Oil filled High Voltage Capacitors, ground the case?

[ND9B]

The high voltage filter capacitor (8uf 3000V oil filled can) on my Gates BC-1G transmitter is missing the clamps which hold it to the chassis. I used a little Mighty Putty around the base to at least keep it from sliding around. One of the terminals is grounded, but the "can" itself is floating. Should I clip a ground connection to the can? (I'm worried that a floating "can" may pick up some potential and might even arc to ground.)

In general, should the cases of oil filled capacitors be grounded?

Bobby Dipole, ND9B

[W7TFO]

Yep, they were meant to be grounded.

If you can't source the brackets, a couple pieces of all-thread can make some pretty good hooks to hold them down.

73DG

[WQ9E]

Like TFO stated, clamp it so that it is both mechanically secure and grounded.

For safety reasons anything that was meant to be grounded should be grounded so that you or a future owner doesn't receive a serious or fatal surprise.  This is why I don't like the hammy practice of floating leaky chokes (like those in some production runs of SP-600 receivers) above ground.

[KA3EKH]

Back in the old days when there use to be more tube AM broadcast transmitters and little one owner station (cheap) was a common sight to see in the old gates or RCA transmitters the modulation transformers and power supply chokes unbolted and sitting on blocks of wood because they had insulation breakdown. I never liked the looks of that but these were owner operators who the annual replacement cost of tubes was an issue for so no way they would want to spend money on a new transformer when you can rig it. Remember one station WKEN that was so cheap that when they needed to get a new set of modulator tubes for their transmitter they tried to act like no one was in the building when they were delivered in the hope that the delivery company would leave the tubes there and then tried to get out of the bill by saying they never received them.

[W1RKW]

nothing wrong with floating them as long as you provide a large and visible warning tags or provide sufficient encased protection. I've floated some HV stuff in my rig just to protect it because its pretty much unobtanium but got warning tags all over the place.  Labeling stuff is good  practice even if it's not dangerous.  I'd never stick my hand in a hot rig anyway just because. Learned my lesson the hard way  and there are no 2nd chances.

[Jim, W5JO]

I wish MFJ would buy the amateur radio part of Peter Dahl.  Martin has a way of making money and selling parts that Amateurs need.  Harbach must be getting greedy.

[W7TFO]

MFJ makes nothing suitable for the long run today, I don't see why they would change the business plan now.

To the "floater":

"Ah so, you funny guy, we kill you last!"

73DG

[Edward Cain]

   Please forgive my ignorance, but where and how does the danger arise when floating a choke? I ask because I have been thinking about doing this with a power supply I'm building.

Thanks,
Ed

[W7TFO]

If you are building with tubes & HV, look back to the days of yore when it was well thought out and built to last.

Those caps were meant to be grounded via their metal case, and were designed to 'stand the gaff', as it was a point of sureness when they were used in that manner. 

If left to float, an internal short to the case would go unnoticed, and manifest in total failure later down the road, i.e...Headache things like RF pickup, changes in circuit value due to humidity, vibration-related intermittents, dust & crap causing a short out if the case was already hot, eTc. 

If things went to ground, you knew you had a problem with that cap now, not later.

If you want to 'float' the filter caps, buy the newer plastic encased jobs and be done with it.

73DG

[KA2DZT]

   Please forgive my ignorance, but where and how does the danger arise when floating a choke? I ask because I have been thinking about doing this with a power supply I'm building.

Thanks,
Ed

Because the choke can become somewhat leaky to the case.  This can put the full HV on the case.  Chokes and xfmrs can also build up static charges on them.

All your xfmrs, chokes and metal can oil caps should always be grounded.

Fred

[K5UJ]

yeah but what  if you are using a 60+ year old thordarson plate iron and the insulation may not be up to 4KV to the core.  otherwise it is a perfectly good transformer.  do you scrap it?

Jim, EPD and Heybour (sp?) in Michigan and Magcap are still around as far as I know.  EPD will make anything to your specifications.   Not cheap but copper has gone up.  Harbach was just a middleman between customer and Magcap.  Of course there's still hamfests and eBay and the for sale section here. 

[Opcom]

Everything has gone up. Harbach may be trying to survive with the higher cost of copper and steel and other things that may have gone up like compliance and government fees, whatever it might be. I wonder how much of that business is BC and ham transmitter parts and how much is new designs for other industries. He could always add a few high power output transformers to the list. No one makes an OPT for a pair of 811's at 250W, never mind a pait of 3-500Zs. I can see applying MFJ quality standards to the Dahl legacy. He'd spin in his grave.

[KA3EKH]

The day of high voltage low current transformers in broadcasting is done. Can not think of any of the broadcasters that I do work for using anything with tube outputs except as maybe backup transmitters and when they replace there current solid state transmitters those will be going. High power FM ranges of 10 kW or above people are still using tubes but that’s already going fast and cannot imagine anyone buying a tube transmitter today. With this in mind do not see any future in trying to sell custom built replacement transformers for tube applications in the broadcast industry.  I think that the only market for high voltage transformers, chokes and capacitors is in Ham radio or high end vacuum tube audio so you’re not going to see too many building just for those two markets. And if they did would assume that there is a larger vacuum tube audio market then the Ham market so we will see 6L6 and 6SN7 tubes along with plate and power transformers for them but not much else.
On the subject of insulation and HV back when I was working with analog television I was introduced to the Hi Pot tester. Its amazing the fun that can be had when you can develop 50 kV and try to get components to flash over and if you have to place your transformers or capacitors on something to prevent flash over cant you use something like lexan or PVC or anything except a chunk of wood that looks like you just pulled it out from the back wall?

[W2PFY]

Why not put a very high value resistor to ground on those "floating" components?

I had one choke that was leaking mounted on a flat piece of insulation material in a PS. I was able to pull a 30 foot arc off it so I put it in the negative lead or CT of the transformer. Problem solved for a PS problem.   

[Ralph W3GL]

I was able to pull a 30 foot arc off it

Wow Terry, 30 foot, sounds like a lightening bolt to me...   

But then, what do I know???

[John K5PRO]

Wow, 30 ft arc?

There are still a number of transformer manufacturers out there that can build HV magnetics besides the list posted here. For instance, Basler, SNC, American Magnetics, Stangenes, NWL are some that come to mind. They will all do small lots as well, but probably not 1 without a lot of money, as it costs to do the engineering first time.

Besides broadcasters using HV iron in older tube rigs, scientific and industrial RF will be using tubes for years to come, as the power levels, loading variations, and cost of replacement don't warrant switching to solid state at this time. With this, will come need for replacement transformers.

[Steve - K4HX]

The breakdown voltage of air is about 33 kV per cm or about 33 kv per foot.

A 30 foot arc would mean almost 1 MV!