Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: taddy on April 03, 2018, 03:54:45 am

Title: Positioning of filter caps
Post by: taddy on April 03, 2018, 03:54:45 am: Hi everyone,

I'm building a deluxe reverb without the tremolo section and using a Princeton chassis.

Because I don't have the tremolo module there is a bit of space and I was wondering whether I could put the filter caps for the power and preamp in the chassis next to the power transformer. Is this a good idea or is there a reason why the caps are usually underneath the chassis? Would it pick up hum being next to the PT?

Cheers

Tom
Title: Re: Positioning of filter caps
Post by: TIMBO on April 03, 2018, 04:13:29 am: There is no problem with the filter caps being on top of the chassis providing they are a cap can type with there terminals inside the chassis or as some of the Fender amps have the axil type filter caps mounted on top of the chassis then a protective cover is put over them.
Otherwise filter caps that are mounted inside the chassis cap be placed near transformers with no ill effect.
(https://i.imgur.com/foJdrP5.jpg)
Title: Re: Positioning of filter caps
Post by: sluckey on April 03, 2018, 07:03:24 am: That's fine. But the PR chassis has a cutout for a cap can. Why not put a JJ 40-20-20-20 in that hole?
Title: Re: Positioning of filter caps
Post by: taddy on April 03, 2018, 07:41:23 am: Well I actually bought a JJ can but then read some stuff on grounding - specifically that it was better to have the first two or three filter caps (plate and screens) grounded with the PT and bias and preamps filter caps grounded on the bus bar. As far as I can tell a can doesn't permit this because it has a common ground. If you guys reckon it would be ok then maybe I could stick with the cap can.
Title: Re: Positioning of filter caps
Post by: sluckey on April 03, 2018, 07:49:58 am: Ideally, using separate caps is better for the reason you said. However, there are plenty of successful amps that use a can cap, including the PR. Even my Sunn Sceptre uses a can. If I already owned a JJ can and a PR chassis I would definitely use them together.
Title: Re: Positioning of filter caps
Post by: taddy on April 03, 2018, 08:56:00 am: Thanks for the suggestions. Not sure what to do now!

In terms of spacing if I were to go for the separate filter caps like the deluxe reverb, would they be ok next to the PT within the chassis?

Is there anything that really shouldn't be close together?

Apologies for the endless questions. This is my first build.
Title: Re: Positioning of filter caps
Post by: sluckey on April 03, 2018, 09:10:30 am: You can stack them up so they are touching if you want. But if you are gonna clump them all together you kinda loose the advantage of using separate caps. May as well use a can in that case. Ideally, the best place for the caps in near the circuitry they actually power. Look at this page for some good pics of how to really take advantage of using separate caps...

http://el34world.com/Hoffman/AB763Project.htm
Title: Re: Positioning of filter caps
Post by: taddy on April 03, 2018, 10:50:51 am: Nice!
Thanks Steve!
Title: Re: Positioning of filter caps
Post by: Diverted on April 06, 2018, 04:31:05 pm: Hi Taddy,

Here are two ways I dealt with filter caps in two recent amps. I can't stand dealing with caps on top of the chassis and since I cut my own fiberboard I can always find enough room to fit the electrolytics underneath. To me it's way easier and a lot more fun. Good luck. First build is a 6G3 (caps on fiberboard) and the second (with can cap) is a Princeton Reverb.