The AM Forum

I brought home a Collins 20V in December and have been getting ready to put it back on the air.
Not much in the way of info from it's previous life except that it was well cared for.
After putting Power on the box yesterday and discovering that it took out he 30 amp Dryer breakers when
HV was applied I started troubleshooting this morning.

I found a bad feed through for one of the plate connectors for one of the 4-400A's in the modulator.
It was perfect looking on top of the chassis but underneath was a disaster.

Could anyone steer me on to a place where I could get something that would work?
I took some pix that might help with size identification.

Pete

ebay, ham fests, or asking someone here.

I would go larger if one failed.

When I built my big rig a long time ago, I had a feed through between cabinets fail after a short time and replaced them with ones like in your picture, 2x as thick as original.
No problems for the last 30 years.

Replace both and go one size up.

Feed-thrus look pretty, but they can be a bitch to troubleshoot if they are barely arcing. How do we know unless we pull them apart to see the carbon tracks?

Instead, for DC and audio frequencies, I always use a grommet and pass good quality high voltage wire thru.  (and tall stand-offs with short screws so they cannot arc thru the inside)   This we can inspect and see in an instant if there is a problem.  

Yours were handling audio... but for RF, we need to use more care all around to prevent arcing. BIG feed-thrus may be the only solution for RF, or use a big hole..   I have arced over HV wire and grommets with RF several times.

Looks like moisture got into yours, yet another problem with them..

I have had at least six of those ceramics fail over the years and unless they blew apart, they were hair-pullers to find.

The other alternative may be to do as already suggested - get BIGGER ones.

T

There may be enough room for a Teflon sleeve and undersized stud. Maybe metric.

Definitely dissimilar half cell corrosion abetted by E. Current. Interesting how much of the the threads and metal has been eaten away.  Might look for more of the same and research why such a well cared for rig may not be so pristine elsewhere. 

The insulators on the back of a J. matchbox may be the right size.

quick search on epay:

http://www.ebay.com/itm/Ceramic-Feed-Through-High-Voltage-High-Current-Stainless-Hardware-/261409307908?pt=LH_DefaultDomain_0&hash=item3cdd357d04

Check the dimensions

Just a quick update on the 20V's operating condition.
I got a nice e mail from Gary, KG8LB offering to help me with the insulators.  
He whipped up two of these in his shop and sent them to me at no charge.
They work great.
What a guy.  
I've had the 20V playing into a dummy load for about 20 hours just to make sure it's
solid. 
A little over 600 watts output and nothing seems to be getting warm.
Working on a suitable antenna relay for this thing and should have it ready to go soon.

Pete

Last installment video of the 20V
https://www.youtube.com/watch?v=YycBDdKWDHM

Nice lathe work on the insulators.  What are they made of, nylon, Teflon??

Fred

For anyone needing old type porcelain insulators:  Daburn

http://www.daburn.com/10-58ceramicfeed-thruinsulators.aspx

http://www.daburn.com/insulators.aspx