Some years ago I received a phone call: “Hello. My friend says you’re an expert on setting up moving coil phono cartridges. I have a problem: when playing piano records, during crescendos there is distortion on one channel only.” This was any easy one. Many cartridge manufacturers are optimistic in their minimum tracking force ratings. I told this person that he should start from the beginning and set the tracking force 0.1 to 0.2 grams higher than the minimum, adjusting the anti-skate accordingly. He replied, “No. I think it’s cartridge loading.” Very unlikely. Cartridge loading affects transient and frequency response and to a lesser degree output. I explained that I was quite certain that what I was suggesting would fix the problem and that if it didn’t the cost of trying would be zero. Didn’t your friend say I was an expert?
He hung up.
Last week a man appeared at the door. He said he was having a problem with excessive plate current on his Dyna ST-70, a piece of equipment I am so familiar with that I can draw almost the entire schematic from memory. He kept insisting that the “bias” was too high. I told him he had insufficient bias. He replied “But the plate current is too high!” He has confused grid bias (often called bias for short) and the plate/cathode current that bias controls. He’s measuring the voltage across the 15.6 ohm cathode resistor that is brought out to the front-mounted octal test socket.
I received a follow-up email from him this morning saying “…it turns out bias level is not the problem…simply tested the bias range available without the power tubes installed…plenty of negative bias available.”
But he hasn’t actually tried it. He hasn’t tried it.
And if the bias voltage wasn’t a problem, the bias this morning is exactly what it was a week ago. If he puts the tubes in they will still have excessive plate current. This person simply does not understand that if everything is right with his ST-70 then the tubes he has are not good, and if the tubes are good there is something wrong with his ST-70. High plate current is a serious issue on any amp but particularly on amplifiers with smallish power supplies like ST-70’s. The transformers already run hot and the single GZ-34 rectifier is well stressed; the four EL-34’s alone take 200 ma of the GZ-34’s rated 250 ma.
And he absolutely refuses to supply any numbers as to what he feels is “plenty.” I’ve used more voltmeters more times than I’d like to remember and I’ve worked on thousands of pieces of gear. I’ve never seen a voltmeter with “plenty” on its scale. They have numbers. It’s numbers that make technical conversations possible and meaningful. (right : a typical analog meter that can be used to measure bias. Where’s the “plenty” indicator?)
Meaningful. That’s crux of the matter. People who call or stop by and play these games are not looking for meaning or a solution to a problem. They want to engage you. Ensnare you in their world. And it’s a topsy-turvy world. A world where everything is relative, there are no facts and no one knows more than anyone else. It’s also a world where they think I am supposed to have unlimited time to answer their psychological/spiritual/emotional problems disguised as technical queries. I am not supposed to get paid because according to them, my job is too much fun, and fun jobs don’t pay. Please don’t misunderstand. I love giving free technical advice as time permits but my requirement is that conversation is fruitful and enjoyable.