I'm not sure I understand your question but I think the answer to your
question is option #1. That's because the circuit needs a low source
(power supply) impedance. I suspect your RFI is caused by parasitic
oscillations setup by the higher Ft of your replacement transistors.
Again, guessing, your replaced the old steel case TO3s with aluminum
case TO3s. One simple solution is to find some steel case BUX80s. If
they are not available you might try killing the oscillations with 100
pF caps from collector to ground. You may need to increase Rb on the
transistors too.
Fred Townsend
Declan Moriarty wrote:
I repair some Ultrasonic cleaners for the Jewellery trade.
/lead up
/Internal Description
These have a 220VAC mains input, bridge rec, 2 BUX 80s and a fairly big
ferrite transformer in the circuitry. The transformer is terrible. It
has 2 of those ferrite lumps from TV Line Output Tx and 2 coils, and is
held together by a tie-wrap :-/. Output is to 2 Coils mounted under the
base of the bath, which vibrate it.
/End Internal Description
I fixed this one, (replaced the 2 transistors) and it went back down the
country. It has come back because of radio interferance "It used not to
interfere with the radio before" I got manufacturer's replacements for
these transistors and tested it myself. On AM, the interference is
terrible, with a high spot around 550khz but it is very broadly spread,
and pretty dreadful. It's going out the input afaict. Moving the radio
off the same wall socket lessened it considerably. All the diodes are
original, although some dweeb may have switched _the radio_ from FM to
AM stations, as we have both. One of the top local stations broadcasts
still on 560khz.
/end lead up
Finally, the Question: How the hell do I set up the filter?
My first reaction was "Mains filter" but then they filter it from the
Mains side. I want to prevent the noise getting out, so I would prefer
option 2 below. But I'm not sure, so I'll ask you guys.
Option 1:
Mains-----Inductor----------------Bridge Rectifier
Capacitor
Mains-----Inductor----------------Bridge Rectifier
Or some other way, e.g.
Option 2:
Mains----------------Inductor------Bridge Rectifier
Capacitor
Mains----------------Inductor------Bridge Rectifier
--
Author: Fred Townsend
INET: [EMAIL PROTECTED]
Fat City Hosting, San Diego, California -- http://www.fatcity.com
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