Tube amp Bias

Midnite Mick

Can somebody give me little briefing on exactly what that is?

Is this something that is exclusive to SET's and doesn't apply to Push Pull. How does one know if it is required.

Also when they match them what does the Ip mean. Is there someacceptable tolerance?

Thanks,
Mike

PS. Some new tubes arrived today for me to play with JJ E34L's

candyliquor35m

Some amps are auto-biasing so no bias needed.

I just got my golden tube se-100 out of the shop to have the bias plate replaced. Occasionally it was causing a tube to die prematurely. On my model, the shop owner recommended a bias as low as .40 even though the manual recommends .48-52 so I went about .40

He said it extends the tube life and is easier on the amp. I can already tell the amp is running cooler if there is such a thing with tube amps.

Ricardo

Lower bias will extend the life of the tubes, but in my limited experience amps sound better if you run them hotter. Your choice

RuSsMaN

Lower bias makes the tubes run 'hotter'. You guys are thinking of it backwards - Bias is the negative voltage applied to a tube's control grid which allows the tube to stay within its operational parameters for your specific amplifier.

Too much bias, the amp will sound like crap. Too little, tubes can overheat and fail, taking output transformers and other parts in the circuit with them.

Cheers,
Russ

candyliquor35m

RuSsMaN wrote: »

Lower bias makes the tubes run 'hotter'. You guys are thinking of it backwards - Bias is the negative voltage applied to a tube's control grid which allows the tube to stay within its operational parameters for your specific amplifier.

Too much bias, the amp will sound like crap. Too little, tubes can overheat and fail, taking output transformers and other parts in the circuit with them.

Cheers,
Russ

I thought I remember reading you set yours on the low end of the range or just under the low end. So you think .40 is too low for a .48-.52 range? The shop owner was saying something about it depends on the amp and how much voltage is being supplied to or by the bias plate or something like that

RuSsMaN

I do, I like to live on by the seat of my pants, and I use only mil-spec power tubes - I like them on the ragged edge.

.48 to .52, I'd try and park it right .50 - especially with a GTA amp, which some of the best sounding, but prone to failure unless properly modified.

Cheers,
Russ

Schwingding

Read this:

http://www.tubedepot.com/whisbipo.html

candyliquor35m

I called the shop owner back and he said he measured the bias plate to be getting a reading of over 500 so then he computed the minimum bias for my amp at .40 ????

mhardy6647

Since electrons are negatively charged, they'll only flow towards a more positive potential. We think of music (a music waveform) as varying around zero volts, positive and negative. Well, all things being equal, a vacuum tube could only conduct, or amplify half of that waveform. Indeed, that's why the first tubes were diodes (rectifiers). Operating the tube at a bias lets both halves of an AC waveform be amplified (i.e., in a single-ended application) and the lets a tube operate in its linear range (for any application).

http://www.duncanamps.com/technical/ampclasses.html