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Re: [Amps] open frame relay rating

To: <>
Subject: Re: [Amps] open frame relay rating
From: "Steve Flood" <>
Reply-to: Steve Flood <>
Date: Sat, 29 Mar 2008 12:31:29 -0600
List-post: <">>
Thanks Carl and others for the replies.  I don't plan to use this amp above 
20m actually.  One of my relays is very similar to the SB-220 relay - and 
thinking I'd use the same setup with a third pole for the bias circuit. 
BUT,  I surely do not want to lose any significant signal in RX mode.

Are the "general pupose" relays considered "open-frame" - I am referring to 
those where you can see the working parts through a clear plastic shell. 
They are used in my Amertiron remote coax switch and Ameritron rates those 
at 4kw HF.


> Many amps used open frame relays with 10-13A contacts and they worked well 
> at 1500W. The one issue with them is high VSWR in the thru position on 10M 
> which can fold back the power in a SS rig. The cure is simple, add a 
> capacitor from the thru loop to ground to tune out the Xl.
> You can use an adjustable mica trimmer and leave it or measure the value 
> and replace with a 1KV disc ceramic or 500V mica. Typical values are 25-35 
> pf. Any one will handle 100W with ease.
> Carl
> KM1H

>>I have several open-frame relays.  If I use one for the T/R relay, what 
>>should the contact rating be for a 1500w amp?   Is it as simple as 1500w / 
>>50 ohms = SQRT of 30A or 5.5 Amps?
>> Tnx,
>> Steve, KK7UV

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