Building a Rocket - Layout Check for group build

[Fischerman]

FWIW, I finished it up and fired it up late last night and everything worked. My AC voltage is a little high...122vac-124vac or so. B+ voltages were 312vdc for the OT CT and 300vdc for the screens. The plates were at 303vdc, screens at 297vdc (470ohm screen grid resistors) and the cathodes were at ~9.5vdc (50ohm shared cathode R with 200uF cap). That all seems about right...it's a pretty hot bias. Trannies did not get hot.

Played it at low volume for a bit. Sounded good but I didn't play it for long and not at any volume (except for a second...it got loud is about all I can tell you ).

[Lonely Raven]

Awesome, Matt!

Tell us what you think when you get some CRANK on!

I'm still waiting on my chassis. RJ's and mine were the last two put together...no hurry since I don't even have a work bench setup, nor parts on hand to build her up.

Have we settled on the Layout? I'm totally a paint by numbers kit builder, so I absolutely need the layout to help me along. Though I've built about a half dozen amps without any sort of directions or guidance, I've always had a good layout and/or photos to follow.

[Fischerman]

Eric,
My layout is my own and not really like a real Rocket so my layout would probably just cause confusion. But I'll post pics soon. I still haven't received my faceplate and I was hoping to at least have that installed before I post pics. But gutshots are the same either way.

And FWIW, crunching my numbers from above (restated here):
Plates = 303vdc
Cathodes = 9.5vdc
Screen supply = 300vdc
Some screens were 296 some were 297, so I'll take 296.5 as an average
Shared cathode resistor = 50ohm
Seperate screen grid resistors = 470ohm

300vdc - 296.5vdc = 3.5vdc
3.5v / 470ohm = .00745 A or 7.45mA per screen
296.5v - 9.5v = 287v
.00745 * 287 = 2.14W per screen

9.5v / 50ohm = .19A = 190mA
190mA / 4 = 47.5mA
47.5mA - 7.45mA = 40.05mA
303v - 9.5v = 293.5v
40.05 * 293.5 = 11.75W per plate

All seem reasonable. Even though I'm using 470ohm screen grid resistors the screens are slightly over the max dissipation (data sheet says 2W) but the plates are slightly under the max dissipation (data sheet says 12W). This is not a matched set BTW...all I had on hand. Will be curious to see what the numbers are for a 'stock' arrangement.

Is this work day over yet?!?!?

[guitarsnguns04]

I will be joining in here shortly as well. My chassis is coming in with yours lonelyraven. I have been keeping a close eye on the progress though. I cant wait to get going. I have to get the rest of my parts as well but I have a bunch from my express build left over. I ordered extra everything for stock. I am looking forward to your pics fischerman!

[RJ Guitars]

Forum,

I've just been presented a question about wire type and size. I kinda work in the Rocket Science Business, literally, no pun intended. In non-amp Rocket Science circles we don't believe that electrons are not smart enough to sound better when they travel through a single solid wire or several smaller strands combined together.... but then again we don't build guitar amps where I work at my day job.

I may not be the right person to answer because I am always going to use quality stranded wire with teflon insulation. I like 20 gauge unless something is going to carry some extra current. I've found that as I build more amps I am not as tempted to overgauge the wire, it makes building an amp a lot messier and jams up turrets and eyelets and also requires more heat to solder it. The colors are always selected by what I have available, choosing my favorites first then use the others as I go. Here is a general idea of how it usually ends up.

Red - B+
AC - Black and White
Ground - Green
Heaters - Yellow and Orange
Signal - Blue

This has never been entirely hard and fast for me, but helps me keep things sorted out.

Since my first ODS build I always keep the heater wires polarized so that requires two colors for me to keep track of it.



I know there is some Trainwreck mojo about solid wire and there is some good historical results among the veteran Trainwreck builders... would you share that with us?

Thanks

rj

[angelodp]

jeepers - Fisch - what does the baby sound like.... we are all on tenter- hooks.

lol Ange

[tubetek]

Howdy, RJ-
In my experience, the solid-core is stiff enough to stay where you put it; makes chopsticking to "tune" the amp a lot easier. I also use PTFE (teflon) insulated wire whenever possible. (Just be sure you have strippers that will handle it)
Tom

[tubetek]

Duplicate Post!

