Tube layout question

[Paul P]

Switching the PT and OT, then squeezing the big tubes to within an inch of each other and the PT :



To within half an inch of each but not the PT :



Everything within half an inch :



Paul P

[MWJB]

There doesn't seem to be a significant advantage between 1" & 1/2" spacing, perhaps 1" would be more practical.

Somehow you need to get that PI nearer the power tubes. You don't want long grid wires to the PI grids or the power tube grids.

Perhaps moving the preamp tubes closer together & losing the choke would help you align things up better? I know you seem keen to use the 3 tube vibrato, but a 1 tube vibrato (6G16) would make life so much easier.

[Paul P]

Here is what the current layout looks like from underneath. There seems to
be no way around having a few long grid wires. Isn't it at least best that it
be the ones to the power tubes ?



For what it's worth a Fender 6G7-A Bandmaster has a few pretty long wires as
well, though not to the power tubes.

I turned the choke back 90 degrees to give it more room between the
tubes. Is this ok ?

The big alternative is to go with a 30" long chassis :



Or a 25-26" long one if I double up the tremolo and reverb :



I have been unable to locate a chassis maker that could do this for me.

Paul P

[MWJB]

Do you see that if you lost the choke altogether, you could relocate the PI tube to where it wants to be? You could save space on the 2 preamp circuit boards by mounting tone caps directly on to the pots. Then you could close up the gaps in the preamp tubes & free up some space.

A new chassis - I don't see why your chassis would need to be any longer than a Fender Twin style chassis? www.torresamps.com in the UK do a generic chassis that is the same dimensions as a Twin chassis, it takes 11 tubes.

[Paul P]

Say we drop the choke for now and put the PI tube in its place. With a little
fiddling things now become :



The drawing needs some cleaning up but you can see the general idea.

This has another advantage on top of shortening wires (though the really
long red one from the normal preamp is a bit longer than it was). If I can
shave just a bit off the width of everything I can get my reverb down off
the temolo's back. Moving some components to the pots should do it. I
also split the PI/Output board in two so that the PI tube is in between.
This is what really shortens the grid wires to the power tubes.

Thanks again MWJB.

Paul P

[MWJB]

Do you need to have a tube rectifier? Going SS will save more space.

Do you need a whole board for the bias? A short terminal strip could do the job if you're looking at a BF Fender style circuit?

Are you sure you'll need filament hum balance? You should not need this and it's taking up real estate.

Even when I'm working on a relatively simple circuit, I'll draw it...have a ponder...redraw it...have another ponder...and a week after being sure it's as good as it can be, it'll end up significantly different. I'm not deliberately dragging this out, it's just the way I go through the process. It's like the old carpenter's rule, "measure twice, cut once". So whilst I applaud your ambition and your experimental nature, don't be in too much of a rush to realise the design. When you're sure it's spot on, step back, sleep on it and see what comes to mind before you start punching chassis & boards.

[Paul P]

I also like to chew on things several times before starting to make anything.
You wouldn't believe how many times I've redrawn my circuit board layouts.
When I put them in the chassis I realized that the interconnecting wires could
be better placed to shorten them, so I went back over everything again. I'm
still in that process. It's a good way to learn the circuits and catch errors.

I can see that I might give the impression that I'm in a hurry. I was a bit
taken aback when I realized that putting everything in the chassis wasn't
going to be as straightforward as I thought. I've been working quickly
at my end in part to make it easier for you to see the results of your
suggestions. I have zero experience with laying out tube circuits so your
interest, and that of others, is priceless for me. I have prior experience
in just about all other aspects of amp building but tubes are something new.

And I have most of my parts, which I needed to do the layout properly, so I
guess I am itching a bit to start building but I'd rather wait until I'm very
comfortable with the design.

I can say that I've now learned the advantages of Fender's inline design.
The problems I'm having stem from having to bend this design back on itself
to fit in a shorter and wider chassis.

As far as removing the choke and rectifier goes, my original desire was to
produce a 'classic' high quality tube circuit, using tube technology as much
as possible, to get good hands-on experience with all the aspects of tube
audio (there's a romantic component in all of this, I'm sure). I'm not sure
whether or not I'm going to build more than one amp. I'd like this one to be
able to hold everything properly, even if some parts are ultimately removed.

I see this amp as a test bed for all sorts of experimentation and also something
that will be able to grow with my guitar-playing needs. For example, currently
I just play at home and probably don't need more than 5 watts output.
Eventually I'd like to play with others and then maybe I'd be better
off with the 22 watts of a 6v6 push-pull amp. If that isn't enough I can go
to 6L6s. I don't want to build a new amp each time. They are expensive !

