Swamper Resistors on 100 watt amps

[Structo]

I'm trying to educate myself about Marshall amps in preparation of building a kit or possibly going from scratch.
I've built a few amps but they have pretty much been in the Fender vein.

I am trying to wrap my brain around something I have noticed.

On the 60's 100 watt amps, the power tube grids are fed from the 220K splitters.
(the green and orange wires on most layouts)

I noticed on the Metro layouts there is it only one tube on each side that gets the 5K6 swamper resistor?

The wire goes to pin 5 where a 5K6 resistor then feeds the grid of the outside tubes.
But the two inside tubes appear to not have a grid resistor at all.

Yet the schematics of the 100 watters clearly show each power tube getting a 5K6 resistor on each grid.

The 50 watt layouts show each tube getting a 5K6 grid resistor.

Am I missing something here?

Can somebody help an old guy out here?

[Roe]

marshall didn't know what they were doing. each tube should have a 5k6-10k resistor

[Structo]

No, I'm talking about the Metro layouts.

I know some amps use the floating resistor (I think that's what it's called) before the swampers.
But not on the layouts I am talking about.

But on several Metro 100 watt layouts it shows one 5K6 for each pair.
The problem is, the way it is shown wired, only the two outside tubes are seeing the 5K6 resistor.

For example I attached a layout.

[paulster]

Metros are period correct, so they've replicated the same grid resistor 'error', if you want to call it that.

I always use one on each tube, but if you want to be period correct then you only use the two.

[Structo]

Thanks for the explanation.
I didn't know that.

Does just having them on two tubes create any instability?

I've looked over quite a few schematics at Schem Heaven and didn't notice that arrangement.
So possibly it was just when Marshall built the amps they skipped them.

What seems weird about that theory is that for sure they would notice the way they would have to wire the sockets to accommodate only one swamper to each pair.
It really couldn't be a cost cutting measure either since a resistor to them couldn't have cost a penny.

Unless they just liked the way it sounded that way better.
But according to most, you don't really hear swampers that much unless you go way small or way huge, like over 8K.

[flemingmras]

I asked this very same question to George back when I started building these things 5 years ago cause I had the same thought about the tubes that didn't see the resistor oscillating. He told me some early amps were done like that and in his experience he's never seen it cause a problem. But you can go either or.