Good Bias level for Jcm2000 Combo

LpPepper

Dropping my DSL401 into Jimi at Jimis music store in Ballymount . Getting TAD Ei EL84 valves in her .

What Bias setting should I tell him to put it at in terms of mV (i.e 45mV)

darrenw5094

LpPepper wrote: »

Dropping my DSL401 into Jimi at Jimis music store in Ballymount . Getting TAD Ei EL84 valves in her .

What Bias setting should I tell him to put it at in terms of mV (i.e 45mV)

Post it on here http://www.marshallforum.com/

Plate voltages would have to measured first and a fancy formula to calculate the bias. Heater voltage, blah, blah. I never got the time to go through the bias thing properly.

NeMiSiS

1.375v according to http://www.guitartricks.com/forum/archive/index.php/t-4771.html and a few other sites...

stephenshields2

NeMiSiS wrote: »

1.375v according to http://www.guitartricks.com/forum/archive/index.php/t-4771.html and a few other sites...

1.375 will blow the bollocks out of the poor thing.

I only did my JCM2000 TSL 100 the other day, and although Marshall recommend 90mV for my head, I biased it to 83mV, because I know that 90mV is too hot, and will burn out my valves quicker than they should.

LpPepper, do yourself a favour. Buy the valves yourself, and get somebody in the know to do the work.

You'll save a bunch of time and money. My local music shop was looking ~240 Euro for valve change (and **** valves) and I got very decent valves off the net for 128 Euro, and did the fitting and bias myself.

I still have never come across a music shop that I trust enough to do a valve fit and bias. Its such an important thing, you wanna make sure its done right!n:)

Paolo_M

stephenshields2 wrote: »

1.375 will blow the bollocks out of the poor thing.

I only did my JCM2000 TSL 100 the other day, and although Marshall recommend 90mV for my head, I biased it to 83mV, because I know that 90mV is too hot, and will burn out my valves quicker than they should.

LpPepper, do yourself a favour. Buy the valves yourself, and get somebody in the know to do the work.

You'll save a bunch of time and money. My local music shop was looking ~240 Euro for valve change (and **** valves) and I got very decent valves off the net for 128 Euro, and did the fitting and bias myself.

I still have never come across a music shop that I trust enough to do a valve fit and bias. Its such an important thing, you wanna make sure its done right!n:)

That would depending entirely upon the plate voltage that the amp was running at as well as the biasing method.

OP, I don't know this amp well enough to say what you should or shouldn't bias it at.

However I did take the time to look up the Marshall DSL401 user manual on-line from a google search.
It suggested 1.3 to 1.4Volts at the bias point. That translates to around 32mA - 35mA idle current per EL 84 valve, which would be about right assuming the plate voltage was around 300Vdc.
Keeping it in this zone also ensures that you are within Marshall specifications if there is an issue.