Need Help With A 1978 Peavey 400B Mark III Bass amp

[steve2112]

Recently got a steal on this amp and I am new to repairs. Pots were very dirty and the inputs were super cracky. Several small capacitors have leaked and simple to replace.

I reflowed the solder to the inputs and that fixed all but one inputs. I am assuming the input jack is just bad and will replace.

Here is the main question, I want to replaced the large filter caps but i cant find replacements. They are listed as 5000 MFD 500v. I have been looking around and cant find any replacements. Am I missing something? Is there anything else i need to check?

- Steve

[nosaj]

Recently got a steal on this amp and I am new to repairs. Pots were very dirty and the inputs were super cracky. Several small capacitors have leaked and simple to replace.

I reflowed the solder to the inputs and that fixed all but one inputs. I am assuming the input jack is just bad and will replace.

Here is the main question, I want to replaced the large filter caps but i cant find replacements. They are listed as 5000 MFD 500v. I have been looking around and cant find any replacements. Am I missing something? Is there anything else i need to check?

- Steve

I'm sure it's a mistype as far as the 500v rating. I normally use 4700 uf 63 volt replacements. Your best deal I think on price for those is usually Peavey. Call them up they are super easy to deal with.

nosaj

[nickb]

My data shows the caps are 5000uF 55V. Do as Jason says.

[steve2112]

My data shows the caps are 5000uF 55V. Do as Jason says.

i missed type its listed on the schematics c34/c35 ass 5000uf/50v. Sorry about that. Still i could not found a replacement online. I have contacted peavey before and they were helpful on other things.

Also what would be good brand caps for these large caps and the other ones on the board?

-steve

[nosaj]

i missed type its listed on the schematics c34/c35 ass 5000uf/50v. Sorry about that. Still i could not found a replacement online. I have contacted peavey before and they were helpful on other things.

Also what would be good brand caps for these large caps and the other ones on the board?

-steve

Some people complain about Illinois caps but I started this in 2011 and I've never had issue with Illinois caps and I've used them quite a bit.
https://www.mouser.com/ProductDetail...3sN9Yk8Q%3d%3d
nosaj

[Enzo]

55v is not a standard value, 63v is the modern closest voltage. 5000uf is also not a standard value, 4700uf is the modern standard value closest. If you order 5000/55v caps from Peavey, they will send you 4700uf/63v caps.

Any brand Mouser sells will be fine.

Note, the original cap is not laid out to standard either, the legs on a modern cap will not fit right into the old holes. You will have to CAREFULLY drill some new holes in the board to mount the new caps. Or otherwise compromise.

[steve2112]

Ahhh. Drilling into the PCB seems like a little past my skill right now. Maybe i will just change the smaller capacitors that are leaky and see how it sounds from there.

[steve2112]

thanks

[Enzo]

The caps nosaj linked would not require drilling, but you would have to figure out some sort of support. I prefer to drill a litle and use "snap-in" style caps, myself.

[Jazz P Bass]

Are the power supply caps bad?

I have seen the 35 volt caps for the 27 volt supplies that feed the 15 volt regulators go bad more often than the big boys.

[steve2112]

Enzo, i will look into doing that. The board has lots of room on it so drilling might not be too much of an issue. I might measure them and do that last if they check out good.

I went through the schematics and made a list of all electrolytics caps. Should i replace all of them or just the 5 or 6 that are leaking? Are there any i should just replace no matter what. Everything looks stock in this. No mismatched anything.

- steve

EDIT: Are there any books i should keep by the bench while working on amps. I am new to this and have been reading up online and watch videos but i always like books for reference.

[steve2112]

So should i recap everything in the amp or only the bad caps?

Also it is calling from a 1000uf 35v cap. Is this the correct replacement https://www.mouser.com/ProductDetail...8H8ORCpA%3d%3d


- steve

[Enzo]

Sure.

Why don't you just get it going, then worry about wholesale parts replacements later?

[steve2112]

The bass amp is for my wife so i have to make sure its 100% good. I have to order all the caps since I am new and dont have any stock. I am using sprague caps because i heard they were good. Maybe i will just replace the leaking caps and get a few extra just in case. If i need to order the rest i guess i can always do that.

Just trying to figure out whats best practice.

[Bloomfield]

The general consensus around here seems to be that Sprague caps (electrolytic at least) are really overpriced, especially the vintage style 'Atom' series. So, unless you are really into preserving a period look, there is better value elsewhere. I've had good luck with Nichicon and Panasonic which are readily available at good prices from Mouser, Digi-key etc.