6V6 Rocket

[Structo]

Hi guys,

I was hesitant to even post this here because by comparison to most of you guys builds it does not begin to compare.

After seeing Rawnsters Big Bottle Rocket and RJ's I had to give it a try.
But this was a "build an amp from what you have on hand" type build.
I did have to buy the choke from AES and a handful of caps and resistors.
But I had the circuit board, eyelets, etc.
It has the Rocket front end and PI.

This was a late 50's Hammond organ amp that I gutted and originally I built a 5E3 type amp in it. It has a nice set of Sylvania 6V6GT's and RCA 5U4 rect.
Later it became more of a Plexi type circuit.
This time around it has a Rocket preamp and PI.
This chassis used to be 21" long, but using tin snips and a hand brake I shortened it to 14". In hindsight I should have made it longer........
I had to add a 12AX7 so the tubes are very close.

Anyway, the power supply is quite a bit different using a 5U4 and a JJ cap can, the B5+ filter cap is on the board because there wasn't any room elsewhere.
It is very tight in there and it was like working in a sardine can.

It took me a while to get the preamp voltages down to Rocket spec, at first it didn't sound good at all. Sputtering, motorboating, etc.
But once I got the voltages close it became a different amp.
I am loving it, quite a departure from my D'lite or the Marshall I have.

Even with the close proximity of the parts, tubes and inductors, this amp is pretty darn quiet and only hums when I have a single coil guitar plugged in and the volume is turned up high.
This is a steel chassis so I tried to tie all of the preamp grounds to the same point near the input.

Of course the power supply section in this amp is different from the Fischer Rocket. No stack of caps and the dropping string is different because of the PT.
The OT is the stock D'Lite OT with the 8K primaries wired to the 6V6's.

Eventually I think I will build a proper Rocket with reverb inside and nice new aluminum chassis.

[IMG:800:440]http://i23.photobucket.com/albums/b392/ ... G_0536.jpg[/img]
[IMG:793:388]http://i23.photobucket.com/albums/b392/ ... G_0538.jpg[/img]

[IMG:799:568]http://i23.photobucket.com/albums/b392/ ... Layout.jpg[/img]

[rooster]

Cool, Tom. I never got the bug to buy those old Hammond chassis but a lot of people I run into do/did. And here you actually did something pretty advanced with it, relative to creating a preamp and adding a couple of knobs, etc.. Kudos!

So I'm impressed. Sometimes, too, it turns out that the 'amp in the crazy package' can be the sweetest one you ever built - been there.

[Cliff Schecht]

Well, how does it sound?

I was thinking about doing a quad 6V6 version of the rocket myself. I still have that OT that is 4400 Ohms CT and has a max current of 70mA. Four 6V6's are right on the edge of what this OT can do though and I think that four EL84's would just be past the limit (plus I don't have a lot of EL84's on hand). I may do this build eventually if the right parts come my way but as of now, I really want to do an 807 Bassman build .

[FYL]

I really want to do an 807 Bassman build .

Tsk, tsk, tsk.

[Structo]

I'm pretty happy with the tone from it, but never having heard or played one in person I don't really have a benchmark.

I may play with a few values such as the second stage cathode resistor and the PI cathode and tail values.

Heck, I might even commit sacrilege and try a master volume on it.

Yesterday I was playing through it and had a tubescreamer and Boss reverb into the front end.
The screamer seemed to create some fizz I hadn't heard before so there could be some ultra sonic oscillation going on, but without a scope I am only guessing.
Power tubes are not redplating (yet). I have the 6V6 biased at around 11 watts.
I really need to get a scope and sig generator.
But, I am still unemployed so those toys will have to wait.

[strat_addict]

Any chances for sound clips?

[andrew]

That looks like the Lowery organ amp chassis I have my 6v6 Rocket in. Tight fit. I have a can cap mounted on top. I have it in a 1-12" combo.

[M Fowler]

Tom, I like your new amp nothing wrong with that.

Thanks for the layout you modified as well.

Oh, you asked me awhile back to let you know when the honey moon with my new Rocket Reverb was over, well I still love that amp.

Mark

[Cliff Schecht]

I really want to do an 807 Bassman build .

Tsk, tsk, tsk.

I thought it would be cool being that I have a fairly large stock of NOS 807's and 1625's (dual heater-voltage version) which in my experience make fantastic audio tubes. My first tube build used an 807 in the power amp and while the clean sound was pretty lackluster with the 6AU6's, the distortion sound with a good pedal in front of it (modified Boss BD2) had a fantastic bloom that I'd never heard clearly before this amp.

[FYL]

I thought it would be cool being that I have a fairly large stock of NOS 807's and 1625's (dual heater-voltage version) which in my experience make fantastic audio tubes.

They do. And quite cheaply to boot.

Just think RF when it comes to topology / lead dress and keep the screen supply very tight.

[Cliff Schecht]

I haven't had an RF problem with 807's yet. Like you say, they are very cheap and at the same time, they're high quality tubes. Small ferrite beads or resistances placed in series with the plate caps and small grid stoppers are usually enough to keep these suckers from oscillating. I've actually never had to use any plate resistors, but that's an old trick to help subdue oscillations. Then again, good lead dress is usually all you need for a stable lower gain amplifier.

That amp is currently just a thought really but I have some great 5-pin ceramic sockets that I bought pretty much with this intention. My dad has been collecting 807's and similar RF tubes at hamfests for many years (but not enough audio tubes ) so he has a great stash that I'm slowly weaseling away for audio projects.

[paulster]

Wow, compact!

Nothing like setting yourself a challenge, but it looks good.

[Structo]

I'm going to make a head shell for it.
This is the first time that I felt the amp sounded good enough to do that!

Now I got to figure out how I'm going to do that with a Skil Saw and jigsaw.

[Structo]

Something else I was wondering about, it seems that with this amp, even though I have 1K screen resistors and the choke between the plate and screen nodes, that the screen voltage is hardly lower than the plates on the 6V6's.
Is that common with 6V6 or is it just the way the Rocket power supply works?

Thanks, Tom

[andrew]

Structo. I'm liking my Rocket this time with a pair Sylvania 6v6s I bought from Mr. Kilgore. "greasy" is how he described them. I tried it once before with JJs but these sound much better. I've had that same experience with the screens being one volt below, above, or the same as the plates when using KT66s.