66 Rocker - AKA 66 Rocket ...Eventually the 66 Rockster

[RJ Guitars]

Hey guys,

I've been started at this for a while and there seems to be several of you on the parallel path. I'm not sure whether the right idea is to use 6V6's, 6L6's, or KT 66's, but the cool thing is that "all of the above" will work.

I'm ready to mount transformers and start wiring...

This is an an econo chassis that I had the guys at the shop fold up for me. I had this one powder coated but I'm not sure that is the best thing to do if you still need to make a few holes. It's a tough finish but it will still scuff if you wrestle it around on the bench or hit it with a tool. I've got a bunch of these in bare aluminum that I'll pass along reasonably if anyone has the urge to build along.

rj

[Structo]

Are they drilled and punched?

[RJ Guitars]

Are they drilled and punched?

I can do them either way. If it looks like a group project I'll pass them along pretty reasonably. I'd really enjoy the company if there is interest in this build.

No holes but with IEC punchout - $45 (includes the bottom cover)
All the holes and IEC punchout - $55 (same)

They chassis is .090 thick 5052 alloy Aluminum and the bottom cover is .032 thick. They are standard Wreck dimensions and I have a couple with no IEC socket if that works better for somebody.

thanks - I's like to see your ideas that go along with the interest in this.

rj

[Zippy]

Is that drilled for SIX knobs?

Caution: This is not your mother's Rocket.

[RJ Guitars]

Is that drilled for SIX knobs?

Caution: This is not your mother's Rocket.

Six - no just five. I didn't mind adding a mid control (5th knob), but a sixth knob is just going a bit too far... You must be seeing the hole for the input jack. Also, no bright switch. So far nobody had been asking for that option on a Rocket. We'll need to hear it to determine if the their are any tonal deficiencies in the Octal configurations, then review the tonestack values.

rj

[drew]

It looks like six to me, if one of them isn't supposed to be for a bright switch.

[RJ Guitars]

It looks like six to me, if one of them isn't supposed to be for a bright switch.

Dang, you are correct.... what was I thinking? oh yeah, it was just a math test for you guys, i knew it was six...


... out of the fog, it's kinda coming back to me. This was originally something I pre-drilled for an Express build. I recall being a bit miffed at myself because I got so enthusiastic in drilling holes that I went oversize on the bright switch... thus the reason it appeard to Zippy as a SIX knobber.

rj

[Normster]

Just finished a 2x-EL34 Rocket. Very pleased with the outcome. It's not quite as chimey as the 4x-EL84 version, but it's got a little better mid-range girth and still maintains a lot of that percussive quality when palm-muting lower notes. It's not better or worse, just a little different. I've never played an AC50, but the circuit is similar so maybe that gives you some indication of what the result will be (versus AC30).

[Zippy]

Dang, you are correct.... what was I thinking? oh yeah, it was just a math test for you guys, i knew it was six...


... out of the fog, it's kinda coming back to me. This was originally something I pre-drilled for an Express build. I recall being a bit miffed at myself because I got so enthusiastic in drilling holes that I went oversize on the bright switch... thus the reason it appeared to Zippy as a SIX knobber.

Input - Volume - Treble - Mid - Bass - Master - Cut

Works for me!

You can always put the slope shift resistors, bright caps, and mid boost on pull switches later.

Whoops, gotta duck and run. It's those #$)(*@ 'Wreck Police again.

[Zippy]

Just finished a 2x-EL34 Rocket. Very pleased with the outcome. It's not quite as chimey as the 4x-EL84 version...

Am I correct in recalling (from another thread) that you are running this in fixed bias? Might the difference be there? I have seen some amps that claim a "Chime Switch" that adds/disconnects the bypass cap on the output cathode resistors. Any other differences in your output section?

This could be a call for the fixed bias/cathode bias challenge - even if I recall some members saying that it doesn't make a difference in their amps (not tested in Rockets as I recall).

