Re: {Collins} Rebuild and modernization of the 516F-2 power supply



When you change out the selenium do you leave the 100 ohm in place?  
I am also curious if anyone has experienced collateral damage when the selenium has failed; if so what?  
Another point would be what happened first: the ‘collateral’ damage or the selenium failure?  Did anyone think about maybe a tube failure applied a lot of voltage to the grid circuit?
I have two round emblem 516F2s.  The older one has never had the case off since I’ve owned it.  I am in the process of taking it out of the case to see if the previous owner recapped it or not.  I think I will find it is all original; but,  we will see.
If someone has personally seen serious damage and can definitely attribute it to a power supply failure I will add a 0.5 amp fuse in the HV lead at a convenient point.  I think that would limit the damage no matter what causes a bias circuit failure. 
BTW I agree with Stanley that leaving the original tubes in place is far safer then changing to silicon diodes of any flavor for the high voltage circuits.

Best Regards,
KJ7NW

On Jun 12, 2014, at 9:49 PM, L L bahr via Collins <collins@xxxxxxxxxxxxx> wrote:

> Rush,  
> 
> Not sure which rectifier you are talking about.  There are three in all.  Two are tubes and one is a selenium rectifier.  You definetly need to change out the selenium.  Put a two terminal insulated terminal strip in there and hang your 1N4007 diode across the terminal strip.  Your 1N4007 diode will be a perfect choice.  (It can handle a lot more voltage and current then the original selenium rectifier.)  As for the tubes,  Who knows?  If they work, measure OK, they may last for a very long time.  I would not change them out just for drill.  (Some guys go crazy and install the 1N4007 diode inside a drilled out selenium rectifier block.  Your choice on that.  I'm kind of fussy, but not that fussy!  The 5R4 rectifier tube socket has been problematic for some.  Some think it's a good idea to replace the Collins mica based tube socket for the 5R4 tube with a ceramic socket.  This can't hurt but requires some digging as not every ceramic tube socket will fit into the existing hole
> .  In some cases the hole needs to be enlarged.  However, it is possible to find a ceramic tube socket to fit without reaming out the hole.  I bought some tube sockets that fit from Frank Krize in Naches Mississippi (K5SVC.) Frank sells tubes and other stuff on eBay.  He is a good guy.  I buy a lot of tubes from him.  His tube sockets come from China, but they fit and he carries them for Collins power supplies.  Take a good look at your 5R4 tube socket on top of and bottom of the chassis.  If you see any chips out of the insulator and especially if you see any of the exposed tube socket pins,  you might entertain the notion of changing out the socket.  When the tube socket arcs, it usually makes a carbon path at one of these exposed tube socket pins.  Since these power supplies are old, the tubes have been removed and plugged in again many times.  Over time, these chips start to form on the tube sockets.  I never noticed them myself until another ham made me aware of the pro
> blem so I started looking for the chipped out area and indeed I found them.
> Lee, w0vt  
> 
> 
> Hi List,
> This has been a great string as I'm in the process of recapping a 516F-2 as we speak.
> 
> My question is, should I replace the rectifier just for drill? And if so, will the 1N4007 (of which I have several) do
> the job? I'm short on knowledge of specs of solid state rectifiers (old vs new).
> 
> Rush WB6LXG
> 
> 
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