[TenTec] Ten-Tec amplifier vacuum relay noise

[Dr. Gerald N. Johnson]

On Fri, 2007-12-07 at 12:11 -1000, Ken Brown wrote:
> I have a Titan 425 and a Hercules II 420 amplifier. The vacuum relays in 
> the two amplifiers appear to be the same model. The vacuum relay in the 
> 425 makes much more noise. I know it uses a higher voltage to actuate it 
> that the 420 does, 20 V versus 13 V.

I hope there's a series resistor at the higher voltage. That can
increase the rate of current rise, by improving the L/R time constant.
And so speed the closure of the relay.

> That may be part of the difference 
> in noise. I am wondering if differences in the mounting of the relays 
> and the stiffness of the wires connected to the relay is also an 
> important factor in the amount of noise radiated (acoustically) from the 
> relay. I am considering replacing the grommets that the relay board is 
> mounted with, and adding short lengths or braid in the connections to 
> the relay (not stiffened by being totally soaked full of solder) to help 
> isolate the relay vibration from the rest of the chassis.

Grommets may be found in different hardness or may be replaced by
various kinds of foam. Try a hobby shop where they stock foam for
mounting radios in RC aircraft and vehicles. Besides softening the
mounting and reducing the conduction through the wire leads, it may help
the line the relay compartment with foam to act as an acoustical
absorber. Its likely though that 1/8 of acoustic foam won't attenuate
mid and low frequencies much.
> 
> Anyone out there tried any of this already? I'd be interested to hear 
> about your successes and/or failures.
> 
> DE N6KB
> 
73, Jerry, K0CQ