New Rockets, one with a twist..

[Cliff Schecht]

I built these two Rockets back to back. One of them is about as standard as you can get for a Rocket (well, as standard as I would get ) and the second one is crammed in a much smaller chassis with a 6AQ5 output section. Both of them use gold turrets (hard to tell in the pics after soldering) but I made the board for the second one out of some clipboard material I found.

The more accurate Rocket uses my "standard" PIO/polystyrene cap combo with Stancor iron. The PT I scored from Dynaman and the output transformer (Stancor A-3800) I had lying around. Only thing I changed was 0.033uF caps for the tonestack caps (for now) because I didn't have any high voltage 0.022uF guys sitting around at the time. Master volume is a dual 500k AB pot with 1.6M resistors strapped which give a nice transparency at higher volumes and a nice natural sweep when attenuating. This was my first Rocket build and I must say, it's a truly great sounding amp. I can definitely appreciate the lower gain (although it does get after it when cranked) and LOVE the cleans through both my 4x12 Vox cheapo cab and my EV SRO loaded 1x12 ported cab. I was actually building this for a friend but this is one of those builds that I don't want to let go. Instead I've gotten another A-3800 off of fleabay and will build him an amp when I find a suitable PT and chassis. This amp loves Bugle Boys in the preamp and good ol' American EL84's in the output section.

The second Rocket came about from wanting to do a 4x6V6 Rocket but not having appropriate iron to do so. What I did have was an old PT from a reel-to-reel player (250V @ 250mA and no CT) and pretty much everything else I would need for the build. Only catch is the PT doesn't have enough current on the 5V tap so I opted for just a bridge rectifier and a Zener to drop the B+ down to about 275V as the 6AQ5 datasheet calls for. The output transformer is a NOS Stancor A-3851, including the unused 10% inverse feedback windings. Since this transformer might not stay in this build (it's really for 6L6's), I left all of the leads at their super long length and tied them back as needed. I ended up with a 100 Ohm cathode resistor which put each tube at a hair over 40mA a piece, which was better than the 50 Ohm resistor both tonewise and for my B+ (which was dropped TOO much with the 50 Ohm resistor). As far as sound goes, I absolutely love it! Maybe even more so than my "real" Rocket clone. The PI and output stage seem to clip about the same as the real Rocket and the gain feels about the same but the amp itself is a bit less bright and looser in the lower end, which I like quite a bit. It's also a "quick" amp, very responsive to playing style and cleans up beautifully with slight volume knob and pick attack adjustments. The other funny thing I noticed was that this amp is noticeably quieter than my other Rocket. I also love that a set of 6AQ5's costs about 1/4 what a cheap set of EL84's cost and they're all GE/Sylvania/RCA brand NOS! But I had these on hand and so my actual build cost was all of $10 for a few sockets! For preamp tubes I'm using a mix of RCA and Sylvania to get a more "American" feel from this amp. The other thing you guys might notice about this build is that I did it backwards. This was not intentional but I was using my first Rocket build flipped upside down as a guide and forgot to compensate for this! All worked out fine in the end but I definitely did some headscratching at first trying to figure out what to do after I cut out the power transformer mount on the wrong side of the chassis..



Here's some pics for now:

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[Teleguy61]

Cool!

[M Fowler]

Nice pair of amps Cliff and your enjoying them that's even better.

[Jackie Treehorn]

Nice amps! I like the Dual AB pots and PIO caps.

What's the story on that Stancor OT? It has a 10% tap for cathode feedback? Did you hook that up?

[amplifiednation]

very nicely done!! I like the two versions. i had an old gibson with the 6AQ5s and they were pretty cool tubes and definately on the cheap. i had a nice pair of NOS and one of my dogs got a hold of the box the tube was in and broke it.

I'm nearing the end of my rocket build (first build!) and it's been a lot of fun and a huge learning experience. I added reverb and plan to also add the boost and possibly the VVR.

I can't wait to hear the amp...right now I'm just hoping that it works!

[ChrisM]

Is that an LED on the PI socket?

[Cliff Schecht]

Is that an LED on the PI socket?

I hope not!

Jackie that Stancor iron was one of a pair that I found and had sitting around. Great for Fender builds, I have the other in my tweed Bassman build and before that it was in my octal tweed Deluxe build. The iron has tertiary 10% inverse feedback windings (i.e. an independent primary side winding) that I've never put to use in an amp before. TBH I just don't see the need for them when I'm going for relatively vintage-correct builds, but I'll probably pull these one day for use in a hifi build and replace the iron with something just as appropriate. I've seen schematics that use the 10% feedback winding through one stage behind the phase inverter but I don't know of a single guitar amp that would benefit from more linearization like this (maybe for bass or jazz?).

I took this in to the local vintage amp guru in town and we put the 6AQ5 Rocket up against an Orange AD30 and a few other amps (including a SUPER clean brown Princeton non-reverb). I'm really digging the sound through a closed and open back sound, it's definitely got that wide-open no negative feedback sound that I dig in my SE designs and gets a great crunch when you crank it. I love the tonestack setup of the Rocket and once you find the sweet spot it has a great sound. Pretty much what you would expect with a 4x6V6 Rocket, a bit sweeter in the mids and more smooth in the high end.

The one thing I noticed was that on the lower notes on the g-string even with the amp set clean the first few notes seem to always want to distort, even if it's just a bit. I think this has to do with the second cathode being bypassed with a 22uF cap and the 68k cathode follower resistor. I'm going to pull out the 22 uF guy and drop the 68k to 100k to try to knock down the gain and eliminate this little g-string buzz issue.

[Cliff Schecht]

I think taking out the second stage 22uF cap helped settle the 6AQ5 amp down a bit. The buzziness on the g string is gone for the most part, or at least is less pronounced, but I'm not sure how to get rid of this completely. I'm going to change my cathode follower resistor to 56k and see what this does.

Also I might be ripping the A-3851 out of this in favor of using an A-3800 like in my other Rocket build. I think the 3851 would be better suited for the tweed Twin I'm planning next.