Rocket Tweaks

[RJ Guitars]

Hey guys,

As I see all these Rocket amps show up, some from our group effort and several others from various places I see many of us have a few common tweaks that we have discovered or that have been requested.

For those without one of these amps, they are highly recommended. This is probably the best amp I have ever played through. It might be the perfect rhythm guitar amp. I don't think it really shines so much as a lead amp though.... get an express or Liverpool for that.

I'll begin with fixing a problem first, then going for some tweaks. On my Rocket I used a star grounding system but I broke the rules a bit... I also suffered for doing it. I had some residual hum caused by tying the ground on the phase inverter to the preamp ground bus... an obvious mistake now in hindsight. This caused some residual hum that I had to sort out.

So this isn't really a tweak, but a fix that gives me a place to post the latest layout for the group build. If you built with the H1c layout, you'll probably want to change the ground point on the inverter to go directly to the star.

The Rocket isn't a super high gain amp so it should be and it is super quiet as far as the noise floor goes... once you have your grounds right anyway.

For tweak #1 - The C4 optional cap just doesn't do anything for me... I'd say leave it off.

rj

[RJ Guitars]

Rocket Tweak #2

If you are familiar with the VOX tonestack used on the Rocket, you know that when you max out the bass control the mid's take a huge dive. If you evaluate the schematic, it's no wonder... you are shorting the mids to ground as the value of the pot becomes less than the 10K between the wiper and the third lug.

I posted on this a while back... https://tubeamparchive.com/viewtopic.php?t=6332

It seems there is a very easy fix... let me know if anybody else has seen this and has the same result. Remove one end of the resistor from the third leg of the pot and connect it to ground. This leaves one end of the mid resistor connected to the wiper on the bass pot and the other one connected directly to ground. Viola... exact same behavior in the lower levels but doesn't go funky when you max out the bass control.

I changed this on both of my Rockets and it works excellent!

I changed the H1d layout to reflect this change... by the way this looks a whole like a Fender tonestack.

rj

[Blindog]

I don't think it really shines so much as a lead amp though....

Don't tell Brian May Yeah, I know he uses AC30's, but try this amp with a pedal and I think you will like!

I recently gigged with my Rocket. I had the volume set at 12:00 (sound guy was telling me to turn down!) Hooked up to a closed back 2X12 cab with Vintage 30's. I had my OCD set up for a clean boost and it really sang for solos. I'm going to try it out with a BBE Freq Boost with the bass and treble controls flat to approximate the normal channel of an AC30 (like Brian uses) and see how she sounds.

I had an AC30TBX (one of the last made in England) and I think that this amp greatly outshines it.

Mark

[dave g]

There's a few things that I have done to my Rocket lately that have really improved it and made it a far better amp for my playing style. A few of them may not be 100% kosher, but I prefer the sound of the amp with these mods:

-I threw a DPDT switch on the front panel that puts a 500p in parallel with the first coupling cap to give 1n, as well as putting a 500p in parallel with the 50p treble cap. The switch essentially takes you from a Vox voicing to a Marshall voicing.

-I reduced the four .047s in the PI to .022. I really love the added tightness.

-I changed the PI cathode resistor to 820R and the tail resistor to 10k. I hate the cold biased Vox PI that all EL84 amps seem to use - fizz city! I also changed the PI plates to 82k/100k...so I guess you could say the PI is pretty much Marshall spec.

-I also use both halves of V1 in parallel with a 100k shared plate and 1.5k shared cathode. V2a is then the 2nd gain stage and V2b the CF.

I did most of these changes with the intention of making my Rocket a better lead amp - the sound I had in mind was Dick Wagner/Steve Hunter on Rock and Roll Animal. I usually run the volume flat out with the cut at 1:00 and the treble and bass both at noon (with the toggle switch in the marshall position), and use the guitar's volume knob to do the clean to mean thing.

FWIW, I'm using a closed back 4x12 with greenbacks.

[rfgordon]

On my Rocket combo, I added a mid control. I also used both sides of V1 in parallel. It turned out to be a truly marvelous amp. The guy who bought it, out in Montana, just loves it. I didn't wanna part with it, but you know how it goes.

