Need help on variable caps..

[wb1ead]

Hello all..it's project time here in moose country..I've got a slew of variable caps..most are I believe Hammarlund..I need the mf/pf capacities of these as well as the voltage rating too..yup I tried my best to look up this stuff but as usual I failed to turn up much at all..the numbers printed on them are as follows.........MC250M..MC50S..7581KS..there is also about 20 or so smaller ones with the KS numbers printed on them..if someone could tell me the specs that wud be great..or better yet a link/website that I could research the rest of the lot as the smaller versions that I didn't list here..many tnx to those that can help me   73 de DAVE

[KA2DZT]

MC250M probably a 250pf cap and other probably a 50pfd cap.  The KS numbers are probably Western Electric caps.

Fred

[aa5wg]

Here is a link to a slick L/C meter.

It saved me tons of time.

http://www.aade.com/lcmeter.htm

73,
Chuck

[Pete, WA2CWA]

Hello all..it's project time here in moose country..I've got a slew of variable caps..most are I believe Hammarlund..I need the mf/pf capacities of these as well as the voltage rating too..yup I tried my best to look up this stuff but as usual I failed to turn up much at all..the numbers printed on them are as follows.........MC250M..MC50S..7581KS..there is also about 20 or so smaller ones with the KS numbers printed on them..if someone could tell me the specs that wud be great..or better yet a link/website that I could research the rest of the lot as the smaller versions that I didn't list here..many tnx to those that can help me   73 de DAVE

Google found it quick:
http://cardwellcondenser.com/hammarlund-capacitor-division/

I should have the WECo info.

[wb1ead]

Tnx all..Pete that site answered a lot of the stash here..still a mystery for now on the ones marked with a KS either in front of the 4 numbers or at the tail end..they ARE marked Hammarlund on the ceramic part but no MC or similar markings..but based on the website you supplied Pete I should be able to identify them as they give physical size as well as number of plates..only have a few oddballs from other makes but they should be easy enough to figure out based on that site
               Thank you all for responding!   73 de DAVE

[AB2EZ]

The capacitance of a simple variable capacitor, having semi-circular rotor plates, is given by the following formula:

Fully meshed (maximum) capacitance (pF) =

8.854 x (2n) x (pi x r x r/2) / d

Where

n = the number of plates on the rotor or the stator, whichever is less.

2n= the number of pairs of facing rotor-stator plates. Each facing pair is a separate capacitor

r = the radius of a single rotor plate (in meters)

pi x r x r/2 = the area of one face of a rotor plate

d = the air gap between each rotor plate and the facing stator plate (in meters)

8.854pF per meter = the permittivity of air

Example 1

n= 8 stator plates
r= 0.05 meters (5cm) = approximately 2 inches
d= 0.0025 meters (0.25cm) = approximately 0.1 inches

C(maximum) = 222.5pF

Example 2 (see RF Parts company: 71-1-75-23 variable capacitor. Specified as: 14pF - 155pF)

n= 10 stator plates, 11 rotor plates
r= .0325 meters (3.25cm) = approximately 1.3 inches
d= 0.0019 meters (0.19cm) = approximately 0.075 inches

C(maximum) = 156.7pF


Stu

[Pete, WA2CWA]

Tnx all..Pete that site answered a lot of the stash here..still a mystery for now on the ones marked with a KS either in front of the 4 numbers or at the tail end..they ARE marked Hammarlund on the ceramic part but no MC or similar markings..but based on the website you supplied Pete I should be able to identify them as they give physical size as well as number of plates..only have a few oddballs from other makes but they should be easy enough to figure out based on that site
               Thank you all for responding!   73 de DAVE

If the part number is something like KS-xxxx or KSxxxx, they were most likely made by a commercial manufacturer to Western Electric specs. Tell me the number(s). My WECo capacitor book lists "all" of their coded capacitors made in house or by outside manufacturers.

[wb1ead]

Stu many tnx for the "formula"!..I promise ya I will attempt it..now Pete you asked and these guys are the last of the unknowns..I was able to find the rest using the Hammarlund specs you provided..haven't found what's left yet..??..here they are
                7581-KS no manufacturer found on these..notice the KS is after the 4 numbers
                 KS-7892  these are marked Hammarlund..notice the KS is on the front of the 4 numbers
                 ZR-15-AS  marked Cardwell
                 C135  marked OAK
                 488084-E  marked Tarzian
Again a big tnx for ur help and suggestions guys!..Pete if ya can't find the info I won't feel bad as probably 75% of them can be identified now..there's always Stu's formula if I need it..........73 de DAVE

[Pete, WA2CWA]

From ebay:
Cardwell ZR-15-AS variable capacitor, 1.5-15pF. Air gap .03"

[Pete, WA2CWA]

Third up from the bottom:

[wb1ead]

Jeez Pete you are da man!..that takes care of another bunch of them..just wish those KS-7581 were there..got a half dozen of those..not going to fret on the OAK or Tarzian ones as they do look like typical 15 PF jobs..if you do find the 7581 jobbys that wud be great!...thanks again Pete for scouting those out!   73 de DAVE

[Pete, WA2CWA]

Jeez Pete you are da man!..that takes care of another bunch of them..just wish those KS-7581 were there..got a half dozen of those..not going to fret on the OAK or Tarzian ones as they do look like typical 15 PF jobs..if you do find the 7581 jobbys that wud be great!...thanks again Pete for scouting those out!   73 de DAVE

I have no clue who made the 7581-KS caps. They're not WECo. Are they all marked the same way? All the OAK capacitor tooling now belongs to Cardwell.

[wb1ead]

Well Pete they are all marked the same..all 6..but I'm assuming since the other KS type were marked in black ink obviously by a machine printing system and appear as KS-7892 on the end stationary plate..these are marked also by a machine on the stationary end plates just as I described..the top end plate has the number 7581 and the bottom end plate has the KS marking..so I assumed maybe wrong that it wud have been like the others only in reverse..the only thing missing wud be the hash mark between KS and the number..there are 14 stationary plates and 13 movable ones able to turn 360 degrees by means of a screwdriver..to my eyes it looks a lot like a minature BC type of variable with the exception of being totally movable 360 degrees
                Maybe a pic wud help but that technology is not gonna happen here at this shack..sorry bout that..I'll just have to use Stu's formula and hope for the best...agn tnx Pete!    73 de DAVE