Isolating Capacitors
 

These little wonders just popped up a few days ago in Kevin's No. 11 Set thread I believe and they seem to have generated a lot of comments.

These items show up on a very regular basis it seems on eBay, nearly always ID'd as being a No. 19-Set item, sometimes the 22-Set, or less common, the 18-Set, and quite often flogged with horizontal aerials. Never seen them listed in any 19-Set manuals (standard sets at least), so other than the 19-Set HP, what other sets were they issued for as part of the kit?

Were these caps a standard size/shape and rating?

The intent for protection from overhead hydro lines strikes me as a bit odd. I have seen a number of photos of empty hydro poles and wall bracket insulators scattered all over Europe during the war, but cannot think of any photos I have seen with intact, operating lines. So now I am wondering if these isolating capacitors were a British interwar design, developed primarily to protect the wireless equipment in vehicles as they raced around the peacetime English countryside?

David

Here is one of a series of pictures I have, showing a WS 11 set up in a wartime PU. Ron

The capacitor is VAOS p/n ZA2060, X.5 5KV MK II. It was used with the British 19 set HP, the WS22 and the WS11.

These sets had no blocking capacitor in the aerial tuning system so an external one was supplied. I think Chris mentioned in another post that the regular 19 set variometer had the cap built in so you won't see it listed in a parts list.

The capacitor introduces a higher reactance (AC form of resistance) to the lower frequency ac supply. Capacitive reactance is the inverse of the frequency. In the radio freq range aerial current passes no problem but 50 or 60 Hz is greatly attenuated reducing risk of shock.

I knew all that :) Ron

It goes back to WW1, since the 1940 edition of the Z1 VAOS lists:

ZA.8486 (I think this is a mistake and it should be ZA.2060 because of the following two entries).

ZA.8486 CONDENSER, X.5, 5-kV., Mk. I ................each £ 0 8s 6d
.0005-uF.; 2,500-V., A.C., wkg.; wood case with ebonite cover; approx. 1.3/4-in x 2.1/2-in x 2-in.; fitted with 1 No. 2 B.A. terminal stem and 1 spring loaded insulated terminal; used with W.T. sets, MB/MC, complete stations, 1B and 1C when required.

ZA.2061 CONDENSER, X.5, 5-kV., Mk. I* ................each £ 0 8s 0d
.0005-uF.; 2,500-V., A.C., wkg.; wood case with ebonite cover; approx. 1.3/4-in x 2.1/2-in x 2-in.; fitted with 2 No. 4 B.A. terminal stem; used with Wireless. sets, No.2, complete stations, No. 2B and 2C; and Wireless sets, No. 7, complete stations, No. 7A

ZA.2062 CONDENSER, BOXES, CONTAINING

Ebonite; approx 3.1/8-in. x 3.3/8-in. x 4-in,; fitted with 1 terminal, brass, No. 2 B.A. on front; 1 terminal, spring, brass, special. with ebonite guard, 3-in. dia. on bottom and 1 M.S. plate with rubber washer to suit; used as aerial lead-in insulator on Tanks, light, Mks. II, IV and V; demands for replacements will state for which type of tank required.

... etc.

The "X.5" is the way the army used to specify condenser^W capacitor values; the letter is the multiplier and the figure(s) are the value. A subsequent letter identified the type /style - there is no rhyme nor reason to this scheme: letters were added as new components of that value came into service!

Multipliers:
No letter - it's the value in microfarads
P is .1 uF
Q is .01 uF
R is .001 uF
X is .0001 uF
Y is .00001 uF
Z is .000001 uF

Confused? You will be.