In praise of lower-than-"optimal" biasing

[Jon Silberman]

I'd like to share a recent experience of mine with my Traynor YBA-1 that may perhaps be of interest to others with a variety of amps. The amp was running noisier than I had wanted with some hum so I brought it in to Pete Cage for a thorough review. Among his determinations was that the amp was biased way, way lower than optimal for the tubes in question so he installed an internal bias pot and cranked up the bias.

When I got the amp home and played it, it was not the same amp. Still sounded excellent but in a much more crunchy/Marshally way. The smoothness that I'd dug so much about the tone had been lost.

After some further discussion, I brought the amp back and Pete moved the bias pot to the external side of the back of the chassis. He then marked the "high" and "low" bias points of the pot with red and green sharpies, respectively to enable me, at home with a simple screwdriver twist, experiment safely with whatever bias points desired. We used the 21st century-unnecessary polarity switch hole for the pot so no drilling occurred.

I played the amp for a while still biased hot. Then, this morning, I lowered the bias back down to where it had been before. Wa-la: smoothness (and some of the hum, but ceis la vie) restored.

There's an ongoing DRRI thread describing how, while the amp allows biasing in the 22-25 ma ranged, folks like Mike Kropoktin (KCA NOS tubes) advise cooling it down to 18 ma, with most power tubes, for the best tone. This is sage advice!

http://pic20.picturetrail.com/VOL1600/682310/1133497/29560876.jpg
Note: Silberman faceplate installed for kicks using the preexisting Traynor faceplate screw holes. Original amp and faceplate unmolested.

[Axekisser]

That's interesting! I just recently raised the bias on my Princetons (Non verb and PR) from 18 to 20ma. I noticed an increase in low end and they seem firmer sounding. We'll see how they are live.

[phsyconoodler]

Good for you!You found a bias point that works with your tubes and your amp and how YOU play.Now get someone else to play it or change the tubes to a different brand,or try a different style of music.
We bias tubes for two reasons:
1) to make sure they don't melt down prematurely
2) for TONE
Tone is so many things to so many people,that nailing it down to 'colder bias' does not make any sense.

I bias for tone.Every amp and player and tube is different.
To say that amp A needs to be biased at 35ma and amp B needs to biased at 40ma is just plain silly.

If you like a DR biased at 18ma,then all the power to you!18ma saves the tubes,and hence KCA can warranty them easier.No failures means no warranty.

[stratman_el84]

There is no magical calculation or plate dissipation percentage that will give an 'optimum' bias setting. It varies with every amp and set of tubes, and also with every persons' taste.

I look up the maximum safe idle current for a given power tube, then I adjust the bias within that safe range while listening to the amp. The sound/feel of the amp will tell you when the tubes are happy.

Cheers!

Strat

[aleclee]

About 5 years ago, Scott Peterson came to the same conclusion with the 6CA7s in his Rivera Rake.

It's good to be reminded that "more" is not the same as "better". Running tubes at max "safe" bias doesn't necessarily translate to better tone or even "warmer" tone.

[phsyconoodler]

For HIM,that's the issue here.Bias the amp,experiment with the settings,and listen for the sound YOU want to hear.I can pretty much gurantee it won't be the same for everyone.

[Flyin' Brian]

To each his own and in this case I agree with the lower bias. One of the things that Mark Baier did at Victoria when he ventured into EL84 land with the Victorilux was to run the tubes at a much lower bias than everybody else was. The tone of that amp speaks for itself.
Jon next time you see Pete tell him I said hi. His little backstage amp KILLS.

[gldtp99]

Yes, i've always wondered why some insist running their output tubes at "70% plate dissipation" like it's some type of magic mantra----- if the amp sounds best there, no big deal-- but there's nothing wrong with finding out if a cooler bias sounds great in any individual amp----it's easier on the tubes, too................gldtp99

[Jon Silberman]

Thanks, guys.

Thought I'd add, I just PM'd Pete Cage this shortly ago which sums up my feelings at the moment:

>> My pleasure, Pete. Thought I'd add, just played the YBA-1 again this morning for an hour or so. It is now the equal of any amp I've ever owned or played. I could spend the rest of my life with just my Cage Bandmaster-alike and the YBA-1 and no other amps and be a happy man. Thanks again for everything. Jon Silberman