[R-390] 26Z5W replacement

[Bernie Doran]

Normal arc suppression circuitry consisting of a cap and series resistor or 
just a MOV or both across the contacts should take care of any back EMF from 
the choke.   Assuming that is an issue and it could be.     A similar back 
EMF would appear across the SS diodes when turned off or to standby.  Yes, 
as long as somone is in there messing around including the standby would be 
interesting idea. I have not looked at the schematic, but it could be as 
simple as opening the time delay relay ground with the standby switch.   Of 
course the other factor is, is any of this really necessary, or is it simply 
a matter of thinking we can do a better job of engineering  than Collins 
did.   When I say we, I mean everyone else, because I can always improve 
things I have!!!   I even have the dead stuff around that I improved.  HI 
HI. excuse the HI Hi, just want to be sure everyone knows I am joking.

 I have open relays on my plate transformers and while that is AC there is a 
lot more current there, and I do not bother with any arc supression.  If 
opened at the right, or perhaps wrong time, there is a significient  flash. 
Arc supression should also be across mod transformers, and that is one of my 
IMPROVEMENTS that I have yet to do on my Gates BC1G. I have a few surge 
arrestors from the local power co, 15 KV and hundreds of amps. the 
construction certainly suggests that they have number of MOV disks in there 
and it should be easly to sort out the approate number of disks and clamp 
them between Lexan for a monster MOV.  only been waiting six years to do it. 
Bernie W8RPW
----- Original Message ----- 
From: "Charles Steinmetz" <csteinmetz at yandex.com>
To: "390 list" <r-390 at mailman.qth.net>
Sent: Tuesday, September 17, 2013 6:46 PM
Subject: Re: [R-390] 26Z5W replacement


> Bernie wrote:
>
>>If there really is a problem with the SS rectifiers, just use a time delay 
>>relay after the rectifiers to hold the circuit open for a minute or so
>>      *   *   *
>>The relays would likely be somewhat over spec with the B+ voltage, but I 
>>doubt if that would be an issue
>
> The relay would be looking into a big honking choke (2-12 H swinging).  It 
> would take a very specialized relay to interrupt that circuit (which would 
> happen at each power-down, power outage, and when switching into Standby 
> if one did it right and included Standby in the scheme).  Not impossible, 
> but not trivial, either.  And a bit of a kludge, IMO.
>
> Best regards,
>
> Charles
>
>
>
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