Astron RS-35M Thumps when turned on

[KK7UV]

Not everytime, just occasionally.  Is it harmful?  How can I correct it?

[K8AC]

You can quiet it down a bit by putting something heavy on top of the Astron case.  The case is very thin steel and moves a bit in response to the rapidly expanding transformer field with the inrush current.  It's not harmful.  I stack another power supply on top of my Astron 35 and that pretty much solves the problem.  Also, I rarely bother turning off the Astron.

[KE4DRN]

hi,

I put a small amount of plumbers putty on top of
the transformer and then put the case back on.

The putty will fill the gap between the cover and the
transformer and any thump will be minimal.

you can also use a rubber eraser or some silicone sealer.

73 james

[KB3HG]

You could soft start the supply. similar to what is done on the big amps. A resistor in the power lead and a relay that closes momentarily after it is turned on. A RC network to a relay that shorts out the resistor so the primary does not get full voltage instantaneously when the power switch is thrown. It limits inrush through the switch and the transformer. Mine also thumps.

Tom Kb3hg

[WM9V]

God I wish I had a dime for everytime I had to come out to a house and
tell someone their Sony TV didn't have a problem and it couldn't be fixed.
Next time the Astron maakesd that noise, turn it off and on again .
 You will notice that the power supply doesn't make that noise.
Looking at a variac, you will notice the wall surge current on a discharged power supply
is quite high .
 The hopelessly stupid owners of high tech stuff are exhibiting a new form of hypochondria marked by hyper sensitivity towards anything they see, hear, smell or feel.
If the equipment has a fan,  all of the sudden they have hearing like a dog.
If  there is a noise they don't understand they will be able to hear it in the
next county .
Buy a new switching supply and sit there for the next year turning it on and off
waiting for a thump sound ...at least it'll give you something to do .

[KA5N]

My heart thumps when I am turned on.  Time is begining to take care of this problem as I don't
get turned on as often.

There is no problem.  You should have been around in the days when high level modulated AM rigs were the style.  Talk about thump!!!  You could identify the op by the sound his transformers made when he
hit the PPT switch.

Don't worry, be happy!
Allen

[KM3F]

The reason for the thump has been stated correctly.
What to do about it using a relay, it's contacts and a resistor and time constant delay will minimize the action to the point you would never hear it again.
I just built and installed such a circuit in a Linear amplifier by connecting in the HV transformer primary.
The relay is a 24 volt unit with 650 ohm winding.
Across the winding is a 600 mfd 50 volt electrolytic cap.
Connected across the power line after the power switch is a resistor string to drop the voltage to about 24 volts thru a diode to provide the relay with DC so it does not buzz at an AC rate.
When initial power is applied, the relay cap takes time to charge before the relay pulls up and shorts a 20 ohm 20 watt resistor allowing the filters to essentially charge full before the relay bypasses the series resistor and apply full line power to the HV transformer.
Initial turn on shows the plate voltage to slow rise to 2000 then jump to 2400 when the relay operates.
By adjusting the circuit values, this can be applied to just about any device that would benefit from inrush limiting.
Adjust the resistor string to closely match the relay design voltage used.
A slick deal.

[KM3F]

Here are the reasons why you hear the turn on action.
First, the power line is 60 hertz. The point in the cycle that you happen to turn the power off will magnetize the transformer core such that the transformer will present a very low impedance to the ac power next time it is turned on.
The next thing that gets into the act is the large filter capacitor also takes a huge amount of current to begin it's charge.
The last thing to happen is what you hear.
The transformer core acts like a big magnet during the inrush and pulls on the metal cabinet making the noise you hear.
So there are a number of things that go on to account for the next time the supply powered up.
It depend on where in the AC input cycle you turn off the power as to what happens the next time it is powered up, to hear the noise result.
For example if you happen to turn off the supply during the ac input crossover point (zero voltage) , you likely will not hear an inrush result the next time you powered up the supply.
Another example of this action is the old color TV sets had a metal mask behind the screen.
Often a service man would use a large coil to degauss the metal mask so the colors would be clean across the screen. If he would have shut off the coil close to the tube face it would alter the electron beam focus through the holes in the mask by magnetizing the mask when it should not be..
In your supply, turning off the power at any point other than the zero crossing point does the same action to the power transformer core.

[WA4HKY]

God I wish I had a dime for everytime I had to come out to a house and
tell someone their Sony TV didn't have a problem and it couldn't be fixed.
Next time the Astron maakesd that noise, turn it off and on again .
 You will notice that the power supply doesn't make that noise.
Looking at a variac, you will notice the wall surge current on a discharged power supply
is quite high .
 The hopelessly stupid owners of high tech stuff are exhibiting a new form of hypochondria marked by hyper sensitivity towards anything they see, hear, smell or feel.
If the equipment has a fan,  all of the sudden they have hearing like a dog.
If  there is a noise they don't understand they will be able to hear it in the
next county .
Buy a new switching supply and sit there for the next year turning it on and off
waiting for a thump sound ...at least it'll give you something to do .

That drivel was not necessary. Get a life, sir.

[W8JI]

Not everytime, just occasionally.  Is it harmful?  How can I correct it?

Understand what the noise is.....

The noise occurs because of flux leakage. When a transformer winding is delivering current, it generates a counter magneto motive force that opposes primary flux levels. This causes the impedance to drop and the primary draws more current to restore flux levels, but it also tends to push flux out of the core into the air. The flux pushed out into the air around the transformer can move other things, like steel covers.

This flux leakage occurs over a few cycles, not just one. Starting at zero does not fix it, it generally makes it worse. Starting on the declining edge of the top of the waveform is actually best, but still not a reliable fix because it generally involves a few cycles anyway.

The cure is to let the load slowly die off. This can be done by starting the primary through a resistance of a few ohms, perhaps a dozen ohms. The time delay can be extremely simple with only two components, a relay and a resistor.

You could get a 12 volt dc relay and connect it across the supply output, and have that relay short a 10-20 ohm 10 watt resistor in the primary, or you could get a 120 volt AC relay and have that relay coil across the transformer primary. Again it would short the series resistance in the mains but between the mains and the relay coil and primary.

The advantage of this system is it is "self-timing" and removes the resistor when the supply is nearly at full voltage (depending on the relay, at about 70% of full voltage). It requires no capacitors at all, and will work flawlessly. With a 12 volt supply you could copy what is done in the ALS1300 and even use the same parts, which is a 12V dc relay and resistor.

The thunk is probably not harmful, generally the only component being taxed is the off-on switch. In the Ameritron series of amplifiers I added step starts only to increase switch contact life and to reduce the PERCEPTION of a problem by customers. Measurements showed nothing else was unduly stressed by the inrush, not even filaments, but it did greatly improve contact life in the primary switching and got rid of acoustic noise.

Unless your Astron eats up power switches, I would probably leave it alone.

73 Tom

[KB9CRY]

Not everytime, just occasionally.  Is it harmful?  How can I correct it?

Don't turn it off.

[KH6DC]

To put things into perspective for you, my Astron RS-35M does exactly the same thing -thumps everytime I power it on and has been doing it since day #1.  Yes, I'm the original owner of this excellent power supply since I bought it from HRO back in 1994 and it still works great even with all those thumps.