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Old 16th June 2009, 07:40 PM   #1
dogfish is offline dogfish  United States
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Default Adding panel meters to Simple SE?

Another silly n00b question.

I'm building a Simple SE, my first tube amp build. I think it'd be fun to have one or two panel meters on the front that react with the output level -- something really simple, some "idiot meters" (something for idiots to stare at).

Unfortunately my knowledge of electronics is sufficiently limited that I don't know whether I want an ammeter or a voltmeter, what scale I want, and where I can add it to the circuit without affecting the quality of the sound.

Can someone provide some guidance, either a simple solution ("wire a 10ma ammeter across R39"), or a pointer to what I should learn before I proceed ("get through the first six chapters of Horowitz and Hill and then ask again") -- or even "this is more complicated than you think, you should just focus on getting the Simple SE working")?

(On a related note, I'm thinking of putting a 6.3v pilot lamp in parallel with the heaters, i.e. across the T1-GRN connectors. Is this reasonable?)

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Old 16th June 2009, 08:39 PM   #2
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I asked a similar question a while back and was told to wire it into the output path to the speaker terminals. Not exactly sure how to implement, but I am sure someone will know.
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Old 16th June 2009, 08:39 PM   #3
rknize is offline rknize  United States
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Putting an ammeter in series with the power supply probably won't show much in a class-A SE amp. You probably want a volt meter. If you want to see the output, I think the scale needs to be on the order of a few volts... Just throw an analog meter on a speaker jack and see what you find.

You want the 6.3VAC indicator map on the heater winding...yes.
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Old 17th June 2009, 05:27 AM   #4
w5jag is offline w5jag  United States
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Go for the metering.

I have a 0-500ma ammeter in series with the choke in my Simple SE to keep track of power supply current.

I think metering is a worthwhile idea and even a series current meter in the PS output gives useful information. In a Simple SE about 20 ma of power supply current is for the 12AT7, and everything else is the output tubes.

I logged the loaded B+ output of my PS with various rectifiers and with this I can pretty much tell at a glance what the output tubes are doing at any given time.

I've seen gassy Russian 6P3-S tubes start to runaway on the meter, before any other signs of distress were apparent.

I have a 0-1ma meter that is shunted to read 0-100ma and can be switched to either tube to keep tabs on the output tubes in my Tubelab SE.

On my next Simple SE build, I'll probably meter each output tube individually in the cathode circuit.

Win W5JAG
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Old 17th June 2009, 08:16 AM   #5
595ss is offline 595ss  Sweden
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http://www.aha.nl/tubelevel.aspx

Why not do it with tubes?
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Old 17th June 2009, 04:13 PM   #6
dogfish is offline dogfish  United States
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Quote:
Originally posted by w5jag
I have a 0-500ma ammeter in series with the choke in my Simple SE to keep track of power supply current.

[...]

I have a 0-1ma meter that is shunted to read 0-100ma and can be switched to either tube to keep tabs on the output tubes in my Tubelab SE.

On my next Simple SE build, I'll probably meter each output tube individually in the cathode circuit.

Win W5JAG
Win - Thanks for the great information.

I understand "0-500 ammeter in series with the choke," but the other two are above my head. Can you take a minute to tell me where I would attach an ammeter to keep tabs on the output tubes? Will this supply the eye candy that I'm hoping for (meters that more or less react with the volume of sound coming from the speakers)?

(Given some time and some poking around I think I can figure out "0-1ma meter shunted to read 0-100ma" so I think I'm OK there.)

Thanks for patience with this n00b.
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Old 17th June 2009, 05:23 PM   #7
rknize is offline rknize  United States
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He's using them to check the bias current, so they are probably in series with the cathode resistors. They will sway a bit with the music, but I think what you are after is a VU/output power type of meter. For that, you want a volt meter in series with the input ("VU") or the output ("power"). Neither serves any practical purpose that I can think of, but they do cover the eye-candy appeal well (which I totally understand).

I would grab a trusty analog multi-meter (buy a super-cheap one from the hardware store if you don't have one) and plop it parallel with a speaker. Start with a high range as you would normally with a manually-ranged meter. You'll then know the voltages you are dealing with driving those speakers. Just note that they would be different driving speakers with a different impedance (4ohm vs 8ohm, etc). If you don't want to worry about that, go the VU-route (put the meter on the input).
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