[Amps] Amps Digest, Vol 51, Issue 41

[Garry]

> Date: Wed, 21 Mar 2007 12:32:17 -0400
> From: "Tom W8JI" <w8ji at w8ji.com>
> Subject: Re: [Amps] Surge resistor
> To: "Rick Stealey" <rstealey at hotmail.com>, <amps at contesting.com>
> Message-ID: <01b501c76bd6$92767a80$640fa8c0 at radioroom>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> 	reply-type=original
>
>   
> Now you have a .6 ohm resistor that we already know is useless because of arc path length) in series with the 50 ohm. All it does is add something to be a nuisance later on. It doesn't really protect or fuse anything, it's just something to replace later that really never helps.
>
> Why add a part that does nothing?
>
>   
>> can't see the value of the 50 watter.  In case of 
>> extremely high plate
>> current, such as hitting it with full drive and no load, 
>> say 2 amps of plate
>> current flows and even then the big resistor only drops 
>> 100 volts, and heats
>> up 200 watts. I wouldn't expect a wirewound power resistor 
>> to fail
>> immediately under these circumstances, and I can't see how 
>> it is protecting
>> anything.
>> What am I missing here?  Is the 50 watter the wrong type?
>>     
>
> It's for fault limiting. For plate current protection you 
> need a real fuse.
>
> 73 Tom 
>
>   
I have an L-4B and L-7. Both have the same HV supply which uses a 2-watt .82 ohm "fuse" resistor in series in the B+ line. I have often wondered why Drake did this rather than use a real fuse though the primary side of the transformer has breakers. There are 2 50K ohm 50-watt bleeders across the output but no "glitch" resistor. The bleeders cause the supply, which is outboard from the RF deck, to run hot to the touch. 

73, Garry - WR4R

>