Need pics of your ball spark-gap doohickies

[KK7UV]

I'm putting together the power supply of my own 813 rig build (finally!).   Can anyone supply some photos of their ball spark gap transient voltage suppressors you've mounted on your modulation transformer terminals?   I'd like to get a sense of needed size and construction technique.

Steve, KK7UV

[K1JJ]

Hi Steve,

A version of this homemade gap would work for you for an 813 rig.  Make it out of two insulator supported gap balls, (rounded nuts) like the ball on the right.  Using rounded balls as shown helps a lot for longevity and keeping the gap from burning down.  You only need to have one gap adjustable and then a nut to lock it down.

It should be adjustable without disturbing the wire connection as in this design.

Adjust it so that it will occasionally arc over when you hit the audio too hard. I have mine set so that they never arc unless I make a mistake. The audio compressor keeps it from getting into that area even if I scream into the mic.

A little trick:  Sometimes if the gap is not in plain sight it is hard to determine if it arced or it was something else in the rig. I put a 1" piece of scotch tape around the end of the gap ball (but not covering the gap itself) and it will melt after an arcover. In the initial stages of testing this can be a good checkpoint to know if the gap is coming on too easily or not at all.

T

[KK7UV]

Thanks a bunch Tom!  Looks easy enough.   
   

[w9jsw]

Hi Tom,

On my rig you stated I need 4 gaps. 2 on the mod primary and 1 on the secondary, and one on the mod reactor. Do these gap across the windings or do they gap to ground? I was thinking they gap across the windings and the spark gap base is fully insulated.

I am working on an alternate approach and just wanted to clarify.

I will post some pics tonight.

John

[K1JJ]

Hi John,

Yes, they go across the windings and are insulated from ground.  If you build TWO ball supports like the one pictured on the right, it will be what you need. Just make one adjustable, like the one on the left. (the one in his hand is grounded, thus no good)

There are countless ways to construct the gaps and some use heavy brass balls, but for your 813 rig the one pictured will get you by.

When I had some large commercial RCA mod iron (800 pounds for the mod xfmr) all of the iron had ball gaps.  They came stock on the mod iron pri and sec and also on the reactor winding, so I have always done the same here. For whatever reason I find that the primary gap on my 4-1000A rig is closer than the secondary gap to operate correctly. Just adjust all gaps so that they arc when needed as described earlier.

T

[w9jsw]

My concept for the mod primary gaps. Bought the clips on a 10 pack on the 'bay. Drilled a 3/16 hole thru on the side axis. Top screw fits nice and tight.

My plan is to mount the lexan sheet on the top of the mod trans at 4 corner holes. Maybe a lexan plate on top to cover it. That is the lexan part that is drilled for that mounting position. Thinking the ceramic pedestals can be shorter and the posts closer together. High HV leads come up from the trans posts to connect to the bases. I show welding rod wires but will change them to brass threaded screw stock that will have brass ball ends on them. Easy to adjust gaps and not all that ugly angle iron that I hear can be troublesome if it is zinc coated.

Second pic is the iron. The mod trans is in the lower center. The 3 white wires will connect to this pair of gaps. The 2 white wires are for the secondary gap. The lexan board will mount to the 4 holes on each corner of the mod trans. It is huge. The wires are 20kv rated wire.

Anyway, my design.

John

[W7TFO]

Basler and Electro Engineering use gaps only on the primary of modulation transformers.

73DG