The Rocket build thus far

Mark · Post by **Mark** » Mon Oct 28, 2013 3:16 am

I was always in awe of Allyn Meyer's Rocket build. It is probably the best Rocket build I've ever seen.

https://tubeamparchive.com/viewtopic.ph ... ght=rocket

I've wanted a Rocket for a while and I thought I'd use Allyn's build as a template to build my own amp. Here are a few pictures of the amp build.

It isn't entirely the same as Allyn's amp as the chassis I got from RJ isn't the same as Allyn's (Liverpool chassis with rectifier hole added). The issues I've had with the chassis were related to using new smaller caps rather than the larger vintage types. So problems of my own making rather than issues with RJ's chassis.

The issued started with using a Classic Tone power transformer which has a different mounting hole locations to RJ's chassis. This then put the mounting screws near the positive leads of the filter caps. Here are the photo's.

http://i149.photobucket.com/albums/s69/ ... 95ed7a.jpg
http://i149.photobucket.com/albums/s69/ ... 0f81c3.jpg
http://i149.photobucket.com/albums/s69/ ... e6e841.jpg
http://i149.photobucket.com/albums/s69/ ... d84f23.jpg
http://i149.photobucket.com/albums/s69/ ... 0d8b0f.jpg

Here is the thread with pictures of JM's Rocket, I still like Allyn's Rocket better than JM's Rocket, it's a cleaner build and the inclusion of the filament transformer and Norlin switch didn't impress me.

https://tubeamparchive.com/viewtopic.ph ... 307#274307

Please give me any feedback that you think is helpful.

Firestorm · Post by **Firestorm** » Mon Oct 28, 2013 3:44 am

Can't really tell how close that tranny bolt is to the anode of the middle bottom cap. There's a huge potential there so maybe some insulation is in order.

Mark · Post by **Mark** » Mon Oct 28, 2013 5:50 am

Thanks for the feedback Firestorm.

There is about 5mm from the positive terminal of the cap to the nut. DC shouldn't be able to jump to earth but why would you risk it anyway. I will be elevating the caps up off the chassis.

Had I not used the Classic Tone iron it wouldn't have been an issue.

I mentioned moving the rectifier tube and moving the choke a little and RJ was great, he took my advice in the positive spirit in which it was intended.

Hopefully future builders will benefit from my experience. I do think I should have asked RJ about his Rocket power supply board it might have been a good idea.

The pictures aren't great they are more for my reference.

M Fowler · Post by **M Fowler** » Mon Oct 28, 2013 12:58 pm

With situations like that I run the mounting bolt from the inside to outside nut on top to give me ample clearance .

Mark · Post by **Mark** » Mon Oct 28, 2013 8:40 pm

Thanks for the feedback Mark that is a good idea.

I would expect to get between 7 or 8mm of clearance after that change, I'm wondering what clearance would acceptable?

M Fowler · Post by **M Fowler** » Tue Oct 29, 2013 1:45 am

Based on your photo above once the bolt is reversed there should be plenty of clearance. You could put a short piece of shrink tubing or spaghetti over the lead for safety measures.

Firestorm · Post by **Firestorm** » Tue Oct 29, 2013 3:00 am

It's ugly, but there is that liquid electric tape stuff. I did a triode/pentode switch on a 100W Marshall where the size of the signal swing (7-800V) was enough to arc between the switch terminals. Two coats of the black goop fixed it. (But then we said, this triode thing sucks anyway, and took it out).

Mark · Post by **Mark** » Tue Oct 29, 2013 7:50 am

I flipped the bolt around and it looks much better. I shouldn't have a problem with it now. I'll be glad to hear this thing make a sound.

I still think the rectifier tube is about 10mm too close to the filter caps, but there's not much I can do about that.

Mark · Post by **Mark** » Wed Oct 30, 2013 1:23 am

Turning the screw around helped but here are other issues.

http://i149.photobucket.com/albums/s69/ ... ce59fa.jpg

http://i149.photobucket.com/albums/s69/ ... fc10b4.jpg

http://i149.photobucket.com/albums/s69/ ... 9f0992.jpg

The added height helps clear the rectifier tube which is a bonus. I think RJ needs to look at Allyn's Rocket pictures, the current position does make things more difficult than they need to be, and I'm sure RJ does look to improve his product.

Edit: I swapped the screw back over and inverted the other screw (near the front panel of the amp) I found this gave me a lot more room to move the caps back and avoid being too close to the rectifier.

Mark · Post by **Mark** » Sat Nov 16, 2013 12:28 am

Bob S · Post by **Bob S** » Sat Nov 16, 2013 1:00 am

First off - that looks great Mark.
As clean a build as I've ever seen - seriously.
I'd check the wall supply earth/ground before you touch anything.
Switch off anything close by with a microprocessor.
Also any lights that don't have a regular filament.
Very impressive !

jelle · Post by **jelle** » Sat Nov 16, 2013 2:03 am

Make the sure the V1A coupler is a CDE brand 500pF cap. The other brand from india has caused me issues before.

And like I said before, AWESOME!!!!

Mark · Post by **Mark** » Sat Nov 16, 2013 6:42 am

Bob and Jelle thanks for the kind words, I've seen some beautiful work done at this forum and it is good to know my work is worthy of this forum.

Thanks for the tip on the cap Jelle and I'll give that a try Bob, there is so much junk in the modern-ish house (dimmers for example are just made to create noise and occasionally dim the lights).

EDIT: The yellow CDM cap was a dud, I bought this as I thought I lost the one RJ supplied (I later used it and it works fine.) I lifted the cap and it had 2.4VDC on it, not good.

I'm still working through the other issues.

EDIT 2:I had a bit of a look at the noise tonight. I think it is an actual noise and not hum. I removed V2 which is the follower that drives the tone controls and the noise it still there. I measured the amplitude of the noise at the output of the amp and it measures 33mV, I tried to measure it at the input to the PI and the leads pickup even more noise.

I thought I'd try and ground the coupling cap (220K side) prior to the PI stage, it worked like a charm the noise is gone, I try grounding the side of the 220K which joins up to the wiper of the treble control and the noise is a little quieter but still there. I built a prototype Rocket years ago and it had this issue, no matter what I did, I couldn't get rid of the noise, any thoughts?

https://tubeamparchive.com/viewtopic.ph ... ight=noise

The noise still exists if I remove any input to the PI, and it looks like this.

http://i149.photobucket.com/albums/s69/ ... 6e2479.jpg
http://i149.photobucket.com/albums/s69/ ... cd0015.jpg

I think the signal at the grid is about 12mV in amplitude, I even turned on my 18 watter to see if it has this noise, it's reasonable quiet with no noise and little hiss.

CoffeeTones · Post by **CoffeeTones** » Tue Dec 10, 2013 6:26 am

Mark, try moving the PI ground to the top of the stage two, 1k5 cathode resistor. In fact, I'd ground the PI, stage one and two cathodes, plus the cathode follower's 100k load resistor all in a line to the same point.

I had this same issue before and this resolved it.

Mark · Post by **Mark** » Tue Dec 10, 2013 9:53 am

Thanks CT. I'll give that a try.

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