So I'd like to have it all, but in stages. My plan is to get my amp up and
running with just the normal preamp and a single-ended 6v6 output. A
Champ. Once that is working properly, I'll add the second channel one
piece at a time. This is why everything is on separate boards. I don't
see myself doing the push-pull for a while.

The challenge with my approach is that I have to do the complete design
up front. I'd like to avoid having to modify the chassis once things are
attached to it.

The overall design is based on the 6G7-A Bandmaster for the preamps
(these may end up being blackface) and tremolo, the AB763 Deluxe
Reverb for the reverb, PI and push-pull output stage, and the Champ for
the single-ended output stage. Oh, and a Marshall 1987 for the bias
circuit.

Well, that was quite a bit. Now back to the drawing board

Paul P

[Paul P]

I worked some more on my design and am quite happy with the way
things are going. Everything fits inside and the wires are reasonably
short except for the long one in the normal channel.

The top :



Inside :



Front panel :



Paul P

[petemoore]

Shielding can also cause problems of it's own, I 1/2 understand...choosing to try to shield only the sensative wires toward the input...being none too sure about shieling higher gain wires.
I just put an 18w in a squarish chassis, most of the percieved issues about oscillations and noise were adressed in the first 10 hand-drawn layout drafts.
It's a much simpler amp, but no matter how I laid it out it seemed, there was a long 'sensative' or 'noisy' wire or component placement I didn't like.
So I picked a layout which placed most everything pretty well except a few wires, I chose to have two long input wires shielded those.
@@R@te pondering incorporating some shielding in the layout design is merely suggested, comments welcome...I don't know that much about it.

[Satamax]

P.S. That shield in the Hiwatt is probably to keep the heat from the output tubes away from the capacitors. After all, it has shields on the preamp tubes.

Well, it's for that and suposedely, (an opinion emited by some knoledgeable folks) to couple or decouple some magnetic/electric fields between the transformers so they don't go elsewhere.
I'm not sure for hiwatts thought, but that's the explaination given about it's cousins. Notice in the pic how the shield goes from PT's edge to OT midle of the coil. That's suposed to be the easiest path for something IIRC.

http://www.soundcitysite.com/sc_webp...6.htm#B120_2.4

[Paul P]

Here are some articles on lead dress :

http://www.geofex.com/Article_Folder..._tube_amps.htm

http://home.earthlink.net/~ayan/leaddress.htm

And here are some examples :

http://www.thegearpage.net/board/sho...d.php?t=176129

http://www.shopamiami.com/product.as...&pfid=AMI01701

Paul P

[Paul P]

After further review... here's what should be the final layout of everything.
The wiring will hopefully be a bit cleaner in real life, in the drawing I'm more
interested in seeing where each wire goes.



The big question is : will it be quiet and stable ?

The rear panel :



Paul P

[Bandit]

Well, there's more to this picture . I'm already up to a 17" x 10" chassis,
which is the biggest I can find (from Hammond). Here's the rest of it (it
still hasn't been 'wired', is missing some parts, and may contain errors) :

[ATTACH]1253[/ATTACH]

The view is from underneath inside the chassis. The transformers and tubes
are on the other side, on top, as in a hi-fi amp.

Starting at the top left the boards are preamp (normal), preamp ('vibrato'),
tremolo circuit. The small output board is for a single-ended output, to be
replaced with the pi-output board if and when I go to push-pull. The circuit
at bottom left is reverb.

There shouldn't be too much criss-crossing of wires since each tube is
close to its circuit.

Paul P

What software did you use to make these pic's?

[Paul P]

Take a look at the tenth message in this thread :

http://music-electronics-forum.com/s...ead.php?t=4742

Paul P

[Paul P]

A big thanks to all

I've been looking forward to writing this post since it means that I've survived
my first journey into amp building.

I'd like to extend a big Thank You to all of you that helped me along the way and
all you others that have contributed so much to this Music Electronics Forum
so that people like myself can learn about tube amps and how to build and
modify them.

I'd like to say a most special thank you to MWJB who gave me considerable
help at the very beginning and without whom my amp would probably have
turned out to be a big mess. As it is the amp is stable, very quiet and sounds
great. I will of course be playing with that sound once I've gotten to know
it a bit.

Here is the amp :




There will be some sort of plate on the front which will cover up the holes.
The rest is just woodwork.

Cheers,

Paul P