my 18 watt rocket-ish build

[wsaraceni]

so this has been a fun project. i've had an express chassis that i gutted since it was a total mess and i wanted to start over. i've gone through 4 different ideas before i found one i was happy with. i thought i'd share some of my work so far and maybe get some comments or recommendations.

to start, i've built an ax84 p1 which i have since gutted, i dont like single ended amps with full tone stacks, it seems a waste to me.

i've built the express, and while i like the express, it wasnt ever 100%. it was very noisy and just too messy. not a great idea for a 2nd amp build.

i've built an 18 watt lite iib out of a fender blues jr. i gutted that chassis because i want to build a 5e3 in it. but i used the iron for that to come up with this. all the posts here have been a big help

so i call this a rocket-ish build, but it's obviously closer to the ac30/drz stuff. i even thought i'd give his layout a try.

i've started with the express chassis with a rattle can finish on the outside and sandblasted the whole thing. komet style ceramic tube sockets and PEC pots

[img764]http://img.photobucket.com/albums/v217/ ... a29586.jpg[/img]

[img764]http://img.photobucket.com/albums/v217/ ... 3c36bc.jpg[/img]

blank board material from turretboards.com

mental note for next build. dont put anything that gets screwed down beneath the overhang of the chassis. the power supply board is very hard to get the screws on

[wsaraceni]

i have not having a detachable power cord. but the hole was too big to cover with a standard IEC socket. so i got one with a fuse attached

[img764]http://img.photobucket.com/albums/v217/ ... f1f2ef.jpg[/img]

this allowed me to add a 2nd HT fuse. not sure if it's needed, but why not.

then i installed the PT. for those that have followed my thread on the headphone trick issue, i wish i waited longer before doing this. but here is the wire route i've ended up in.

[img:764:1024]http://img.photobucket.com/albums/v217/ ... 6a521e.jpg[/img]

just waiting for the heater wiring to finish that up. i have since shortened the yellow and red wires but dont have a picture of that

[wsaraceni]

since i'm waiting for heater wire i've decided to start to do my layout. figured it would be easiest just drawing it right on the board

[img:764:1024]http://img.photobucket.com/albums/v217/ ... cdff4a.jpg[/img]

i also finally found a trnasformer layout that worked and mounted them up.

[img:764:1024]http://img.photobucket.com/albums/v217/ ... a39495.jpg[/img]

[wsaraceni]

here you can see the B+ wiring as well as the blue and brown wires. I'm thinking it might be better, after the heater wiring is done, to run those around the backside of the tubes, just in front of the OT wires. what do you think?

[img:764:1024]http://img.photobucket.com/albums/v217/ ... 8b31f7.jpg[/img]



still waiting for the right heater wiring so i figured i'd start with the preamp board.

[img764]http://img.photobucket.com/albums/v217/ ... 933b9a.jpg[/img]

[img764]http://img.photobucket.com/albums/v217/ ... f9d3df.jpg[/img]

[wsaraceni]

one more picture.

[img764]http://img.photobucket.com/albums/v217/ ... 0e68e2.jpg[/img]

this is about how far i can get before i get a few more parts in the mail.

[cbass]

Lookin good so are you going to use an ez81/6ca4 for the rectifier.

[wsaraceni]

is it safe to use 1/2 watt resistors for the 1k5 resistors on the el84s? it seems on the rocket schematic they ask 1 watt. liverpool layout is 1/2 watt. all i have is 1/2 watt metal film

[wsaraceni]

Lookin good so are you going to use an ez81/6ca4 for the rectifier.

yes. thats the plan. the PT is only officially rated for 1.5A on the 5v so i decided to just use the ez81 tap off of the separate 6.3v tap

[cbass]

You mean the resistors on the grids.I see no reason why .5watt resistors would be a problem.

[cbass]

nevermind

[wsaraceni]

yes. the grid. pin 2 on each el84. i guess the biggest issue will be making them sturdy coming off of the leads. double heat shrink should take care of it i assume

[wsaraceni]

a little more work done this morning. now i really can't do much more until the rest of the parts arrive.

test fitting leads

[img764]http://img.photobucket.com/albums/v217/ ... 29c283.jpg[/img]

[wsaraceni]

changed out the 50ohm resistor i mistakenly put in there for a 150ohm setup. didn't have the right resistor for that so i made a board that used the same holes to mount since all the leads are attached to the capacitor side except for the jumpers, i can easily swap out resistors without too much trouble with the soldering

[img764]http://img.photobucket.com/albums/v217/ ... 885114.jpg[/img]


also added the speaker jacks. stinks though, without a faceplate you need a few extra washers to get it nice and tight.

[img:764:1024]http://img.photobucket.com/albums/v217/ ... 4b9f54.jpg[/img]

and then i got to looking to make sure i'm wiring these things correctly. looks like the four posts on the back can just get tied to ground. the other two posts get tied to the imp selector. i numbered them 4 on this diagram. I'm pretty sure this is correct. can anyone confirm?

[img:764:1024]http://img.photobucket.com/albums/v217/ ... 0c8eb0.jpg[/img]

[wsaraceni]

i think i am done. i double checked it. had 2 of the B+ wires swapped. i checked everything else and think i am good. i've decided to hold off for the rest of the night, print out a new schematic, and go over it twice tomorrow night. if everything looks correct, i'll finish putting together my light bulb limiter and start it up!!!

[img:764:1024]http://img.photobucket.com/albums/v217/ ... 78f794.jpg[/img]

[wsaraceni]

it's alive. after dinner tonight i'll take voltage readings and maybe we can fine tune it a little bit with some help from the experts here. overall, i'm pretty happy with it. i played it attenuated through a junk speaker cab right now, but hopefully this weekend i'll put it through my 2x12 with blues unattenuated with a guitar that isn't out of tune and i'll get a better idea of how it sounds. it's not as Big sounding as the z-wreck i've played, and even less big than the rocket clones, but i think with a slight tweak or two it'll be perfect.

is it weird that I'm nervous playing it though. like it's going to blow up any second? not as nervous as i was when i found out the only el84s i had in the house were original NOS mullards i've had since i sold all my el84 amps a while ago. time to get some junkers this week for future testing


so here are the voltages i got. and just so everyone is aware. this is closer to a z-wreck 18 than a rocket 18.

V1
pin:
1)136.2
3)1.199


V2
pin:
1)252.8
2)158.6
3)157.8
6)158.7
8 )1.086

V3
pin:
1)237.7
2)39.9
3)57.6
6)239.7
7)39
8 )56.97

EL84s
cathode (pin 3) 11.74
pate (pin 7) 322
screen (pin 9)329

mains 122.8
secondaries 286
B+:
1:334.6 off of standby switch
2:320.7 off of choke
3:297 off of 27k resistor
4:251.6 off of 22k resistor
5:313.1 off of 20k resistor