And another Rocket group build - (Clips added)

[Stanz]

Just fired it up. All went well.

A question I have, the clean tone is great, but it breaks up pretty early. This is about the same as an AC-15 type amp I built which is basically an AC-30 with only two el84s. By the time the volume gets to about 9 o'clock, it is getting pretty dirty. Is this normal? I ended up removing the capacitor on the cathode for the second stage as it was simply too much gain and was breaking up from the word go.

I also added a bootstrapped master volume and power scaling. The scaling is not hooked up yet, but that is pretty straight forward. It seems the amp plays nicely, and the distortion drops if I turn the master volume down to about 2 o'clock. With it set there, the volume control stays clean up to about 10 - 11 o'clock, and gets some nice gain after that without being too much. Am I expecting too much clean out of this amp, or is it possible my definition of clean is different than others? Speakers may another variable. Playing through a Red Fang.



The voltages seem spot on with what everyone else is getting.

Voltages:

B1 B2 B3 B4 B5
295v 286v 219v 194 v 190v

Power tubes
Plates - 290v screens - 284v cathode - 9.06v

V1 (only used half)
plate - 94.5v cathode - .65v

V2
plate 194v cathode - 114v
plate 119 v cathode - .8v

V3
plates - 173v cathode - 43v

[Zippy]

A question I have, the clean tone is great, but it breaks up pretty early.

I also added a bootstrapped master volume and power scaling. The scaling is not hooked up yet, but that is pretty straight forward. It seems the amp plays nicely, and the distortion drops if I turn the master volume down to about 2 o'clock...

If you are looking for max clean, turn the master volume all the way up. That way you are getting more power amp volume without driving the preamp as much. You can then further increase the cleans from the preamp by reducing the volume control on your guitar.

[Stanz]

That I know. Which raises a question, it seems the PI is being over driven as lowering the Master volume decreases gain and cleans up the signal. That seems backwards to me. With the voltages seemingly in line with what everyone else is getting, I was not expecting it to distort so easily.

The bootstrapped MV is basically replacing the two 1Meg resistors before the PI tube with a dual ganged 1Meg pot.

[Zippy]

Hah, you've just hit on something that I was going to play with on the bench!

The 'wrecks seem to all have a balance that gets some amount of drive throughout the amp. At the risk of adding KNOBS <gasp> to a delightfully simple amplifier, it would be interesting to add a couple of "master volume(s)" to the circuit to tune the breakup. One control on either side of the phase inverter would address the issue that you note - that of PI overdrive. If you don't want the extra knobs in your build, you can certainly use trimpots to tune the amp to give you the breakup you want, where you want it. You may also adjust the cathode resistor of the cathode follower to tune the structure.

[RJ Guitars]

Just fired it up. All went well.

A question I have, the clean tone is great, but it breaks up pretty early...

V1 (only used half)

Somebody correct me if I'm way off here... (that is always a possibility).

I think we eventually reverse engineered the circuit board on the Real Rocket pre-amp and determined that V1 has two gain stages and V2 has only the cathode follower. This differs from the original Matt Taylor schematic. It is my understanding that some funky things happen when you put a gain stage and a cathode follower on the same tube?

This might be nothing, but I'm pretty sure both of my Rocket builds have V2 with only the CF on it and both gain stages on V1.

I get pretty good clean tones although both of my Rocket amps get loud fast and will break up after 9:00. They never go into fuzz out, in fact they drop into the cool zone and I go take them all the way to max without a meltdown.

I do think that a trimmer pot just before the PI might yield some interesting results...

rj

[Stanz]

RJ,

OK, I will have to check that out. The amp sounds great, but it has pretty high gain/decent drive sound before 9:00, and by 11:00 it is too muddy to really be playable. I was contemplating putting in 1K screen resistors. I have 100R in there right now. I have it on the bench ready to make that change, so maybe I will try reworking the layout first to see what happens. Should be fairly easy. By the way, I love the layout from this project. Learned a thing or two. The positioning of the tubes in accord with the circuit board just makes it really clean. I was leary at first about not using any shielded cable, but the layout is such that it isn't that far to go.

[fishy]

Is it muddy regardless of the tonestack? I run the bass ~ 9'0' clock on mine but my room tends to be a bit boxy.

I have 1k screens. I was thinking about going the other way to see what happens although one of the supposed benefits of a higher screen resistance is touch sesitivity. I'm also cautious of destroying tubes.

RJs comment on V1/V2 and the cathode follower spark some interest for me. Maybe it is worth wiring V2 just for the follower and seeing what that gets you. I don't recall anyone reporting a muddy sound and this is the only build I can recall with V1/V2 wired this way. AC30s can sound a bit muddy and maybe this is one of the important differences between the rocket and a top boost.

Pete

[Stanz]

I rewired the Rocket so that the cathode follower is alone on V2. No difference really, or at least the "too much distortion/muddy" sound is still there. Intuitively, this layout makes sense though. I have no electronics engineering background, but having the two tubes that are operating with different voltage structures separated makes sense.

I think I have narrowed it down to three variables. I have installed a bootstrapped master volume, which basically replaces the two 1Meg resistors in the PI with a dual ganged 1Meg pot. That may somehow be affecting the gain into the PI. Or, this is how the amp is supposed to sound and my expectations are different than what actually happens. And lastly, the 12AX7 tubes may be an issue.

I am able to get excellent tones from the amp and it is a joy to play. The cleans are great, especially with my guitar on the neck PU and on single coil, cut on full (more treble), and bass/treble to taste. Very sparkly, or chimey as others have described. With the cut at max (more treble) and the treble at full, "Day Tripper" sounds like, well, "Day Tripper". It's a Vox!! With the cut at half or less (less treble), I am getting some great driven sounds. The volume acts more like a gain control.

[Stanz]

I believe I have found the elusive factor, it was the tubes. The power tubes. I just received my set of Saratov EL84s from Sgt Overdrive. That was the trick. I had a new set of JJ El84s in there originally. I can crank the volume up to 1:00 with the master volume at max and it sounds great.

WOO HOO!!!

Now I just need to build my cabinet.

[fishy]

Great.
Saratovs, haven't tried those.

Any clips planned for the future? Would be great to hear it.

Pete

[RJ Guitars]

I like Saratov's, they add a lot of fullness and sweetness to my amp...

I'm thinking you might have had a bad JJ in the mix to get those weird kinda results.

Fishy - what tubes are you using?

rj

[fishy]

I have tried JJs, TADs and Seimens.

Thought the TADs were better than the JJs but neither were as good as the Seimens which sound fuller and I think they break up better too.

I have some Russian tubes from Ebay which I haven't tried in the rocket yet.

Pete

[Stanz]

Pieced together some clips that I thought showed the amp's range. I also am trying out some recently built studio gear, a tube pre-amp and a tube mic.

[Stanz]

Some more clips...

[Colossal]

Pieced together some clips that I thought showed the amp's range. I also am trying out some recently built studio gear, a tube pre-amp and a tube mic.

Stanz, I loved the Sick Again clip! That's such a great tune. You did a nice cover of it and the tone is FAT! Great work. Congratulations on your amp.