Quick question on biasing Marshall Amp

[lovehifi]

Biasing my JVM410H. Question is the house AC changes when home lights, AC, appliances and anything else that draws AC current is on or off. Example if my TV and stereo are on the ma rating may be 30ma on a tube but when I turn off all AC loads that tube may jump to 36ma. Should I turn off all loads on the AC circuit I have the amp plugged into before biasing? Thanks

 

[ampmadscientist]

Biasing my JVM410H. Question is the house AC changes when home lights, AC, appliances and anything else that draws AC current is on or off. Example if my TV and stereo are on the ma rating may be 30ma on a tube but when I turn off all AC loads that tube may jump to 36ma. Should I turn off all loads on the AC circuit I have the amp plugged into before biasing? Thanks

Yes set it with the loads turned off.
Then it will never go higher than where you set it, only goes lower.

 

[MickeyJ]

it wont matter one bit.

tubes aren't cut daffodils that wilt in the sun.

 

[lovehifi]

Thanks guys. Wasn't sure. Have it all biased up and sounds great. Came from the factory biased pretty cold so I warmed her up a little. Amazing what a little bias adjustment can do to overall tone.

 

[Matthews Guitars]

If your house power changes that much with just a few appliances turned on or off, you'd better call an electrician to find out what's going on, and fix it, before you come home one day after work and discover this at the end of your driveway!

That is NOT normal!

 

[ampmadscientist]

Thanks guys. Wasn't sure. Have it all biased up and sounds great. Came from the factory biased pretty cold so I warmed her up a little. Amazing what a little bias adjustment can do to overall tone.

The problem could be up on the utility pole.
You can call the electric co and ask them to check the connections.

 

[Lance Chambers]

.....That is NOT normal!

Matt is correct! Your wall outlets should not fluctuate more than +/- 1% under load. Have it checked.

BTW! What was the factory setting on your amp? Mine (new 2018 model) was set at 34mA. I just left it as is.

 

[lovehifi]

Matt is correct! Your wall outlets should not fluctuate more than +/- 1% under load. Have it checked.

BTW! What was the factory setting on your amp? Mine (new 2018 model) was set at 34mA. I just left it as is.

My house wiring and current is fine. That was just an off the cuff example I used. When the AC is on along with a 70 inch TV, high power two channel stereo amp and other electronics I show about 2ma difference per side vs everything turn off. My 2018 410H was biased pretty hot on one side and pretty cold on the other. It was 78ma on one side and about 58 on the other. The tubes were matched okay. I ended up with about 69 and some change on each side.

 

[Matthews Guitars]

At what plate voltage? You have to take bias current AND plate voltage into account, you know.

 

[Gene Ballzz]

My question is: "how much difference there is at the wall outlet between your 30ma and 36ma readings." If you are expecting a direct correlation of current draw to wall voltage that would require a 20-ish% difference in wall voltage! I'm betting (or at least hoping, for your sake) that the wall doesn't fluctuate between 110VAC and 132VAC!

Just Sayin'
Gene

 

[South Park]

Things can get kind of wired on the power grid .

 

[MickeyJ]

south park imma call you 'spark' from now on.

 

[MickeyJ]

you guys know in the old days they didn't even bias their amps right? they just pulled the trashed ones out and put a new one in.
yeah the good old days.

 

[Chris-in-LA]

south park imma call you 'spark' from now on.

Not Sparky?

 

[MickeyJ]

yeah sparky is better.