[Normster]

It could be the bias. One of these days I'm going to build a fixed/cathode switchable bias amp just to hear the difference. The other variable is the transformer set. The EL34 amp uses a set of Pacific transformers while both of my EL84 Rockets used Heyboer. Could also be tube choices, etc. I tried a set of GE 6V6's and hated them. Didn't try any 6L6's and don't have any KT66's.

Since RJ has the chassis very reasonably priced, I think it's definately worth the trouble to build one and find out if you like it.

[RJ Guitars]

It could be the bias. One of these days I'm going to build a fixed/cathode switchable bias amp just to hear the difference. ...

How close are we getting to a 59' Bassman or an early Marshall if we are talking about a Rocket front end and a set of fixed bias 6L6's or El34's on the output section? Real close it would seem. (Zippy pointed this out, I can't take credit for it).

I am going to build with a cathode biased circuit to start with. I have high hopes for the 6V6's, although I am also a bit concerned that nobody has built an Express with them and wants to brag about it. I know that might be apples and oranges, but I want to keep an open mind so that I am quick to pop in something else, including a set of EL34's if I need more mojo.

I am drawn to the 6V6's in part because of all the rumors of how smooth they are with this preamp.... may it be true!

rj

[RJ Guitars]

Well, Give me a few weeks confined to a small town paralyzed by snowfall, and eventually I'll get something finished...

The progress on this has been on and off for weeks so as I saw the finish line coming today I was a little apprehensive, thinking that with so many interruptions I probably forgot something. Plus, this was a new circuit to some extent... 6V6's in for the normal quad of EL-84s.

Rocket Schematic - swap in two octals for four 9 pins
Custom wound power tranny - 245-0-245
Stancor 46326 Output Transformer
Olson Audio 209 choke
My own Chassis and circuit boards

I haven't been able to find any information on the output transformer or the choke. The hole pattern on the output was identical to the Heyboer/Toneslut so I just decided I'd try it and see how it sounds and swap in a new OPT if needed.

Well wonders never cease, it fired up and worked first crack out of the barrel.... that doesn't always happen, especially when I've changed as many things as I did from the previous Rocket builds. I'm not convinced I've got the tone-stack right. I added a mid control but I didn't have a 25K pot so I need to revisit that when I get the right pot here.

After I did the initial test to see if there would be smoke and flames, I put good tubes in it. It has a really pleasant early breakup but never gets mushy at all. Kind of has a crisp crunch to it, even at low volume levels. I put in a set of EL-34's and it was thicker and smoother with added harmonic character but the overall volume isn't all that loud. Still lots of work to be done and other speakers to try.

Overall it seems pretty cool but not the same as my other Rocket builds (why would it?). Lots of tests yet to come and I have an exact duplicate of all the parts (cheap) if someone wants to build one. I would love to have some company in tweaking this thing.

rj

[RJ Guitars]

I tweaked on my build tonight and put in a 50K pot for the mid control, plus wired it so that it didn't work backwards - all is well!

It also occurred to me today that I forgot the bypass cap on the output cathodes. Added that and it chimed things up, added some bass, and increased the clean headroom a bit. At this point it is more like the EL-84 Rocket, but yet still a unique beast.

Zippy brought me a pair of Valve Art KT-66's to try. Since this is a cathode biased amp, there is not much effort to make them work. Even if the amp didn't sound good, just the look of things make it a super cool amp.

The only thing I can say is that the Tone Police will be all over this. In a few words - way too cool and highly addictive. Maybe like great sounding EL-84's on steroids. Full, chimey, crisp, what's not to like?

I also tried a set of reissue Mullard EL-34's. They sound extremely good also, but not quite as chimey as the KT-66's. I'm getting ready to go try a set of old stock 6L6's and anything else I can find that will fit in there.

More reports to come...

rj

[bluegate]

Looks very good, I also see Amperex Bugle Boy & GE 12AX7