Kendrick Champ bias circuit

[The Dude]

It means I'm biting my lip trying not to say anything negative- in this case, anyway. A veiled Gerald Weber reference, if you will.

[Chuck H]

Sorry to ask, but what is the meaning of this taped mouth icon ? Tried to google it without success.

I think it basically means "Better not to say anything because it would surely offend someone." while at the same time implying that YES, you went there without openly admitting it

[pdf64]

I guess it’s akin to the saying ‘if you can’t say something nice / positive, don’t say anything’.
So if you’re bursting to contribute a ‘less than positive’ response, a taped up mouth may be necessary to comply with that

[loudthud]

There was one particular Guitar Show where Gerald was bragging (as he is prone to do) that you could stick anything in his Champ from a 6V6 to a 6550 and it worked just fine. No mention was made of adjusting the bias.

[uneumann]

.... you could stick anything in his Champ from a 6V6 to a 6550 and it worked just fine. No mention was made of adjusting the bias.

I recall the THD Univalve and Bivalve made similar claims - in fact they were marketed on the basis that almost any tubes could be used safely.
I still have my Uni. I used a 6550 and a KT88 in there for quite a while. I used a whole suite of different tubes in that amp.
It's just a simple cathode biased (bypassed) circuit with a bit beefier OT and PT (compared to the Champ).
My point is that it's not an unreasonable claim if the components are chosen accordingly. Perhaps Gerald used oversized PT/OT iron.
I'll accept that bias may not be optimal (centered) for all tubes, but the amp works and sounds pretty good over the 10+ yrs I've had it.

[Enzo]

It is just a guitar amp. FOlks often have the idea that bias is a super critical adjustment, but all you need to do is use a transformer good for the highest current, and a cathode resistor that is average for the range of tubes. SO some tubes run fairly hot and others fairly cold. They will all survive.

[Chuck H]

It is just a guitar amp. FOlks often have the idea that bias is a super critical adjustment, but all you need to do is use a transformer good for the highest current, and a cathode resistor that is average for the range of tubes. SO some tubes run fairly hot and others fairly cold. They will all survive.

I just wonder how that became a selling point. Anyone with some experience knows that there's an ideal bias point for a given tube type in a given circuit. It's the totally layman "tube rollers" that are attracted to such claims. This bodes poorly for the marketers of these products. They're selling the opportunity for the "tone" of different tubes without the possibility of actually realizing it. So now it's just a gimmick.

[g1]

And the tube rollers are typically the guys who want to nitpick over the tiniest subtleties of the sound. So for them, it's kind of funny to tolerate a compromise 'one size fits all' approach to the bias point.

[SoulFetish]

Cathode bias could also be made adjustable as below.

Dude, I dig this idea. This is a clever way of doing it sans negative supply. I wish I'd thought of it

[Enzo]

The problem as I see it is this: all these ideas like "optimal" are really part of the hifi world. SO a circuit is not optimal for a 6L6 when you cram a 6V6 into it or whatever, yet you may find it agreeable. The music world is full of stories like the guy who poked pencil holes all over his speaker cone to get a sound he liked. HArdly optimal. SOmeone decided on 70% at some point, yet Fender never launched tham that hot. And anyone working on 5150s knows that 15ma is common - 7 watts - at idle current.
I can line up a dozen octal power tubes, and try them out in the little amp. Maybe we don't get all the nuance, but we do get to hear differences where all the rest of the circuit is the same. SOmeone will find that appealing.

[uneumann]

^^^^^^^ If it sounds good and doesn't blow up, it's perfect.

Let's also be fair about the marketing in this business. Music companies need to sell gear so they all say and do whatever it takes to make the sale. If they're successful in the long run, it's probably not because of what they said to make the sale, but because their products sound good and hold up. I'd give anyone who can stay in this business for 10-20 yrs a lot of credit for that.

[Dave H]

This is a clever way of doing it sans negative supply.

It also works fine with the 680R replaced by a zener for adjustable fixed bias.