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Author Topic: Noisy tank...  (Read 3448 times)
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K8DI
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« on: October 22, 2020, 05:38:05 PM »

Working on getting an old linear amp going. Applied filament power today, finally, all seems good...except that also means the blower. Air noise is acceptable, motor hum tolerable...but that motor hum vibrates the tank coils which rattles noisily on its form. The coil is flat wire on some sort of grooved former. Any ideas on how to shut the thing up? Glue? Foam?

Ed

PS picture is as received...I HAVE cleaned it up some;-)


* 375C2CA0-D2A3-4524-9791-8E1237428A79.jpeg (329.13 KB, 1280x958 - viewed 323 times.)
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Ed, K8DI, warming the air with RF, and working on lighting the shack with thoriated tungsten and mercury vapor...
W1RKW
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« Reply #1 on: October 22, 2020, 05:58:59 PM »

looking at the picture and considering the amount of crud on the outside of the blower, I'd suspect that the blower internals might be just as cruddy if not worse causing an imbalance of the internal fan/squirrel cage and causing vibration. I'd pull the blower out and make sure the blower internals are clean.  Might as well disassemble the motor and lube the motor too. The motor oil port looks like it has its share of crud on it too. 
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Bob
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His fear was when I turned it on for the first time life on earth would come to a stand still.
Detroit47
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« Reply #2 on: October 22, 2020, 08:19:06 PM »

Epoxy
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K8DI
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« Reply #3 on: October 23, 2020, 07:12:08 AM »

looking at the picture and considering the amount of crud on the outside of the blower, I'd suspect that the blower internals might be just as cruddy if not worse causing an imbalance of the internal fan/squirrel cage and causing vibration.
There was a ton of hardened dust in the blower wheel. I’d already cleaned it out with compressed air and a toothbrush, the wheel is clear and the motor lubed up, before I ever powered it up. This picture was what it looked like before, it was handy to show the coil, but isn’t what it looks like now...

A previous owner had replaced the stock umbilical cable with a large C-J connector, including the 3kV B+, which in stock form was on a Miilen connector. I’ve put a plate over the hole with an SHC connector, a Powercon ac inlet, and a third connector to my home brew power supply to activate the relay that powers it up. I also replaced the rca input with a BNC, and the beatup SO 239 output with an N connector. The metering resistors were mostly replaced as well. The whole thing was in much worse shape than I thought, I paid too much, but, as the say, in for a penny, in for a pound, so it’s now just about ready for rf.

But back to the noise:
The level of vibration is higher that it should be but it isn’t imbalance from dirt, it’s more like 60Hz hum. The motor runs hotter than I’d expect, too. Do these blowers have a capacitor in them?

Ed
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Ed, K8DI, warming the air with RF, and working on lighting the shack with thoriated tungsten and mercury vapor...
W1RKW
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« Reply #4 on: October 23, 2020, 04:03:11 PM »

Hi Ed,
not sure if that is a similar blower I had, but it certainly looks like it.  I never figured out what the failure mode was but I could not get it to run right no matter what I did.  It would take 30 or more seconds to come up to speed no matter how I lubed it. And it ran hot once it got to speed too. I ditched it. it was a typical induction type motor, no capacitor in it, for what it's worth. I don't remember the specifics because it was a long time ago.
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Bob
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Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
KD6VXI
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« Reply #5 on: October 23, 2020, 04:14:42 PM »

Bad bearings.  Bad enough to cause drag and make it run warm?


--Shane
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K8DI
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« Reply #6 on: October 23, 2020, 05:03:08 PM »

Couple more pictures, better view of tank coil.

How bright are these supposed to glow? The glowing picture is 2500v/100mA, idling no signal, which the manual says is expected current when not in standby and no signal conditions.

Ed



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* image0.jpeg (601.49 KB, 2016x1512 - viewed 277 times.)

* image1.jpeg (509.31 KB, 2016x1512 - viewed 244 times.)
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Ed, K8DI, warming the air with RF, and working on lighting the shack with thoriated tungsten and mercury vapor...
KD6VXI
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« Reply #7 on: October 23, 2020, 05:33:55 PM »

That's 250 watts of idle.  I like running my 500Z tubes at 50 mils at idle.  Especially on AM.  But I also run 500 or more volts above what you are running.  At 3.3 kv and 50 mils on key down no signal, when I would drop to 2200 volts it would drop quite a bit.

--Shane
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km6sn
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« Reply #8 on: October 23, 2020, 05:39:44 PM »

Check your filament voltage. Older transformers were designed to supply
correct filament volts when  105-110  volts were applied to the primaries.
Modern line voltages are much higher.
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VE7RF
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« Reply #9 on: October 25, 2020, 11:45:49 AM »

Who made the amp ?   Looks robust for a  single  3-500Z  amp.

Jim  VE7RF
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