5F2-A Chassis and Control Board Idea

[humbug]

Hi All,

First time builder here. I bought Doug's Princeton kit complete without the chassis. My idea is to place the chassis on the bottom of the cab with the tubes facing up, then have a plate on the top of the amp for the instrument input, pots, pilot light and switch. Obviously, these will have to be connected with wires down to the chassis. And I assume that this top plate would have to be grounded to the chassis as well.

I've seen a few pics of this kind of layout on Google etc. It seems to me that this would allow the heat of the tubes to dissipate better without going into the chassis as with the traditional Fender design with the upside down tubes.

Are there problems with this idea? Will it add lots of hum from the longer wires from the input and pots or can this be negated with shielded wire and careful placement? Thanks in advance for your help.

Steve

[eleventeen]

"Will it add lots of hum from the longer wires from the input and pots or can this be negated with shielded wire and careful placement?"


Unpredictable. But you're certainly asking for it.


You say top "plate". Hum reduction to usable status may demand you completely enclose your top chassis element. And not only that, but shield the AC elements (switch, pilot lamp) from the audio wires. In other words, top thingy may have to have internal pieces of sheet metal separating the AC from the pot. Shielded wire, yes, definitely.


But, I would encourage you to try it, without carving up wood for a cabinet. Or, making your cabinet with a top cutout such that if all else fails, you can always revert to the standard 5F2 upside down all-in-one chassis by moving the main chassis up to the top.

[John]

 A couple other forum members have done that, threads are on here documenting everything. Do a forum search for upstairs/downstairs, or something like that... I just forget what it's under.


Anyway, it is doable. Good shielding around the wire bundle will of course be a must. I prefer tubes up myself.

[Willabe]

Welcome!   

It seems to me that this would allow the heat of the tubes to dissipate better without going into the chassis as with the traditional Fender design with the upside down tubes.

Are there problems with this idea? Will it add lots of hum from the longer wires from the input and pots

There's not really that much heat from a Princeton amp.

I think it will be more trouble then it's worth.

Traynor made combo amps with the tubes mounted upright but they put them in a larger cabinet with a shelf that the chassis sat on and was bolted to separating the chassis section from the speaker section of the combo cab. That way all components were inside the chassis and were shielded by the chassis with no long wires connecting between 2 chassis.

[humbug]

Thanks so much for your replies. This gives me some good things to think about. Maybe I'm over-thinking the whole thing. I'll let you know what I've decided. I'm taking my time with this project since it's just a fun summer learning/building pastime.

All the best,

Steve

[humbug]

I found a picture of what I was thinking about which is attached. This is *not* my amp or picture which was found at

http://www.chambonino.com/construct/const16.html

I notice that the fuse/power switch wires are separated from the pots wires. Just still thinking.

[Ed_Chambley]

If it is simply heat you are concerned with it would be much easier to mount a fan and build it the standard way.  I prefer tubes up as well, but in my original old fender amps and even tube up marshall amps I have slow running fans I swipe from dead computers.  The amps run so cool you can touch the tubes.  You just don't want the fan pointed directly at the tubes.

As Brad said, you really do not have much heat.

[John]

11teen, Brad and Ed are all correct.  That said, the reason we (or I) do stuff is just to see if I can and if it works. 

[Ed_Chambley]

11teen, Brad and Ed are all correct.  That said, the reason we (or I) do stuff is just to see if I can and if it works. 

Absolutely!  I have a couple of experiments that went very well and then I also very good at removing solder.

[humbug]

Thanks again for taking the time to respond to this thread. I did finally decide on the design and I will have the chassis on the bottom of the amp with the controls on the front face and the tubes sitting upright. I'll post pics when I'm all done. I'm just about finished with the amp proper; the box is next.

BTW, I found some old cedar planks in my wood storage that I plan to use uncovered. It's really beautiful old wood that is true 3/4" thick (30+ years old wood I would guess). Again, I'll post pics.

I should add that I had several questions as I was putting this amp kit together, but I just searched this forum and found all the answers. What a great resource for the first-timer!

Steve

[eleventeen]

I encourage you to proceed with your project as envisioned. It's how you learn.


The *only* thing I would suggest is, to select a lower chassis large enough so that if you simply cannot get the hum down to where you want it, you can move the tone controls and produce a more conventional single chassis. Unless of course you're already committed.


After all, if the amp is at the bottom of the box, it wouldn't seem to matter if it's a couple of inches longer....makes construction easier.

[humbug]

Thanks eleventeen,

I think my description was flawed. I settled on having everything on one chassis but I'll be putting the chassis on the bottom of the cab or box with the controls at the bottom on front (I know some people use a shelf above the speaker with the controls on top). It's a quirky design in some ways, but I think it will work for me. :)

Here are two pics but it's still unfinished. I just put one tube in to show where they go. :)

Best,

Steve

[TIMBO]

Hey mate, just for any future builds, the up/downstairs works well.
This is a HIGH GAIN build with lots of tube and they wouldn't all fit in one chassis.
http://el34world.com/Forum/index.php?topic=15795.msg153990#msg153990

[humbug]

Good to know. Thanks.