[Collins] 30S-1 R205 replacement???

[Dr. Gerald N. Johnson]

An open bleeder will cause that voltage rise.

You have three such resistors in series, 18K each for a total of 54K. 
Changing one to 20K will change the string from a nominal 54K to 56K, 
less than a 4% change. Two 20K and a 15K will change the total nominal 
value to 55K less than a 2% change. In that situation the 15K will 
dissipate less power than the 20K resistors. With 3000 volts light or no 
load there will be 54.4 milliamps bleeder current. 20K will dissipate 
59.5 watts, 15K will dissipate 44 watts. Well below the 100 watt rating.

15k and 18K are standard RETMA 10 and 20% tolerance values. 20K is a 
RETMA 5% standard value but wire wound resistor makers have ignored 
those standards for most all history. Mil spec resistors would have 
followed the RETMA standard value series, hence 18K.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 8/29/2013 6:39 PM, frank hughes wrote:
> Hi,
> The plate voltage on my 30S-1 is running about 4200/SSB.
> I found R205 open (18k ohm, 100W Ohmite wirewound), I hope this is the
> cause.
>
> http://i180.photobucket.com/albums/x257/fish1_07/bridgeport/DSC0sdf0064_zpse38abb35.jpg
>
> Anyway, none of the usual sources have these.
> Mouser
> Digikey
> Alliedelec
> Newark
> ebay
> surplussalesneb
> fair
>
> I can get 15k 100W and 20K 100W, but 18 does not show up.
>
> The parts list says the tolerance is +/- 10%, so a 20K 100W is very close,
> would that be OK
> as a replacement?
> 73
> Frank
> KJ4OLL
> ______________________________________________________________
>