Glen Zook gzook at YAHOO.COM
Tue Jan 17 13:37:24 EST 2006

I have worked out the details on the higher powered
attenuator like the circuit in the Johnson Thunderbolt
amplifier manual for use with transmitters in the 100
to 150 watt output range.

The design of the attenuator incorporates a regular
light bulb in its workings.  Neither the high powered
version or the low powered version (without the light
bulb) present a 50 ohm load.  Frankly, in the "goode
olde dayes" when transmitters had wide range
pi-networks in the output stages one really didn't pay
that much attention to the load impendance.  These
attenuators work fine with the old "boat anchor"
transmitters.  However, they will NOT work properly
with the newer equipment that has a fixed output
impedance of 50 ohms.

There are definitely better, more "modern", ways to
build attenuators.  But, these attenuators are being
reproduced for those who want to do things like were
done in the days when the "boat anchors" were king.

Both attenuators have resistive networks that have
twice the power dissipation in the resistors that was
present in the original design (96 watts versus 48
watts).  The light bulb that is included in the high
power version is 100 watts instead of 75 watts as in
the original.  However, a 75 watt light bulb can be
used just by unscrewing the 100 watt bulb and putting
in a 75 watt bulb.

The URL where both attenuators are described is

The price for the low powered attenuator is $59.95
plus shipping.  Texas residents have to add sales tax
(making for $64.90 as the price).  Shipping is $6.00
CONUS and $9.00 Canada.  Foreign need to contact me
for the rates.

The price for the high powered attenuator is $109.95
plus shipping.  Again, Texas residents have to add
sales tax (making for $119.02).  Shipping is the same
as for the lower powered attenuator.

Glen, K9STH

Web sites

Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 

This list is a public service of the City of Tempe, Arizona

Subscription control -
Archives -

More information about the Boatanchors mailing list