|
Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
|
Thread Tools |
5th Jan 2016, 11:41 am | #1 |
Retired Dormant Member
Join Date: Oct 2015
Location: Fenwick, Glasgow, UK.
Posts: 127
|
Homebrew R-C Bridge
Hello and Good Morning.
A few years ago I was given some items from a local hobbyist that he had been given from a deceased Radio Amateur. Over the holiday period I decided to sift through some of the items. I came across a neat little R-C bridge. It uses a VR130 ex government valve and just a few other components. The valve is an oscillator to drive phones. It originally was built in November 1947 but must have been modified later on for dry batteries. It came with a D cell dated 2005 which still was supplying 1.36v the two PP3 batteries were leaking. I replaced the PP3's and connected phones, within seconds the oscillator was running even though the 2v filament valve is under-run. I've checked the bridge with various resistors and capacitors and it seems spot on. Not bad for being homemade in 1947 and sitting redundant for a good few years. |
5th Jan 2016, 5:51 pm | #2 |
Octode
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,804
|
Re: Homebrew R-C Bridge
That's just lovely! It would make an ideal valve starter project for a newcomer to the hobby.
Neil
__________________
preserving the recent past, for the distant future. |
5th Jan 2016, 6:31 pm | #3 |
Octode
Join Date: Jul 2011
Location: Leicester, Leics. UK.
Posts: 1,681
|
Re: Homebrew R-C Bridge
Could it be this (with thanks to American Radio History and their search facility)?
Although the date is a puzzle, the article is December 1947 - unless your's was the prototype! |
5th Jan 2016, 6:39 pm | #4 |
Guest
Posts: n/a
|
Re: Homebrew R-C Bridge
Superb example of KISS (keep it simple stupid), I think you could make it an RLC bridge by adding a few inductors.
|
5th Jan 2016, 7:35 pm | #5 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,191
|
Re: Homebrew R-C Bridge
While you obviously can add 'reference' inductors, you can run in to two problems. One is that the inductance may depend on the current through them. The second is that they may magnetically couple to the component you are testing.
In general it is better to balance an R-L pair against a C-R pair, so you can actually use reference capacitors to measure inductance. A book like 'Measurements in Radio Engineering' (Terman) should explain this and also show how to add another variable resistor to be used to null out the resistance of the component under test. |
5th Jan 2016, 11:21 pm | #6 |
Heptode
Join Date: Oct 2008
Location: Aalborg, Denmark
Posts: 903
|
Re: Homebrew R-C Bridge
|
6th Jan 2016, 9:40 am | #7 |
Retired Dormant Member
Join Date: Oct 2015
Location: Fenwick, Glasgow, UK.
Posts: 127
|
Re: Homebrew R-C Bridge
Hello.
How very interesting. The bridge I have isn't missing the grid resistor as it is in the PW article. I believe that these items I was given came from a Mr Jackson, on the table a date in November 1947 pre-dates this to the PW article. Neil, I agree with you wholeheartedly, the bridge is an excellent little project for someone's first attempt using valves. |
6th Jan 2016, 10:02 am | #8 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,801
|
Re: Homebrew R-C Bridge
Bridges have been around a long time and with the components available in any era there may be completely independently made things which turn out to be quite similar. Or Mr Jackson could be the author of that article?
David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |