question regarding B+ voltages and it's effect on the sound

[grindliner]

How does the B+ effect the final sound of an amp?

Example. I have a Jackson JG2 50w that I want to convert to a 50w plexi. My B+ is 400v, which is considerably less than that of a plexi.

I want to think that if I gut everything between the rectifier and the output section and replace all to plexi specs, that it will sound nothing like a 50w plexi.

Is my thinking correct on this?

[Structo]

Is that the actual B+ or Power tube plate voltage?

For instance on my D'Lite, the PT puts out 325v on the secondaries.
After the full wave rectifier I get around 435v on the 6L6 plates (x2).
So it really depends what kind of load you put on the transformer and how stiff the power supply is to what actual B+ you end up with.

I've seen guys multiply the secondary voltage by 1.4 to give a rough idea of what the B+ is.
In my case that comes out to be 455v which is a bit higher than reality.

If the amount of tubes in your Jackson are similar to what the tube load would be in the plexi, you should be ok.

For instance, the 2550 has a 345v secondary.

[grindliner]

With a wall voltage of 112v, my secondary is putting out 292v, at the first filter cap I have right around 408v.

Books I've read say to use 1.4 as a multiplier for a SS rectifier, slightly lower for tube rectifiers, like 1.1** to calculate B+.

[Structo]

Yes that sounds a bit low, I believe you want upwards of 500v on a Plexi.
Yes I did mean a SS rectifier.

Are you a member at the Metro forum?

Those guys know their Marshall's inside and out and you can find some voltage charts there or ask.

[M Fowler]

SS is 1.4
5Y3 is 1.13
5U4B is 1.2
GZ34 is 1.3

Rectified voltage from a bridge rectifier is 1.4, 1.13, 1.2 or 1.3 times the secondary.

[grindliner]

Yes I'm a member there too.

I guess what I'm asking is if I can use a plexi spec turret board in the amp at my existing voltages, and if I can, can I expect to sound decent, or should I just plan on adding caps to bring my voltages up.

[John_P_WI]

OK, I'm going to go out on a limb here BUT here it goes.

I think there is a little confusion here. Just adding caps won't raise the voltage, but it will affect the feel and tone. You will realize more change in tone with the way you set your pre amp / PI voltages and filtering than anything. Anyone who has played with Power scaling or VVR will tell you that just scaling the power tubes down 50 or 75 volts does not change the tone as much as changing the voltage on the pre amp.

400 v on the power tubes is fine. Sure to get the vintage tone vibe, higher voltages and lower filtering help, but I have built many a bassman / plexi's with 400 to 425 v on the plates and tweaked the filtering / neg feedback / pre amp voltages etc and they rock. You will lose some of the high headroom with the lower voltages, but who builds a plexi for sparkly cleans? You also don't have a 30 to 40 year old "Marshall" sourced OT in there either.

I guess the ultimate question is, what tone do you want? The guys over at metro certainly can help point you in a certain direction tone wise.

Good luck, John