1969 Marshall

[Valvehead]

I have a 69 Marshall 100w on the bench for a look over. Its serial is SL/A 7335A .

4 input / non master / EL34's

5 , 50/50 Erie filter caps

So, on 2 of the 50/50 filter caps towards the power section there are 2 , 2watt? resistors mounted to them , BUT , they are 47K.

Shouldnt these be 10k ??

Im not finding any 1959 model scems that show 47k there ?

[Enzo]

They should be whatever they are. The amp has gotten along with these resistors for almost 50 years. Seems pointless to decide they need changing at this point.

[m1989jmp]

These are for balance only, usually 56k, but value doesn't matter much. You're fine with 47k, just make sure they're within specs.

http://drtube.com/schematics/marshall/1959mk2u.gif

[J M Fahey]

And don´t go any lower.
10k resistors used as bleeders will smoke, glow dull red and burn in a couple minutes.

Obviously that dayb they had run out of 56k and 47k was close enough.
As Enzo says, leave as is.

[drewl]

The "magic" in why some Marshalls sound different!


They often used what they had lying around to fill orders.

[catalin gramada]

47k / 56k are also small draining a lot of current...but I just wonder now if are not choose it for this reason- draining fast with a rate to discharge to cut power grids before bias voltage goes to low when switch power off

[Enzo]

His resistors are not bleeders, he is referring to the dropping resistors between nodes.

[dstrat]

To clarify the node feeding the screens with 2 100-100 series caps usually did use 56k bleeders 1967 schematic used 32uf and do not show bleeders or balance resistors.
correction: 100-100 series caps for screens are on the 1970 schematic.

if they used 47k Juan most likely correct, used what they had at hand.

[dstrat]

I stand corrected, Enzo had it right according to this 1969 photo.

Marshall Model #1959 JMP Super Lead ? Amp Archives

[J M Fahey]

You are not talking about the same resistors

* Those wired *across* cap terminals (+ to - ) are bleeders, schematic value 56k, 47k is acceptable.
Not that large current consumption: around 5mA , and are dual purpose: equalize voltage across series capacitors and safety discharge them in a couple minutes.

* those separating caps , feeding different preamp stages (and phase inverter) are voltage droppers, typically 10k each, they also make an RC cell to filter ripple out.

They are not interchangeable, as I mentioned above 10k bleeders will overheat and burn, 56/47k droppers will drop too much, PI would still work but first preamp tubes could get as low as 90V or even less.

[Enzo]

I am yet to be dissuaded that whichever resistors he sees, he need not change them to different values from the ones that have worked for decades.

[Valvehead]

ok thanks

[Valvehead]

another oddity....there are 2 large metal caps , on the end of the board , power section. They dont appear to be polarized

they are labeled 0.25 uf / 600v , connected to the standby switch

i dont see these on any schematics

[g1]

The schematic from post #3 shows .22uF caps connected to the standby switch. (to the left of switch at HV winding)

[Valvehead]

Ok-- see them now..what is their purpose ?