Rocket hybrid layout

[fabiomayo]

Hi, guys!

I just started researching the Rocket information
you all generously shared! I was planning on a Voxy
build and figured the Rocket would be my best bet.
I added Dana's VVR, different power supply layout
(distributed) and an EF86 Vox AC15 channel.
Dedicated bias resistors for each EL84 pair (for
pulling two tubes out for half-power), and I thought
of adding a tremolo, but the layout issues made me
delete it. Elevated heaters also.


This is the layout I've drawn. Can anyone please take
a look at it for potencial problems? Do you guys think
it's a waste of time and I should just a build a
straight up Rocket clone instead?

Thanks!

[Zippy]

You don't have enough knobs!

Why not add a mid control?

[fabiomayo]

Well, the tremolo would add two more knobs

Anyway, no thoughts on whether this is a good or bad idea?

The biggest difference from the Rocket is much less filtering... I guess
I could increase that easily....

[Ron Worley]

Your OT is rather close to your input valves, my reading indicates that it should be over by the PT, but I've proven many times that I am no expert....

Ron

[Fischerman]

fabio,
Are you familiar with the Matchless DC30? It's basically exactly what you're doing...a Vox Top Boost channel plus a Vox EF86 channel into an AC30 power amp. The only 'twist' is that they have dual rectifier tubes wired in parallel...you can use two 'lesser' rectifiers (like two 5V4's or even two 5AR4s for minimum sag/drop) to get different voltage drops/amounts of sag. Check out Ceriatone's schematic/layout.

I wouldn't go with less filtering...these things can ghost a bit and reducing the filtering is just asking for it IMO.

[fabiomayo]

Ok. Thanks for the tips. What about the layout? As Mr Ron pointed out
the OT may be too close to the pream tubes. Is it TOO close or enough?
Any other issues?

Thanks!

[Fischerman]

I dunno fabio. Here's a pic of my most recent build...a 100W SLO. It has the OT mounted on the opposite side of the chassis as the PT. I like the way the trannies and tubes are laid out...I think I'd like to do more amps like this. The amp is quiet and stable and sounds great so there doesn't appear to be any 'proximity' issues. That preamp tube closest to the OT is the input tube.
[img:800:600]http://i108.photobucket.com/albums/n4/m ... pFront.jpg[/img]
[img:800:600]http://i108.photobucket.com/albums/n4/m ... tGutRP.jpg[/img]

[skyboltone]

I don't have a problem with it. In old Fisher Stereo equipment you will sometimes see a chassis mounted "shield" between the OT and the output tubes. This shield is simply a piece of aluminum angle a centimeter or so on the mounting side and as tall as the output tubes.

Such a shield could be used if the OT talks into the pre-amp section on your amp. I wouldn't worry about it.

I would however rotate the choke 90 degrees with respect to the power transformer.

I've considered board mounting the grid, screen, and cathode components adjacent to the tubes as you've done. I like that. It frees up a mile of chassis for filter caps too.

Good job.

[Stanz]

There is a weak spot in the magnetic field of the transformers along the plane of the laminates (stronger fields on the bell ends). Just make sure the orientation is such that the laminate's plane is aimed at the tubes. Looks like you already have that taken care of. There would seem to be an added bonus of moving the OT away from the field of the PT (which is why the PT usually has its weak spot pointed at the OT).

[fabiomayo]

Thanks, everyone!

I'll give that layout a go. I still need a few parts so it'll be while before
I can actually build it. I'll report back when it's done. In the meantime,
any more thoughts? Lead dress appear to be ok?

[skyboltone]

There is a weak spot in the magnetic field of the transformers along the plane of the laminates (stronger fields on the bell ends). Just make sure the orientation is such that the laminate's plane is aimed at the tubes. Looks like you already have that taken care of. There would seem to be an added bonus of moving the OT away from the field of the PT (which is why the PT usually has its weak spot pointed at the OT).

Hmmm. I thought it was because we didn't want the transformers interfering with each other. I'll take your word for it though. I never investigated it, I've always just made sure that adjacent transformers/chokes had their laminations 90 degrees apart.