Filter Caps On My Marshall 4010

[Gary_S]

I'd like to know what part of the amp is powered by the 3 big filter caps. In my books it tells me that certain caps control the output tubes etc. others the preamp tubes.

I take it the one directly under the PCB powers the preamp tubes because it's near them, but how many? does it power all three? or just one or two?

[alerich]

From the schematic it looks like there is a pair of 50uf caps immediately after the rectifier diodes. This is the first filter stage. This feeds the output plates then the choke and then the output screens. A second pair of 50uf caps is just after the choke and provides filtering for the PI (V3) and V2. A third pair of 50uf caps after that provides filtering for the V1 stages. Can't help with physical location without the amp in front of me. The power rail is usually pretty easy to trace out in an amp as long as the caps are not hidden by a PCB. This is especially so in a Marshall amp that uses cap cans. Just start at the PT and follow the wires. Generally speaking, the proximity of the caps to a certain portion of the circuit usually means those caps are the filters for that circuit.

[HotBluePlates]

Ultimately, all of the amp is powered by the first filter cap stage, but there will be a choke or resistor between it and successive stages.

So not every portion of the amp gets the benefit of filtering from all of the caps. However, in most amps, the earliest input stages do get the benefit of filtering from all the filter caps and have the cleanest d.c.

[Gary_S]

alerich: that helps me a lot understanding what corresponds to what. Much appreciated.

The first two caps  are at the far right looking into the chassis with the controls towards you over where the PT leads are. The third is under the PCB almost in the middle of the chassis. This is the awkward one when putting in new filter caps. 

Cheers again guys for the help.

[alerich]

That circuit is the greatest rock amp of all time, in my opinion. I had a 1978 2204 head that I sold to Randall Aiken back in the mid 90s. I regret that to this day.

[Gary_S]

That circuit is the greatest rock amp of all time, in my opinion. I had a 1978 2204 head that I sold to Randall Aiken back in the mid 90s. I regret that to this day.

Oh yeah it really kicks out some massive power volume and tone. I thought about buying one of these turret boards that guys are selling on the market these days. There's one all wired up for the 4010 circuit that would suit the combo and head. I was thinking about maybe getting it and taking the PCB out eventually.

IDK though, seems a kinda shame when i have it working well now. You just read and hear so many people running PCB's down and saying turret boards are far superior, that got me thinking "if this sounds like this now, what would it sound like rewired with a T board?"

Here's a link to the board below:

http://www.ebay.co.uk/itm/Turret-Board-Marshall-50W-100W-JCM800-2204-2203-DIY-Kit-guitar-amplifier-/121018701868?pt=UK_Sound_Vision_Other&hash=item1c2d46d82c

[John]

Gary, only my opinion but if it's working well now, no reason to replace the PCB until you have to. From what I've read, there's nothing at all wrong with a properly constructed PCB made with good materials, especially if the designer gave thought to how the heater traces go and that sort of thing. Of course the problem is, they're often used in "price point" amps so everything is done fastest and cheapest, with cheapest board material and components, so people just assume that all PCBs are trash.

Naturally, a nice turret board is much easier to tinker with. Not that we ever tinker. 

[alerich]

IDK though, seems a kinda shame when i have it working well now. You just read and hear so many people running PCB's down and saying turret boards are far superior, that got me thinking "if this sounds like this now, what would it sound like rewired with a T board?"

I think much of the PCB versus turret board construction stuff is hype from a sound quality point if the component quality is equal. I don't think you'd hear a significant difference. Soldano even uses PCB construction. Turret board designs are easier to maintain and modify. For that reason for any new build I'd avoid PCB construction but I wouldn't gut a properly working amp unless I was planning some serious mods. That circuit needs no mods. It is perfection as it is. I have seen guys gut reissue Fender amps and outfit them with turret boards and claim a night and day difference. Of course, these guys were selling that service. I'd like to do a double blind A/B test with one of those sometime.

[Gary_S]

Thanks guys. Yeah i think i'll leave well alone until it's a necessity. i like tinkering but i've already spent ages tinkering with this amp and working on it replacing stuff. It had lain for a while and i hadn't been plugging in for a long time so i thought i better do some replacing of parts, bearing in mind the amp is a 1982 model, i bought it brand new so i've been the only owner.

Anyway i replaced the filter caps, coupling caps, put in some new tubes rebiased and so on. Plus fixed that problem i had with the negative voltage bias supply to the power tubes. So i really don't feel like doing anything else to it just now and just want to plug in and play now

As far as the turret board v's PCB: IDK, i'm not experienced enough to judge really. But reading a lot of guys they tend to down PCB based amps because the board is co-planar, all the components in one plane, rather than being wired the old way where things were not like that. They say there's a lot of stray capacitance problems with PCB's. I don't know about that, as i say i'm not experienced enough to judge but you guys will know better than me, what do you think?

I tend to think that on a well set out PCB you'd be hard pressed to hear the difference, i may be wrong though.

I suppose it's like everything in life; everyone has their own opinion about it and preference.