[Fischerman]

I'm lazy and I have cloth-covered wire on-hand so that's what I used for the preamp and heaters. Actually the fat green cloth-covered stuff I use for the heaters isn't any easier than regular...maybe more of a PITA because you have to strip it like regular wire but then you also have keep the cloth strands in control. But it looks kinda nice. The cloth covered stuff I use for the preamp is just so easy to use...no stripping...just cut it clean and pull it back...and it's solid strand so it stays where you put it. I used PVC covered wire for most of the power supply/AC stuff. I use a color scheme but it varies...you'll be able to see it in the pics. I don't use different colors for the heaters simply because I only have that fat green stuff in one color...a little dab with a Sharpie at each end works wonders.

Took pics but it was late and didn't upload them, hopefully tonight. I was busy with other stuff but I did get to play it a bit yesterday. It does the barely-breaking-up-twangy-thing great. It transitions into OD smoothly, the controls have a great range too. FWIW, I used a linear 1M for the Treble and a audio (log) 1M for the Bass control ('stock' values are linear 1M for both). The Bass control has a nice smooth taper to it...no jumps...I would be interested to hear how the taper is for those that use the stock linear 1M for the Bass control. Cut control works really well too...I don't see any glaring need to adjust the cap value. Oh yea...the bright switch doesn't do as much as I expected...it's a 3-way switch with 47pF and 100pF and you can barely tell the 47pF is on or not. And I think I prefer it with no bright cap...the bright cap just makes the high end a bit more 'brittle'. Overall it has a very nice, balanced tone...it's not too bassy or trebley...and even if you dial in too much bass or too much treble it still sounds good. I was using a 4x12 basketweave-type cab with 2 each Scumback H75s and 2 each Celestion G12H30 (70th Anni RI...not Heritage). And this is with 2 new matched EH power tubes, 1 old Sovtek EL84M, and one old JJ...so my power tubes are not matched by any stretch...and the preamp tubes are just what I grabbed when I fired it up.

Haven't played it enough yet but first impression is...me like!

Oh yea...I didn't know what mains fuse value to use and I originally tried 2 amp slo-blo and it blew. Apparently the Vox use 4 amp slo-blo for 120vac amps so I stuck a 4 amp slo-blo in there and it hasn't blown. I'm using a 0.5 amp fast-act for the HT fuse and it has not blown.

[Allynmey]

Fischerman, congrats on the build. Here are a couple of things to try...

100 Ohm screens (the way KF built them).
NOS Russian military EL84's from the early '80's (KF again).

If you like more girth in the sound, use the higher voltage tap and a 68 Ohm Cathode resistor. It takes away a slight amount of jangle but, adds midrange "girth" (courtesy of a Rocket owner).

Allyn

[Fischerman]

Hi Allyn, thanks for the suggestions. Why 100ohm screen grid resistors? I know that's what KF copied from the Vox AC30...but I've had several people tell me that 470ohm is easier on the tubes and they didn't notice any tonal degradation. Some suggested that be the only thing I change.

The Russian military EL84 is what I usually use but I just haven't bought a matched quad for this amp yet.

I don't see any need to change anything yet (I'm sure that will change after I've played it more!)...it sounds really good. It has a very jangly, bouncy tone/feel that's very fun to play and that's with the only four EL84s I could cobble together (my Velocette blew the screens in the other JJ and EL84M because that stupid connector for the OT lost a plate connection = all current through the screen = dead tube). I'm anxious to hear it with a good set of tubes.

[Lonely Raven]

NOS Russian military EL84's from the early '80's (KF again).

Allyn

I just got a set of these from Sargent Overdrive. He highly recommended them so I bought extras for my 18 watt (that I need to figure out how to voice as I'm not happy with it).

[Allynmey]

Sarge is the best! and has those nice Saratovs for sale.

[RJ Guitars]

Fisch,

Can you share with us about the layout you chose. Did you go with the Mark Abbott layout or anything like the ones proposed in the group build effort?

I can't wait to see pictures and hear some clips.

Thanks,

rj

[guitarsnguns04]

I would love to see it as well...I would love to hear it also...lol..Any chance on pics and clips? I cant wait to join in on the fun!