The color-shifting vinyl I used on the cab was left over from a harp amp build where the customer picked out the Skintex Chroma vinyl ($69.95 per yard--yikes!!). As you move around the amp it shifts from green to goldish to purple. Looks absolutely killer under stage lights.

[RJ Guitars]

I don't think it really shines so much as a lead amp though....

Don't tell Brian May Yeah, I know he uses AC30's, but try this amp with a pedal and I think you will like!

I recently gigged with my Rocket. I had the volume set at 12:00 (sound guy was telling me to turn down!) Hooked up to a closed back 2X12 cab with Vintage 30's. I had my OCD set up for a clean boost and it really sang for solos. I'm going to try it out with a BBE Freq Boost with the bass and treble controls flat to approximate the normal channel of an AC30 (like Brian uses) and see how she sounds.

I had an AC30TBX (one of the last made in England) and I think that this amp greatly outshines it.

Mark

Mark, Correct you are... Brian May has done O.K. for himself with the AC-30. I agree, if you get a pedal in there you can extend the services of this amp.... but don't tell my wife, I've got her convinced that I "need" one more amp.

Nothing shy and quiet about these amps... I am always getting the "can you turn that thing down" from the singers.

I'm using an open back with 2-10's and I really like what it does. I've played it through an open back with 2-12's (vintage 30's) and I really liked that also. With my closed back 2-12 cab it flabs out a bit when I crank it, but I think that it is the speakers.

rj

[RJ Guitars]

On my Rocket combo, I added a mid control. I also used both sides of V1 in parallel. It turned out to be a truly marvelous amp. The guy who bought it, out in Montana, just loves it. I didn't wanna part with it, but you know how it goes.

The color-shifting vinyl I used on the cab was left over from a harp amp build where the customer picked out the Skintex Chroma vinyl ($69.95 per yard--yikes!!). As you move around the amp it shifts from green to goldish to purple. Looks absolutely killer under stage lights.

Cool Amp - I think it is the simplicity of them that makes them so cool. Did you ever compare the 2 tube and 4 tube versions? I'm curious what you used for iron and what your voltages are.

You have some great data points with V1 parallel option and the mid control. The mid control would be a good tweak for you to post if you are so inclined.

I'd kinda like to chart a bunch of these and see what the voltage profiles look like... maybe Allyn will bless us with the voltages from the real Rocket?? Maybe please sir?

rj

[dansamp]

Rocket Tweak #2

If you are familiar with the VOX tonestack used on the Rocket, you know that when you max out the bass control the mid's take a huge dive. If you evaluate the schematic, it's no wonder... you are shorting the mids to ground as the value of the pot becomes less than the 10K between the wiper and the third lug.

I posted on this a while back... https://tubeamparchive.com/viewtopic.php?t=6332

It seems there is a very easy fix... let me know if anybody else has seen this and has the same result. Remove one end of the resistor from the third leg of the pot and connect it to ground. This leaves one end of the mid resistor connected to the wiper on the bass pot and the other one connected directly to ground. Viola... exact same behavior in the lower levels but doesn't go funky when you max out the bass control.

I changed this on both of my Rockets and it works excellent!

I changed the H1d layout to reflect this change... by the way this looks a whole like a Fender tonestack.

rj

RJ
I had thought about putting toggle switch for this set up maybe between the bass and cut knob or next to the cut knob
that way you could have a "vintage/modern" switch
vintage being the "incorrect" Vox/Gibson circuit ungrounded
and the modern being the "correct" Fender style tone stack grounded.


Dan..............

[Normster]

I guess it's a little more than a mod, but I recently added reverb to a rocket build and like it a lot. I think it helps set the rhythm guitar back in the mix a little better.

Here's a clip with the volume backed way off for some nice clean tone.
http://www.bad-domain/MP3/SpaceCadetTeleClean.mp3

[rfgordon]

For my Rocket, I used PT/OT from Matt at Musical Power Supplies. The choke is a generic "small Fender" type. The power tubes are a pair of 6V6s, rather than EL84s. I used Matt's PT325, which, if I recall correctly, put about 390 VDC on the 6V6 plates with an 5Y3 recto. V1 plates were around 185 or so, I think, with a PRP 100k plate resistor.

