Phillips beehive capacitors

[VK4BXI]

Hi to the group,
I want to use some of the NOS Phillips beehive capacitors that I have available to me as part of the tuning for some 2 metre cavities that I am running up for the club (BARC). I have tried to find the data sheets on them to check Q and current ratings / voltage ratings etc. but with no success.
Please is there anyone out there who has data on these parts ?

Regards Bob VK4BXI

[VK3ZAZ]

My god beehives,
3-30PF design
2-10pf the other fwiw.
Unknown hm power
haven't seen or used one since home brewing in the 1970s.
Good luck

[VK4BXI]

Yes real history,
but we have the odd 100 or so. They can handle 350volts DC + depending on the type and are very nice to adjust and stable. So why not ?

[VK3MQ]

Hi Bob,

The bee hive trimmer is a great component that I have used many times in projects over the years. However be wary of their use in Hi Q cavity circuits because the R.F voltage may be in the order of thousands of volts even at moderate power levels.

A good stable capacitor capacitor can be manufactured from two disks of metal with a gap of perhaps 3mm. Looking at a bee hive trimmer now the gap appears to be a lot less than 0.5 mm.

Cheers,
Rob
VK3MQ

[VK3TU]

Yes real history,
but we have the odd 100 or so. They can handle 350volts DC + depending on the type and are very nice to adjust and stable. So why not ?

...because they're air variable capacitors and where you have air as a dielectric, you eventually get dust, dirt, moisture in there not to mention the remnants that creepy crawlies leave behind. I'd look for more suitable trimmers like Johanson porcelain types. These are much more stable and reliable in this sort of application, besides being very much more difficult to disturb accidentally. See my post on the cavities I rebuilt here: http://www.vklogger.com/forum/viewtopic ... 37&t=12900

[VK4BXI]

Thanks guys,
its nice to know there are some people who have been there and done it. Beehive caps for me are a "nice" mechanical design but not practical to manufacture in this day and age. I am busy "playing" with a selection of 4" 5" and 6" tanks with the intent of assembling a duplexer for our 2 Metre repeater. My intent is to put all tuning bits inside the tank to keep bugs and dust from having an effect on the tuning. Currently I have assembled a brass disk to replace one of the loops on a band pass cavity. I have fitted it with two TNC connectors and am working with various notch arrangements mounted on the inside (per some of the articles available on the net). So far I managed to replicate published results for a series tuned loop with the capacitor grounded but have issues with the return loss/SWR. I do have some of the porcelain plunger trimmers, one of which is on the test jig at the moment. I have a mini-vna to do the tuning, but never enough time to do all that I want to do.

Regards Bob

[VK3TU]

Time is always a problem when tinkering with these things, you can burn endless hours I know.

I like the beehive trimmers too for some applications, but I'm not sure I'd used them for this job. As I recall them, they came in two styles. One was a rough and ready solder in job with a wire helix as the centre post and the other was a much better quality design with a fine machine thread (BA?) post with a slotted tension band on the moving part. Most of these were screw-down types rather than solder-in types.

OK on the series tuned loops too. They work very well. The Telewave duplexer we use at RGL is built that way. It uses loops made from UT141 coax that are a hairpin shape about 150mm long and 25mm wide in 200mm dia. cavities. The centre of the coax is used as a DC shunt so that any lightning strike or DC potential on the feedline is shunted to ground. The outer of the coax is used as the L in the series tuned circuit. An elegant design.

...but have issues with the return loss/SWR.

Is the loop coupling adjustable on your cavities? Coupling will affect the return loss/SWR quite dramatically. I found this article: http://ve2azx.net/technical/ve2azx-duplexerinfo.pdf very useful when I was rebuilding our system.

[VK4WDM]

Beehive caps! Brings a sparkle to my old eyes! I have some mounted on a small board with pigtails and croc clips which I use for construction and repairs. They are very easy to adjust and once I have found the right value can be replaced with another permanent type.

Good luck with the cavities. The only cavities I worry about these days are not building them in my teeth

73

Wayne VK4WDM (but like beehive caps, still usable)

[VK3YE]

Also excellent for pedestrian mobile magnetic loops - at least for QRP



https://www.youtube.com/watch?v=kykqimN7nvI

[VK4WDM]

Hi Peter

Do you have a portable loop design for 40-20m?

73

Wayne VK4WDM

[VK2ZIW]

1st

Philips BeeHive trimmers come in two types:

1) TV and Radio, have a spiral wire and spring contact system.
2) VHF FM radio, have central fine threaded post and special nut. Silver plated.

Often, the values are written on them.

The Philips FM 1649 radios have them (type 2). Five in the Rx and 3+ in the Tx PA.
(Philips 1st fully solid state VHF FM taxi radio, circa 1965 possibly)

We have these trimmers in the BMARC 2m cavity set.