point of it?

The treble return to phase inverter has that 220k then hits the .047 entry into the LTP. Whats it there for? I dont see it on any other amps. Is it attenuating the signal?

I know ive read the explanation here before months ago, but wasnt taking notice then.

Im curious because im doing a new build based on a rocket, and ive been wondering what to do with that extra triode. So, if i use it as another channel, im looking at the different ways of bringing them back together. Whether mixing them before the gain stage or at the PI. If i bring them back in at the PI, then i would prolly use a pair of 270K's in.

Sound ok?

[guitardude57]

This resistor like mix resistors, is a interstage attenuator. The value can be from 680K to 0K depending on how much gain you want to reduce.

[dave g]

If you just leave it in there without another resistor to ground afterwards (to form a divider), it's not doing much attenuation since the input impedance of the LTP PI is on the order of several megs. What it seems to do is change the clipping characteristics of the PI, as it increases the clamping effect of the PI due to the voltage drop across it when the PI is driven into grid conduction.

Personally, I prefer adding an extra 220k to ground to form a divider. By doing this, you don't have to drive the PI and output tubes as hard before you start clipping the 2nd preamp stage. I find that the output tubes get clipped a little too hard for my taste in the stock schematic.

[rfgordon]

dave g has a good point on the divider there. You can really tailor the touch of the amp by tweaking the resistor to ground.

If you look at a Rocket schematic/layout and compare it to that of the Matchless Lightning, you'll see one of the few differences is the voltage divider there in the Matchless. You could put a trim pot there for flexibility.

[RJ Guitars]

dave g has a good point on the divider there. You can really tailor the touch of the amp by tweaking the resistor to ground.

If you look at a Rocket schematic/layout and compare it to that of the Matchless Lightning, you'll see one of the few differences is the voltage divider there in the Matchless. You could put a trim pot there for flexibility.

My buddy Zippy came up with a catchy name for the variable implementation of this idea. He calls it the "Phase Inverter Gain" control - AKA the "PIG" control. If you put a pot into the circuit here you can dial it it from clean to dirty, making the "PIG" title even a bit more apropos. The details are in an old thread on tweaks for the rocket amps.

If you want to go back even a bit further you'll find it in the Trainwreck pages as one form of a master volume control.

thanks,

rj

[azatplayer]

I tried the 100k from the lightning, but it attenuated heaps and dirtied things up.
Went to a 470k and was much better but still not quite .
Ended up with a meg R, and it it pretty great. Also found the dc that was in my treble pot, damn cap feeding the PI. I changed all the caps out trying to locate it, seems i had two bad ones in that spot in a row. That or im a bit rough on caps...
Ive made a few changes to this amp, and this last one coupled to the rest is really good. Cheers guys.

[Rick]

For the 100K, you are speaking of the resistor to ground right? The one from the middle treb connection to PI is 220K in a Lightning. I went direct leaving the 100K to ground and left out the 220K and the amp is wild with a rich melted dripping liquidy class A type distortion. I may just leave it that way if the buyer can dig that tone. It does seem pretty addicting. If you back off the volume and guitar volume it seems to clean up enough but maybe not for some. I have found it to be the best tone out of the lightning so far on this one anyway.

[Structo]

I've been trying to catch up on my Rocket theory.
So are the majority of you Rocket guys using the voltage divider there?
Instead of just the 220K grid resistor you are also adding a grid leak resistor to ground?

Or is that straying too far afield from Ken's intent?

[rooster]

I can answer that one, Tom. Remember when 2Tone told us about what Ken had come up with, all in attempts of duplicating the actual AC30 circuit? This was the 220K shunt to ground right off the 220K grid resistor (I call this 'grid resistor' an attenuating or blocking resistor, BTW, based on function. And it was used in the AC30 to separate the bleed of the two channels coming into that side of the PI, just like on a BF Fender pretty much.) ..Any, 2Tone said he added this and made it switchable, but ultimately liked the Rocket better WITHOUT the 220K shunted to ground.

So, no then, I have not done this in my Rocket builds - nor do I think anybody here is adding it to theirs. But I do appreciate that Ken thought enough about it to contact 2Tone and suggest he add it to his amp.

[Structo]

So if I understand you, the 220K grid resistor is fine in the amp.

The grid leak 220K or so to ground is not desirable?

[rooster]

Yeah, that's right.

....But I am not saying that the 220K to ground is a bad idea in the Rocket because, afterall, this is the AC30TB circuit - and I do like an AC30TB that is runnin right, as did Ken apparently.

It was 2Tone who actually tried it (adding the 220K to ground) in his original Rocket - at Ken's suggestion - and decided he preferred the stock Rocket.