Electrolytic Cap values for a '68 EVH era Plexi.

[cole]

Hi All,

I have some idea from scouring various posts about the caps used for filtering (electrolytic caps) on this version of the '68 Plexi.

I have come up with this:


(2) 330uf @25v or (1) 320uf @25v and (1) 330uf @25v (as per Ralle Spec)
(1) Dual 32uf @450v as per PDF or (1) Dual 20uf (as per Ralle Spec)
(2) 10uf @150v
(2) 100uf @500v and (2) 32uf @500v or (4) 100uf @500v (as per Ralle Spec)
(1) Dual 50uf @500v single can (for outside top of chassis)


If anyone would like to comment/correct my findings, I am happily open to suggestions.

Thanks!

Cole

[wdelaney72]

(1) Dual 32uf @450v as per PDF or (1) Dual 20uf (as per Ralle Spec)

You could very easily take (2) single Axial Sprague 20uF (or BC) caps and wire them up like a dual can to keep the vintage filtering value. I know George specifically does this in his '67 build and I'm doing that in my current 12xxx build.

[Bainzy]

I personally like dual 16uF in the preamp can cap (where Ralle has dual 20uF) and two 32uF's in series on the screens (to make 16uF). Then for the Phase Inverter can (cap on top) I like dual 50uF, as it seems to sound more "rock"

[Mr G]

Having recently toy'd around a lot with all the different filtering values in several new and old marshall super leads, you will probably find that you will not hear any discernable difference between a 20uf cap, and a 33uf cap in either the PI stage of the amp or the power section filtering. If you can hear a difference, you should be working in the intelligence gathering station at GCHQ in th UK...they could do with a good pair of ears there!

Someone please correct me if i am wrong, but all that the caps are supposed to do in an amp is maintain a constant sin wave of voltage when you are playing - to make up for the AC coming in from the mains...(so my dutch repair man keeps informing me when i do his head in with such questions) G-blift!

The higher the filtering, the better it manages to maintain a constant stream of voltage within the amp...which gives a tighter/cleaner sound/crisper bass response... although it doesent really ~change~ the sound so much as it helps eliminate other things...like oscillation, ghosting, background interference noises, muddy bass etc...so I am told... %-)

When I halved the value of my screen, main and PI caps...i could not tell any significant difference in the amp whatsoever except ithat it ~felt~ a tad softer in terms of the response...which was weird as i thought it would be like night and day...as opposed to twilight and dawn...

Play around with your chouices...dont be afraid to try something different...as this often leads to the more revealing and exciting things that set you apart from your peers... cool

[45auto]

I personally like dual 16uF in the preamp can cap (where Ralle has dual 20uF) and two 32uF's in series on the screens (to make 16uF). Then for the Phase Inverter can (cap on top) I like dual 50uF, as it seems to sound more "rock"

ditto bubba!

[rockstah]

F&T cans needed.

two dual 50u cans - jumpered to = 100u - in series is 50u on the mains

two dual 32u cans or two 33u axial cans ( close enough ) run in series to = 16u or 16.5u on the screens.

one dual 32u can for cap on top - only one side is used for 32u PI cap

one 32u dual axial can = preamp cap on main board

two BC 10u cans for your bias circuit

other electrolytics are two BC 330u caps for your cathode caps

filtering ( higher or lower) is not so much about how it sounds as it is to how it feels and responds.

[pongo316]

F&T cans needed.

two dual 50u cans - jumpered to = 100u - in series is 50u on the mains

two dual 32u cans or two 33u axial cans ( close enough ) run in series to = 16u or 16.5u on the screens.

one dual 32u can for cap on top - only one side is used for 32u PI cap

one 32u dual axial can = preamp cap on main board

two BC 10u cans for your bias circuit

other electrolytics are two BC 330u caps for your cathode caps

filtering ( higher or lower) is not so much about how it sounds as it is to how it feels and responds.

Thats what I'm going for

[mightymike]

I personally like dual 16uF in the preamp can cap (where Ralle has dual 20uF) and two 32uF's in series on the screens (to make 16uF). Then for the Phase Inverter can (cap on top) I like dual 50uF, as it seems to sound more "rock"

ditto bubba!

I have this same setup as well, but I'm tempted to try cutting or switching the jumper, and/or replacing the 50x2 with a 32x2 F&T, but it's much more fun to just play it.