Rocket mods

[Mark]

I thought I'd share mods that I did to my Rocket. One of the issues a Rocket has is the pre-amp plate of the first triode operates at a relatively low voltage, this causes DC to get onto the grid and thus onto the volume pot resulting in a scratchy guitar pot when adjusting the volume. The fix is to either block the DC with a cap or to raise the DC voltage to the plate.

IMG_1400.JPG

I wanted to know the current through each EL-84 so I added 1 ohm 1% resistors to the circuit. I find them really handy knowing what each valve is doing.

IMG_1401.JPG

Given that the cathode follower does operate under difficult circumstances. I decided to implement Merlin Blenecowes mod to prevent arc over which would damage an otherwise good valve.

I also implemented Ken Fishers voicing mod.

IMG_1402.JPG

The voicing mod is fairly subtle, it is basically a slight mid cut which sound better for humbuckers.

This sort of thing has been discussed before but as there has been Rockets discussed lately, I thought I'd mention it.

[joeboo88]

Hi Mark. Good info.
My rocket also had low voltage at V1. Aaron (Xtian) helped me out with this, like the first picture ( scratchy pots)

Anyways thanks for the info

[Mark]

The Marshall style power supply is the issue. The Vox AC-30 uses a parallel power supply which I assume is a bit noisier as it hasn't the series Pi filters the Marshall style power supply has, but the Vox power supply delivers higher voltages. The Dr Z version of the Rocket uses the Vox style power supply.

[Dmessick]

The details in these pictures are great!
What is the purpose the diode/resistor on pins 3 and 4 of the third picture? I have not seen that before.

[Mark]

I got the mod from Merlin Blenecowe on his valve wizard site. About half way down the page it describes the purpose of the diode and resistor. It protects the cathode follower on start up. With the high cost of NOS and in my case ANOS valves, I didn't want to be going through 12AX7's. The beauty of the Rocket is you can even use valves like a 12AT7.

http://www.valvewizard.co.uk/dccf.html

[Roe]

Whats the voicing mod?

[Mark]

I saw the voicing mod in a real Rocket. Ken Fischer installed it. It puts a 22uF cap across the 1.5K (R5) and put a 220K resistor to ground to form a voltage divider with the 220K (R10) going to the P.I. stage.

https://ampgarage.com/forum/download/file.php?id=8003

[norburybrook]

Mark,

When I added a VVR to my Rocket/Z Wreck I had to install a cap to stop DC and scratchy volume control


I now have the rocket/Z Wreck differences on a switch so I can flip between them, one of them has more gain, I can't remember which though.

I use Russian Military EL84's and they've been very good.


M

[Mark]

I'd like to see how you switch between a Z Wreck and a Rocket. I'm not sure which amp would have more gain. My Rocket does decent overdriven tones, but I really like it's clean tones best. It is quite a loud amp though, not a bedroom amp.

I have VVR to install in an amp, but I don't know which amp it would work best in. The Express was my first choice for VVR, but dropping pre-amp voltages effects the tone of the amp.

[Dmessick]

I just added this voicing mod this evening and I think I will like having the option to change the character of the amp a little bit. I previously had the bypass cap on a switch so I just added the voltage divider to the same switch. I know there are a few more differences between the Rocket and Z-Wreck than just these two components but I think I will find it more useful than having just bypass cap switched as a boost.

I'm not sure if I can pick a favorite setting yet, I don't dislike either of them. My initial impression is the "Z" setting is a little tighter and might work better in the context of a band with 1 or two other guitar players/keys.

I should also note that I have a PPIMV in this amp and have only been able to play it at about 50%. I'm not sure yet how these different settings will sound at full volume.

[M Fowler]

The Zwreck has a different dropping string then the Rocket.

Early versions of the Zwreck also had lower filtering 8uf/450 B+1 and 2.

My Zwreck has a darker character to it which could be the Russian tubes and Edcor transformers.

Mark

[Mark]

Though I would show pics of the finished amp. Still going strong and getting plenty of love.

CEBF1F3C-38C7-4ED5-9391-A2EB5154EF93.jpeg

CEBF1F3C-38C7-4ED5-9391-A2EB5154EF93.jpeg

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[Colossal]

That's a beauty, Mark. A very clean build. What speakers are you running in that 2x12 and open or closed?

Cheers

[Mark]

That's a beauty, Mark. A very clean build. What speakers are you running in that 2x12 and open or closed?

Cheers

Thanks for your kind words.

I’m still working out the speaker situation. I have been using my Marshall 18 watter as a speaker box. It has a Blue and a H30 in it.

In the pic the amp is sitting on a 2X12” cab with Mojotone Greyhounds in it. It’s Barry Marie’s cab and he finds they sound good with any amp.

I had heard good things about a Jensen Neo speaker, but I haven’t made any decisions yet.

https://ampgarage.com/forum/viewtopic.php?f=1&t=36198

[gktamps]

Beautiful amp, Mark!
Long ago I also adopted Merlin's cathode follower protection mod - use it on all my builds, and documented them here on AG.
I've also incorporated a series of different tone shaping mods, as I thin the Rocket really manages a pretty wide range of parameters well. Plenty of versatility available with the base circuit, and mods don't have to change the character of the amp too much if not desired.
I also had VVR on one Rocket that required the input cap. After removing the VVR I kept the cap - it does help.