Why are there extra caps on Marshall 1959?

[Rp3703]

I have a 1959 SLP reissue PCB that has extra capacitors added and I'm wondering if anyone has any idea why?
First, there is a 470p ceramic disc in parallel with the .0022 coupling cap off the bright gain stage
Second, there is a 1n ceramic disc running parallel with the 4n7 bright cap.
Third, there is a 120p ceramic disc running parallel to the 470p cap following the bright cap.

[SILVERGUN]

I'm going to go out on a limb here and say that there's only two logical possible reasons:
1- to acheive a very specific value that is not otherwise available in a single package
2- to benefit from the tonal character of 2 different cap materials

[Willabe]

I'm going to go out on a limb here and say that there's only two logical possible reasons:
1- to acheive a very specific value that is not otherwise available in a single package
2- to benefit from the tonal character of 2 different cap materials.

Agree with SG. 

Seems like the 1nF||4.7nF might be for getting 5.7nF? Same with the 120pF||470pF = 590pF?

And both of these might be cheaper for Marshall, if they keep them those 4 value caps in stock.

 

[shooter]

+1

I typically "tune" my amps that way, I start by "adding" cap, easy because you can just clip in || , IF that got me closer, I keep going, then solder in, leaving original.

IF I went the wrong way at 1st, I remove original, clip in something smaller and test
IF to far "the other way", clip something in || and re-test.

[Rp3703]

Even then, the combined values exceed the values listed on original schematics.

.0022uf listed / .0022uf + .00047uf = .00267uf
.005uf listed / .0047uf + .001uf = .0057uf
500p listed / 120p + 470p = 590p

Is it really possible to tell that a new 470p cap needs an extra 120p to sound like a vintage 500p?

[66Strat]

And both of these might be cheaper for Marshall, if they keep them those 4 value caps in stock.

 

Ding Ding Ding. We have a winner.

The purchasing department found a deal and the accounting department blessed the savings.

[Rp3703]

Saving what would amount to a dollar or two does not make sense on an amp that sold for around $2500 new. Fine tuning the voicing makes sense but if Marshall was trying to copy original specs to the T, does that mean that modern values are lower than vintage ones and it takes a higher value of capacitance to equal vintage values?

[Rp3703]

Another weird thing Marshall did was install 2K7/.68 on the V2's first cathode. I've only ever seen SLP's with either 1K or 820R on that cathode, not a cap resistor combo. Everything else looks stock.

[PRR]

> amp that sold for around $2500 new. ....if Marshall was trying to copy original specs to the T

Were they trying to copy?

Or were they just trying to get a piece of $2,500?

The larger caps make it brighter, makes it stand-out more on the showroom floor, makes the $2,500 easier to pay.

[66Strat]

Saving what would amount to a dollar or two does not make sense on an amp that sold for around $2500 new. Fine tuning the voicing makes sense but if Marshall was trying to copy original specs to the T, does that mean that modern values are lower than vintage ones and it takes a higher value of capacitance to equal vintage values?

That's not the way it works. Parts are not sourced per product. Parts are sourced to fulfill the parts needs for a product line. If for example a 590pf capacitor is unique to this amp and 120pf and 470pf capacitors are common to a variety of products, substantial savings could be obtained by buying the common parts in bulk to obtain a cheaper price and also to avoid the inventory expense of the unique parts.

Another weird thing Marshall did was install 2K7/.68 on the V2's first cathode. I've only ever seen SLP's with either 1K or 820R on that cathode, not a cap resistor combo. Everything else looks stock.

that was stock configuration for the 1959 MKII Super Lead.
https://drtube.com/schematics/marshall/1959mk2u.gif

[Rp3703]

66Strat, The schematic you posted has a 1K on the cathode of V2a, this reissue PCB has 2K7/.68 in that position. It also has the 2K7/.68 on V1b, which is stock.

[66Strat]

66Strat, The schematic you posted has a 1K on the cathode of V2a, this reissue PCB has 2K7/.68 in that position. It also has the 2K7/.68 on V1b, which is stock.

My bad. I overlooked the V2 part. Looking at the schematic that you posted, I don't see a 2K7/.68 combination. I see V1A - 820R/330u, V1B - 820R/.68u, V2A - 820R/.68. But then again, maybe I overlooked it. It has been known to happen.