Diagnosis assistant

[R.G.]

Let's face it. This idea CAN actually be implemented. The questions are: will people pay for it, and what will they do with it?

I should be clear about this - yes, I think it can be done. I have no plans to try, for many of the tongue-in-cheek observations that have come up here, as well as others. I have no idea that it will replace techs, and a strong conviction that it should not and will not.

On the "pay for it?" front, the uC is about $2-3, the selector chips maybe $0.50 for a select one-of-eight, so there's a few of those, call it another $2.00. LCD display, $3.00. Bunch of resistors and caps, and a PCB. And a boatload of wires snaking out to all the tube terminals. Frankly, the parasitic capacitance of all those wires is likely the biggest operational problem.

"What will they do with it?" is a real, solid pertinent question.

Something like this *might* be useful to a touring pro for when the amp is suddenly not running right, but a hot spare is probably more immediately useful.

I was just fascinated at the idea, not voting for it becoming a standard. Nice pipe dream.

I can't help it. I can't make the ideas quit. -eek!-

[gmoon]

And all these guys worring about a tenth of a milliamp setting their bias, when I see on some schematics the bias setting spec was to monitor MAINS current and set the bias for X number of watts draw from the wall by the amp.


I used to have a 1982 Datsun 200SX, and one night about 2AM, in the middle of nothing, on the interstate, the CHECK ENGINE light comes on and glows at me. Oh my god!!! I had no idea, so I pulled over, couldn;t find anything wrong, car seemed to be running OK, so I gingerly continued on to my home. I'm no dummy, I had the service manual for the car. I got out the schematic for the car, and traced the light back to its control.

It seems the CHECK ENGINE light on that car was turned on by a switch on the odometer. I had just passed 50,000 milesw on the highway, and the little odo 50,000 mile switch turned on the light. A little research revealed the light was just a reminder to take the car in for its 50,000 mile checkup. The official procedure for turning out the light was in the manual too: remove the bulb. Sheesh...

Same experience with a GEO about 15 years ago. I, however, am a dummy--no service manual. And it was Xmas eve to boot, driving back from my inlaws...

[J M Fahey]

I guess all of you guys are missing the point.
Considering the new manufacturing/servicing trends, all the microprocessor has to do is:
1) Check its internal clock to see whether you *still* are under warranty.
2) Send an EMail to the Factory, to instruct them to send you a new one.
Its built-in GPS will transmit your actual position, anywhere in the World, so even if you are on tour they'll send the replacement where you exactly need it.
The Pro model even has advanced Artificial Intelligence algorithms to accurately guess where your *next* show will be, so you don't waste any second of your precious time.
3) After that, it detonates a small Nuke inside, to make sure it's not illegally .... grasp! ..... repaired
4) If you are *out* of warranty, it waits until you are real close to detonate, the World does not need any of you .... anticonsumers !!! yea, I said the word.

[Gtr_tech]

I think it would be great for a sort of "active protection" as well. You could put sense coils in the K circuits of the output tubes, monitor current and have a max I reference programmed in to the PIC. Put a relay in the B+ supply, and have that open up when the preset current is exceeded by X percent. Hey....while yer "in there" you could have an automatic standby-> play switching as well. Keep ppl from switching the amp to standby when its not needed.

[nashvillebill]

Don't forget the latest NFPA arc-flash requirements, folks...at work, anytime somebody opens a live electrical panel, they have to dress up in a "moon suit" and that's only at 480 volts...

can you imagine the OSHA regulators when they realize we're working on live circuits with voltages well over 500 volts (what's B+ on an old SVT?)

[Steve Conner]

Put a relay in the B+ supply, and have that open up when the preset current is exceeded by X percent.

I actually built that! Well, it sensed screen current and was supposed to save your power tubes if the speaker cable went open. But in practice it was an utter pain in the *** because now and then it would cut you off mid-solo.

That was when I realised that guitar amps are actually supposed to drive their tubes to destruction! And that latching protection is no good for musical instrument amps: you need clamping protection that can recover and keep the amp going. I ripped that circuit out and threw it in the trash.

Looking back, I realise part of the problem was that that amp had a 6.6k OT. The plates weren't very heavily loaded, so the screens would draw lots of current on audio peaks.