Yet another biasing question.

[Jerry G]

First of all I would like thank all of the posters here for the valueble knowledge I have gained from reading the posts here.

Now as far as biasing tubes is concerned, I know if not biased corrcectly you can damage the tubes but can you hurt other parts of the amp as well?

[Structo]

I suppose it's possible but it shouldn't really happen if you adjust the bias carefully at the first full power up.
Remember new tubes can drift a bit after a few hours.
So it's a good idea to check the bias after a couple hours then at around 6 hours just to be safe.

[Jerry G]

Thanks ffor answering, the reason I ask is I have a friend who changes tubes all the time and never biases.

Not only different tubes but switching El34's with 6550's and so on, and he never seems hurt anything.

[demonufo]

Well, switching to 6550's from EL34's should leave them biased very cold anyway, so that's not gonna hurt, just sound crap compared to their full glorious potential.
What would be a problem is in switching to 6V6's, which would then be biased waaaay hot.
Of course, this is assuming that the amp was previously correctly set for EL34's. If it was originally set for 6550's then trouble could be just around the corner potentially.

[Structo]

Well your friend has been very lucky.
Unless he is using a cathode biased amp he is playing Russian Roulette by not biasing.
No offense to the friend but he is probably ignorant about how to properly set the bias so he just plugs and plays.

As demonufo stated, some tubes are similar in specs so it may not damage anything to try them without biasing but other tubes could potentially cause serious damage.

I would rather know exactly where my amp is biased.
You can also pick the setting that sounds the best.
There is usually around 10ma-12ma difference between the max 70% bias and the low 50% bias that you can play with to find what is right for your amp and speakers.

I have an amp now that uses two 6L6's and the plate voltage is around 435v.
70% for that amp would be around 40ma and the cold side would be 30ma.
I experimented with it and it sounds best at 35ma which is around 60% for that amp.
The nice side benefit is that my tubes will last longer since they are biased a little colder.
Some amps sound better on the hot side.

You just have to use your ears.
If you are a gigging guitarist, then you need to turn the volume up to your normal level when playing out and listen to it after biasing. You will find a setting that simply sounds best, with the right amount of crunch and or clean you are after.
So the setting isn't really etched into stone, but rather one that sounds the best within those to max and min settings.
Hope this helps.

[Jerry G]

Thank you for the explanation.

BTW, the amps he is playing with are both Marshalls.

One is a 100w plexi reissue for the early 80's and the other is a 50w mk2 from a similar time period.