The first 6A5G get*set*go is up!

2nd harmonics for the masses

Postby EWBrown » Wed Mar 26, 2008 5:57 am

Mechanical buzz is most likely caused by the power trannie or the choke, more so if the chassis is steel. Chokes, especially in a choke-input PSU can hum and buzz rather seriously.

I've run into various low priced power trannies, which hum, rattle, buzz,
and in some cases (like the infamous Hand Wound trannies), they can generate a sound like a cheap electric shaver :o Yellow_Light_Colorz_PDT_21

/ed B in NH
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It is the spec Hammond choke The power tran is a Trafomatic

Postby hembrook » Thu Mar 27, 2008 3:25 pm

I have a 10H choke from Japan (A Noguchi) I could swap in to check for that. I don't know what happens to the power supply if I go from 1.5H to 10H.
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Postby lth1 » Thu Mar 27, 2008 4:25 pm

I believe that you can just replace the choke with a 55 ohm resistor and then check for hum on your system.
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Well, a 55 Ohm resistor would be simpler. How many watts?

Postby hembrook » Fri Mar 28, 2008 12:43 am

What wattage rating on the resistor do I need? We are looking ar 300V across a 55 ohm resistor. The choke is rated for 150 mA. That is 45 watts, If I am understanding Mr. Ohm.
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Postby mesherm » Fri Mar 28, 2008 9:13 am

What wattage rating on the resistor do I need? We are looking ar 300V across a 55 ohm resistor. The choke is rated for 150 mA. That is 45 watts, If I am understanding Mr. Ohm.


P = I^2 * R so (.150)^2 * 55 = 1.24 watts
A 3 to 5 watt 50 to 55 ohm resistor should work fine


Power = volts x amps. You would need to measure the voltage drop ACROSS the choke not the voltage applied. I'm sure the voltage drop across the choke is not 300 volts . E=I*R so 0.15 * 55 would give a voltage drop of around 8.2 volts. Now when you calculate power you have 8.2v * 0.15a = 1.23 watts.
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Postby SDS-PAGE » Fri Mar 28, 2008 9:40 am

Could you also measure the voltage drop across the resistor then calculate the current accross it to get P=VI. Also, you would P*3 to get the safe wattage fo the resistor? Or am I totally dreaming?
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Postby mesherm » Fri Mar 28, 2008 10:39 am

Could you also measure the voltage drop across the resistor then calculate the current accross it to get P=VI.


Certainly you could. Current is usually a difficult property to measure in situ so measuring the voltage across it to get the current works fine.

Also, you would P*3 to get the safe wattage fo the resistor? Or am I totally dreaming?


Your not dreaming, normally I would use at least 3 times the calulated power dissipation to rate the resistor. In this case though it was only going to be in circuit temporarily so he could check hum.
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That's why I ask tese questions

Postby hembrook » Fri Mar 28, 2008 4:09 pm

You guys have a wealth of info, and frankly after a long LONG day and a glass of good German Dornfelder, I am not into math. Thanks!
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