Incredibly Ignorant Questions About 5f6a Clone Filter Caps

[The New Steve H]

I'm building a 5f6a Bassman clone (head only), but I'm not using a kit.

I'm running into some confusion about the filter caps. I can't find out how they're usually mounted. I've found various photos of what appear to be filter cap arrays covered with little metal boxes.

Questions:

What's the best location for these caps?

Do I want to put a box over them to reduce noise?

If I use a box, should I use steel to resist magnetic fields, or will aluminum do? I can machine a box out of aluminum pretty easily, but making a steel box will be more of a pain.

If I use a box, does it have to cover the capacitors on all sides, or is it enough to have metal between the caps and the rest of the circuitry?

Right now, I'm planning to use a U-shaped aluminum channel for the chassis. The U will be positioned so it opens downward. The power transformer will be at one end, sunk into a rectangular hole in the top of the inverted U. The output transformer will be next to it, situated so none of the laminations are in the same plane. They'll be above the aluminum.

The preamp and inputs will be at the far end The rectifier will be the closest tube to the transformers, followed by the power tubes. All tubes will stand upright on the top of the U, so they will look cute. The preamp tubes will be in shields.

[Gibsonman63]

Welcome New Steve.

Fender mounted the filter caps on the underside of the chassis, the side with the transformers and tubes. The metal box is mainly for safety because you have the full B+ voltage exposed otherwise. You can order the boxes from Hoffman amps and others fairly cheap. The Fender made them out of steel.

Hoffman has some nice views of Fenders to get a better idea.

Hope it helps.

[M Fowler]

The OT on a regular 5f6a isn't right next to the PT if I remember correctly.
On my combo type with stock channel chassis I had plenty of room to add caps using two terminal strips between the PT and OT inside the chassis.

I guess your making a head version but still using the same type of chassis as the original correct?

You could mount caps on a turret strip or eyelet strip on the outside and cover with metal can. Or you could use can caps.

[The New Steve H]

Okay, so it sounds like I'm fine as long as I don't go through with my plan to lick the capacitors every time I play.

I'm not using a standard chassis. I'm using heavy aluminum channel. I tried to upload a cell photo, but my stupid AT&T phone service decided to take 9 days to get the shot to my email.

Edit: took a photo with a real camera and attached it. The parts are not attached, and I haven't drilled yet.

[The New Steve H]

Wait...hold it..."can caps"? Aren't all electrolytics can caps?

[NickC]

Wait...hold it..."can caps"? Aren't all electrolytics can caps?

Some electrolytics are axial type.

In this photo:

http://homepage.mac.com/swamptone/NickTek-Top2.jpg

The two big blue caps are cans in chassis mounts (the leads are on the inside .... through the chassis) ..... the board mounted ones are axial lead type electrolytics.

[The New Steve H]

Okay. I thought "can" just described the can-like packaging. I didn't realize a cap with axial leads was not considered a can cap.

[Colossal]

Okay, so it sounds like I'm fine as long as I don't go through with my plan to lick the capacitors every time I play.

Hahah, The Old Steve did that just once. He's not around anymore!

[M Fowler]

So that's what happened to Old Steve huh!

I like can caps take up less space and work out great.

Mark

[The New Steve H]

I ordered them accidentally last time. Just seemed like the right choice.

[surfsup]

I tried to upload a cell photo, but my stupid AT&T phone service decided to take 9 days to get the shot to my email.

At&t blows! My wife has them. She will text me that shes on the way home and my phone will get it when were going to bed. Seems to always be att.

[Super_Reverb]

A few suggestions to consider:

1) Place the preamp and power amp tubes in row(s). I think it makes sense to have the power tubes a little closer to back of chassis (for cooling) and preamp tubes a little closer to turret board for shorter wire runs. Checkout how most guys layout the express chassis.
2) Layout your OT and PT to minimize wire run length, i.e., PTs work better on one edge of chassis close to fuse, IEC jack, and power switch.
3) OT should be transverse with respect to PT/choke to minimize 60 Hz magnetic induction into OT.
4) Complete planning for your turret board before you start metal work on chassis.
5) Avoid signal overlap - signal should flow from one side of board to the other.
6) Keep OT wires away from preamp to minimize parasitic feedback (oscillation)
7) Read this info: http://www.ampbooks.com/home/classic-ci ... n-summary/

Don't mean to be insulting to your skills, in case you already know all this, but wanted to pass on a few hard learned lessons and some tribal knowledge.

Take your time. You only build it once, but you'll enjoy it for years.


cheers,

rob

[diagrammatiks]

ooh I like your layout.

You should think about putting the choke in between the pt and the ot though. It will help shield one from the other.

Whether or not you use a fender style cap can is really up to you.

The 5f6a is specced for a 320/325 type power transformer which will put out 455 volts unloaded. That means you need to either use 500vdc electrolytic caps or put 2 lower voltage caps such as 350/385 in series.

New production capacitors are much smaller then the old ones for the same capacitance so you should be able to fit them under the chassis if using 1 cap per filter.

[Cliff Schecht]

I use "underrated" caps in my personal amps on occasion. If you do so you just have to be careful about running the amp without tubes. If I'm doing this then I'll use a variac to throttle down the voltages for initial testing. Since I always set my bias way to cold first and bring it up from there, this doesn't cause me issues. Gotta be careful about overvoltaging caps for too long, it'll kill the caps very quickly if you apply voltage for more than a few seconds. Heck even this is enough time to kill caps if you are going 50V+ over the rating. Caps usually have a pulsed voltage rating that is somewhat higher than the DC rating, but once again you will kill them very quickly if you aren't careful. It's always good to be safe and use caps rated for the unloaded voltage of your amps, but sometimes I just don't have that cap on hand..

BTW this is terrible advice .

[rp]

Lots of ways to do these things. Here's what I learned over the years:

Wiring layout is critical, even in an old school modest gain amp. Newbies don't realize this, they think it's like wiring up a toaster. They think it's purely mechanical and try and make it pretty as #1 goal, but I've built amps I had to tear apart and rebuild completely because of oscillations. Sometimes an amp won't oscillate in the audible range but will sound like pooh even though you connected everything perfectly and chances are it's your wiring. So, if you are going to use a board then you should stick to tried and true layout, otherwise you must pay close attention and learn and understand your low and high power wires.

I'm not saying you shouldn't be creative, just giving you a heads up. One way to improve your odds here with an unorthodox layout is to go point to point, or partial ptp on critical areas, but that also has its luck and a learning curve, but more about avoiding a cluster f*ck that you can't get a soldering iron into. I do ptp mostly but I might spend a few nights for a week drawing it all out over and over and finally to 1:1 scale, till I get something I feel good about.

As for your cap placement, with what you are building I would say to to it Marshall JTM45 - JMP50 style - they are just tweed Bassmans with an English accent.

Google Images is your friend - just goggle jtm45 etc

FWIW: here's my way of doing a 5F6A. Like I said many ways, just watch the grids.