[TenTec] Fast Relays

[JAMES HANLON]

Folks,
 
For a fast-acting relay, you might want to consider a Mercury Wetted type.  The Western Electric 275 and 276 relays have a switching time around 1 millisecond and they have zero bounce on either make or break.  They are rated to switch and to carry 5 amps in telephone service.  I use one to switch the antenna in my CW QSK setup with a Heathkit SB-200 amplifier putting out about 600 watts into my 50 ohm load - that's about three and a half amps through the relay.  I have the relay and the rig timed so that it carries but does not switch that current.  The WE 275 and 276 relays come in a can about the size of a 6AG7 tube and have an octal base.   If indeed they can handle 5 amps of RF, that would amount to 1250 watts into 50 ohms.  There are smaller WE Mercury Wetted relays with a lighter-duty switch inside rated at 3 amps, one very common one being the 337A.  I use a 337A as an antenna relay with a Globe King that puts out 200 watts, 2 amps into 50 ohms, and it does just fine.  However with the 600 watts of my SB200, a 337A relay will stick closed.  A 337A would be a good choice for a rig running at the 100 watt level.  It is a PWB mounting type with pins coming out the bottom of it's can.  All of these relays must be operated "upright" so that the liquid mercury inside will drain down to the bottom of the switch.  They also never "wear out."  As I recall, the C. P. Clare company which made a licensed copy of the WE relays had one running on test, switching a load at a 60 Hz rate, for at least 10 years.  That would accumulate 18.9 billion operations.  
 
You can usually find 275 and 276 relays on that e-place.
 
Jim, W8KGI