When cranked, this thing had the most amazing crunch!

[rfgordon]

Here's a clip of the Rocket V6 with the guitar volume rolled back, then full on, then back down again at the end. I think the amp gain was around 2 o'clock.

[RJ Guitars]

I guess it's a little more than a mod, but I recently added reverb to a rocket build and like it a lot. I think it helps set the rhythm guitar back in the mix a little better.

Here's a clip with the volume backed way off for some nice clean tone.
http://www.bad-domain/MP3/SpaceCadetTeleClean.mp3

Normster that is a great looking Rocket and the clips are excellent. Can you share the Reverb circuit and details with us?

Also, your power tranny looks like a Heyboer standard, let me know if I'm wrong. I'm curious about the Output tranny. I found the Heyboer TW5200 (5.2K winding) to be absolutely excellent in this build, but I am curious what other folks are using.

Great job and always nice to see and hear your work.

rj

[RJ Guitars]

There's a few things that I have done to my Rocket lately that have really improved it and made it a far better amp for my playing style. A few of them may not be 100% kosher, but I prefer the sound of the amp with these mods:

-I threw a DPDT switch on the front panel that puts a 500p in parallel with the first coupling cap to give 1n, as well as putting a 500p in parallel with the 50p treble cap. The switch essentially takes you from a Vox voicing to a Marshall voicing.

-I reduced the four .047s in the PI to .022. I really love the added tightness.

-I changed the PI cathode resistor to 820R and the tail resistor to 10k. I hate the cold biased Vox PI that all EL84 amps seem to use - fizz city! I also changed the PI plates to 82k/100k...so I guess you could say the PI is pretty much Marshall spec.

-I also use both halves of V1 in parallel with a 100k shared plate and 1.5k shared cathode. V2a is then the 2nd gain stage and V2b the CF.

I did most of these changes with the intention of making my Rocket a better lead amp - the sound I had in mind was Dick Wagner/Steve Hunter on Rock and Roll Animal. I usually run the volume flat out with the cut at 1:00 and the treble and bass both at noon (with the toggle switch in the marshall position), and use the guitar's volume knob to do the clean to mean thing.

FWIW, I'm using a closed back 4x12 with greenbacks.

Dave,

You've got a hand full of mods for us to consider there... sounds like you've got it dialed in pretty well to suit yourself. Has anybody else pushed a Rocket a bit to make it more of a lead amp?

I'm, really curious about putting the V1 in parallel and what that does for tone and gain.

Also, I'm curious if anybody has compared tone with a gain stage and the cathode follower on V2 as opposed to both gain stages on V1 and the cathode follower all by itself. I guess I need to see how Marshall and Fender handled that. It just seems that it's a waste not use that extra gain stage somewhere...

I've got some more tweaks that I'll post later when I can get a couple pictures to go with them...

rj

[RJ Guitars]

Here is one that I added to my VOX powered Rocket. I used all VOX iron for this build. It does sound a little different than the Heyboer unit, although not hugely different.

Maybe Dana will chip in if you have any questions about the VVR. It's a cool addition and gives you a lot of diversity for under $50. I've found that I kinda loose some of sparkle from the amp when I get down below 30%, but that is also getting down to where the speakers are not working very hard.

A good unit and pretty simple to install. I used the hole for the Standby switch to bring the control pot out the front. I don't have a standby switch anymore but I don't think I need it since I am using a GZ34 rectifier tube.

I really need to put some miles on this unit to understand and evaluate it better, but it's definitely a great sounding amp!

thanks Dana!

rj

[Normster]

RJ,
The reverb circuit is lifted from the Matchless Lightning Reverb, although I'm only driving the return with one triode. BTW, take a close look at the schematic and you'll see that it's very close to a Rocket and has a parallel triode driving the second gain stage and cathode follower.

Trannys are standard Moose fare using the 5k tap on the OPT.