|
Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
|
Thread Tools |
4th Aug 2004, 8:45 pm | #1 |
Retired Dormant Member
Join Date: Aug 2004
Posts: 4
|
Alignment AC/DC Chassis
Hi,
I want to align a Bush DAC10. I have an Advance sig. gen. The Bush has a live chasis and the generator is earthed. How do I get round this ?? Last edited by Darren-UK; 26th May 2007 at 12:52 pm. Reason: Subject clarified. |
4th Aug 2004, 8:53 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,947
|
Re: Alignment
The correct way is to use an isolation transformer and earth the chassis. The quick and dirty way is to use a suitably rated capacitor in the earth connection.
Make sure the chassis *isn't* live, i.e. is connected to mains neutral. HTH, Paul |
4th Aug 2004, 8:55 pm | #3 |
Retired Dormant Member
Join Date: Aug 2004
Posts: 4
|
Re: Alignment
Thanks Paul. I'll give it a go.
|
4th Aug 2004, 9:01 pm | #4 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,572
|
Re: Alignment
Hi st.mellion.
The correct way is to use an isolating transformer. this is the safest way to work on AC/DC chassis. However if you make sure that the chassis of the radio is definately connected to neutral (as it should be) then at a pinch you can disconnect the mains earth of the generator. This will at least ensure that when you connect the generator to the chassis of the set there will be no nasty bangs!! I suppose you could also use an isolating capacitor in the earth lead of the generator and retain the mains earth....something like a .01uF at 1000volts. I've never tried this though. Still emphasise that an isolating transformer is the only proper way. What do other forum members think? Rich.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
4th Aug 2004, 9:45 pm | #5 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,947
|
Re: Alignment
If you just want to do a simple RF/IF alignment you probably don't need to connect the generator to the radio chassis anyway. There'll be enough signal with just the signal probe connected.
As Richard says, an isolation transformer is always safer though. Best regards, Paul |
5th Aug 2004, 2:01 pm | #6 |
Rest in Peace
Join Date: Apr 2003
Location: Edgware, North London.
Posts: 307
|
Re: Alignment
If you do connect the sig.gen. to the chassis- not recommended anyway - but if you do, and you've carefully checked that the chassis is at neutral, then as a last check before actually making the connection just stick a meter between the generator earth and the chassis. It should read 2v- 3v ac.
With the best will in the world one can always make a mistake; if the meter reads 240v you can correct things before making it. Joe |
5th Aug 2004, 10:15 pm | #7 |
Heptode
Join Date: Feb 2003
Location: Garnant, near Ammanford, South Wales, UK.
Posts: 657
|
Re: Alignment
Hi all
If your house has an earth leakage trip, when you connect neautral to earth the 3 or 4 volt differance will be enough to trip the trip. Richard.
__________________
BVWS member. |
6th Aug 2004, 12:02 pm | #8 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,572
|
Re: Alignment
In which case it's probably better to use Pauls idea of 'loose coupling'. You should find that there is enough pick-up by just looping the generator output cable around the frequency changer valve making sure that the earth lead is insulated and well out of the way. For RF alignment you can place the output cable near the aerial rod (if it has one) or via a capacitor to the aerial socket (1000pF should be ok). If you connect the generator direct to the aerial socket it might cause too much damping and give poor results.
Rich.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
6th Aug 2004, 2:10 pm | #9 |
Retired Dormant Member
Join Date: Aug 2004
Posts: 4
|
Re: Alignment
Thanks to evryone for their advice. I feel much better informed and more confidant of approaching this now .....and more safely !!
|