Rocket Tweaks

[RJ Guitars]

Thanks Normster! rj

[Stanz]

I put in a similar system to the VVR, except I am only bringing the power tube's plates and screens down. With cathode biased power tubes, pretty easy to do. Unlike Dana's approach, I put in a bootstrapped master to reduce the gain into the power section, as opposed to reducing the voltage supplies on all tubes. I believe he reduces his gain through the guitar.

I now call it the marriage saver control. Although my wife has this funny habit of standing about five feet directly in front of the speaker, with both fingers in her ears saying "It sure is loud." I tell her it helps keep the pests out of the house.

[Wayne]

... Although my wife has this funny habit of standing about five feet directly in front of the speaker, with both fingers in her ears saying "It sure is loud." ...

I ran into this at my last gig. "Sir, if you are finding the band too loud, why don't you go stand over there, away from the speakers?" It never seems to work that way, though

W

[RJ Guitars]

Turn that thing down - my mum used to say that all the time...

I made two tweaks using info straight out of "The Trainwreck Pages". Ken Fisher provided four ways to add a master volume.

The first I call the PIG control - Phase Inverter Gain = PIG. (I can't take credit for this acronym, it was given to me by Zippy here on the forum.) If you pad down the signal going into the phase inverter just a little bit, the amp becomes super clean. IMHO, This is implying that we are pushing the power tubes into distortion... maybe something more or different is happening, but the PIG control allows super clean and doesn't seem to mess with the tone otherwise... I need to play it more to really say. For my experiment I put a 1M pot in as the PIG control.

The second is a more traditional Master volume that backs the power tubes down. This uses a 1M dual pot and as I said, it's straight out of the book. In this case you can crank the preamp and hear the overdrive kick in at about 2 o'clock or so. it sounds good until about three o'clock, then it get's kinda fizzy. This leaves no doubt that the Rocket has the ability to make preamp distortion.

I'm not sure either of these are important things to add to a gig amp... YMMV, but they are handy diagnostic tools. I would say a fixed value would work best for the PIG, but I haven't actually measured out my favorite spot yet. With a light amount of preamp distortion the Master volume is very useful. When you dime the gain knob and squeeze the amp down with the master, it's not so pleasant of a sound.

Enjoy,

This was a lot of fun to mess with.

rj

[gahult]

Note that the Master volume Type !, 2 and 3 are labeled for pin 5 which is the Express EL34. This will be pin 2 in the Liverpool and Rocket EL 84. I'm sure this is obvious to most, but for newbies like me I had to dig around and scratch my head a bit.

Gary

[Curbdog]

RJ, I'd like to put the PIG control on the Rocket pre-amp board as a 1M Trim POT. I think I see a space for it ! Is there a little schematic available for the PIG? Thanks !!

[RJ Guitars]

RJ, I'd like to put the PIG control on the Rocket pre-amp board as a 1M Trim POT. I think I see a space for it ! Is there a little schematic available for the PIG? Thanks !!

Curbdog,

It is really simple and I'll attach a drawing... as I said this is right out of the Trainwreck pages.

As you can see from my pictures, I used shielded cable. I'm not sure that's essential, especially if you're going to do a trim pot on the board.

I was actually thinking about a switch and a fixed value resistor because I really love what this amp does as is.

rj

[RJ Guitars]

After looking at the Matchless schematic that Normster posted, it seems that the component values really are similar to the Rocket and AC-30.... just an observation.

I'm curious about voltages in these amps and I would like to know what everybody else is measuring... I have two Rocketish builds, one with Heyboer iron and the 2nd with VOX iron.

rj

-Heyboer PT- -VOX PT-
B+1 - - 320 - - 337
B+2 - - 312 - - 325
B+3 - - 234 - - 248
B+2 - - 207 - - 218
B+5 - - 202 - - 213
V1b - - - 95 - - - 90
V1a - - 128 - - 131
V2 - - - 207 - - 218
V3a - - 181 - - 196
V3b - - 182 - - 191

[funkmeblue]

sorry to be off subject.....but what is the purpose for the 220k resistor just before the phase inverter?

[dave g]

sorry to be off subject.....but what is the purpose for the 220k resistor just before the phase inverter?

That resistor is taken straight from the AC30 - it's one of the mix resistors that ties the top boost channel to the normal channel right before the PI. For whatever reason, KF decided to leave it in, even though there's no mixing going on.

[RJ Guitars]

One last tweak... nothing new here but worth mentioning. This isn't without it's discussion points including what happens to the load impedance when you remove two tubes, or as my friend skippy likes to say - add two tubes and make it the 2X power switch.

The one thing that I think is most note worthy is that the amp doesn't go through any massive change in character when you go from four tubes to two. There is a noticeable difference in volume... no it's not "half volume", but overall a more subtle change and the results are certainly enough to convince me that a two-tube Rocket can sound very cool.

Technically what is happening (for those that don't know), is that I have used two 100 ohm resistors for the cathode resistors instead of a single 100 ohm. Then by lifting the ground on one of those resistors using a toggle switch, I take two of the four power tubes out of the equation.

It's half power, not half volume and I'll let that discussion take it's course or die on it's own. If you do this, be aware that you've changed the load impedance going into your output transformer and you might want to make an impedance adjustment on the speaker side of the transformer to balance things.

rj

[Fischerman]

sorry to be off subject.....but what is the purpose for the 220k resistor just before the phase inverter?

That resistor is taken straight from the AC30 - it's one of the mix resistors that ties the top boost channel to the normal channel right before the PI. For whatever reason, KF decided to leave it in, even though there's no mixing going on.

It sounds better with the 220k than without it...the amp 'feels' better too. IMO, YMMV, etc, etc.

[guitarsnguns04]

this is a good thread...I am getting ready for my rocket build this coming week...anymore cool tweaks to consider?

[Zippy]

Tweaks...

1) In RJ's picture, there remains the opportunity to add the "Chime" switch - inserting the bypass cap on the output cathode resistor.

2) The "Strat-friendly" switch - put the two halves of V1 in parallel to add a lil' gain and complexity as well as reduce a lil' noise due to common mode noise rejection (move the second stage to V2a, cathode follower on V2b). Nothing new - it's the same thing as presented in many of the Matchless builds (see the Lightning schematic). TubeDogSmith may have hardwired it on his early Rocket build as I recall.

[Fischerman]

2) The "Strat-friendly" switch - put the two halves of V1 in parallel to add a lil' gain and complexity as well as reduce a lil' noise due to common mode noise rejection (move the second stage to V2a, cathode follower on V2b). Nothing new - it's the same thing as presented in many of the Matchless builds (see the Lightning schematic).

Steve Bench did a little article on this...the results may be a bit surprising. The article is here.

I actually did build mine like that (paralleled V1) even though I had read Steve's article beforehand. My intention was to do some testing on my own but I never did. Probably will someday.