Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: plexi50 on March 05, 2012, 10:55:28 am
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I picked this up this morning from GoodWill here for $10.00. Is there any chance this can be use to measure the wattage of tube amplifier? Im a pac Rat and had to have it
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:thumbsup:
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Probably not. Google Weston 432.
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> use to measure the wattage of tube amplifier?
The AC wall-power IN TO the amp, yes.
I'd have to look-up if an AC Watt Meter accounts for reactive energy... however there is almost no reason a small power user needs to care.
It also has those exposed high-power connections, begging to hurt someone.
As for loudspeaker output.... well, it does go to 2.5KHz which is ample for guitar, but your 20V-30V signals are FAR below the nominal 115V (150V max) scaling, and the accuracy of these meters falls off badly at low voltages.
Power meters like this are for "unknown loads" (one lamp? three power saws?) and standard voltage (near 115V).
In audio it is much too easy and natural to use a Known Load (8.0 ohms) and a voltmeter.
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Well i suppose it just looks cool on the shelf.
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Without a doubt. Leave it out some where you and friends can see it.
Brad :icon_biggrin:
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Just hook it up to something and see if you can get movement. That would be cool.
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Just hook it up to something and see if you can get movement. That would be cool.
Now thats a cool idea. Tie it into my stereo system and see what happens. Could it handle Jeff Beck or Pat Travers?
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According to folks on the Antique Radio Forum, reactive loads will easily kill one of these meters.
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Looks like you can use it as safety device to monitor the current draw of an amp under test. I just bought a vintage AC ammeter for that purpose, to use in conjunction with a variac and an AC voltmeter. It's in a nearby thread. Your watt-meter will handle wall voltage of 120VAC @ 60 cycles. 5 amps of current draw will max it out at 600W. This should handle most amplifiers we work on.
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Can you tell me what terminals i am going to hook the 120V to? And where will the output to amp be?
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> reactive loads will easily kill one
I think that's an extreme which Plexi won't reach.
Hook up a pure 100uFd capacitor. This meter will show "zero" (real Power). But there is like 5 Amps flowing in the meter (out-of-phase with voltage, no real power). Carry this much further, the current-coil burns. But who has a 300uFd 120VAC capacitor?
I'll see if I can find my power meter textbook.
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Nice looking meter if all else fails
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In the old days you would have that thing converted to a Plexi by now! :icon_biggrin:
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Can you tell me what terminals i am going to hook the 120V to? And where will the output to amp be?
Best to get the manual if possible. However, looks to me like you can try a momentary test it with a 100W light bulb. 100W is good because it appears on the high and low scale, so you can test it with the Hi/Lo SW in either position. Seems that the hot (black wire) 120VAC should go to the 150V connection. Neutral (white wire) to the +/- connection; more specifically:
Hot VAC > momentary contact (can be done by hand, or with a momentary SW) > Bulb > 150V terminal; then +/- terminal > White VAC wire. With the connection ON, the bulb should light and the meter should read 100W on the scale selected by the Hi/Lo SW. If anything seems wrong, immediately cut the electrical connection.
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In the old days you would have that thing converted to a Plexi by now! :icon_biggrin:
Theres a first time for everything. The all new Plexston 1 Watt
Ive slowed down alot. A miniture bakelite plexi.
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Can you tell me what terminals i am going to hook the 120V to? And where will the output to amp be?
Best to get the manual if possible. However, looks to me like you can try a momentary test it with a 100W light bulb. 100W is good because it appears on the high and low scale, so you can test it with the Hi/Lo SW in either position. Seems that the hot (black wire) 120VAC should go to the 150V connection. Neutral (white wire) to the +/- connection; more specifically:
Hot VAC > momentary contact (can be done by hand, or with a momentary SW) > Bulb > 150V terminal; then +/- terminal > White VAC wire. With the connection ON, the bulb should light and the meter should read 100W on the scale selected by the Hi/Lo SW. If anything seems wrong, immediately cut the electrical connection.
Thanks for the info jjasilli . I will try it out tommorro and see if it works. It would be cool to see it work. I will use a alligator clip 5 amp circuit breaker that i built to complete the connection just in case anything goes wrong.
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Here's the basic hookup for single power/energy meters (attached).
The full load current goes through a very low-resistance coil. Probably your two big terminals, probably near 0.01 ohms. One of your wires goes through here.
The full load voltage goes through a high resistance coil (about 8K). We already have one side of the line, you need another terminal, it carries very low current, so this will be your small terminal. If you are in 120V land, use the 150V term.
If you are in a fight with the power company, it matters which side of the current coil the voltage coil connects to. (i.e. the meter eats some power, who pays for that?) In your case this is irrelevant; just mentioning so if you see it documented the other way, I'm wrong but it still works the same close-enuff.
I sure would start with a lamp limiter, and a lamp load. Start with 25W limit and 60W load. This won't light well or meter well but is safer than a large limiter and should budge the needle off zero.
When that seems fine, no-limiter plus a 100W lamp should read 100W, though I'm not clear what switch and scale to use/read. If you have a heater (not microwave) in the 600W-1000W zone, it should read nearly its nameplate rating. Any guitar amp smaller than a true SVT is within this meter's rating. A Champ should be 50W-60W steady, a 4-6L6 Twin should be 100W idle and 200W when lease-breaking. However the true current drawn is not exactly what this meter reads, there's some reactive current sloshing, so be generous when picking extension cords or fuses.
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Manuals:
http://www.amazon.com/Instructions-Weston-Portable-Wattmeter-Model/dp/B0064V5OSM (http://www.amazon.com/Instructions-Weston-Portable-Wattmeter-Model/dp/B0064V5OSM)
http://www.etestmanuals.com/Search.aspx?Mfg=WET&Page=3 (http://www.etestmanuals.com/Search.aspx?Mfg=WET&Page=3)
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Thanks much J&P. I looke all ove the internet yesterday and didnt find the manual or much info. I hooked the line load up to the 150V terminal yesterday and thats as far as i got before the phone and running around got in the way. Let me go check your info out and see if i can get this bulb to shine
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In the old days you would have that thing converted to a Plexi by now! :icon_biggrin:
Theres a first time for everything. The all new Plexston 1 Watt
Ive slowed down alot. A miniture bakelite plexi.
With a built-in output meter!!