Last week I made a posting requesting sources of commercial
plate chokes, since my homemade choke had arced. I ended up
ordering a unit from RF Parts. In the process of removing the
old choke and installing the new one, I made some dip
measurements over the range 9.5 to 51 Mhz. Both chokes were
measured, using an AN/PRM-10 GDO under three conditions:
1. On a wooden bench, with a copper strap shorting the two
terminals. The strap was positioned two choke diameters away
from the windings, with two right-angle bends to connect to
the terminals.
2. In the amplifier, with the same copper strap in place, no
HV or RF wires connected to the choke.
3. In the amplifier, with no strap, and all circuits connected.
The output pi-net was set to approximately its normal 80 meter
settings.
Old choke results:
bench 25, 34, 43
amp/strap 25, 43, 49
amp/connected 22, 42, 49
New choke results:
bench 12, 15.2, 34
amp/strap 10.9, 14.9, 26.9
amp/connected 10.5, 14.8, 26.8
A few observations:
1. With the choke in the amp, all circuits connected, the resonances
could be moved all over the place if the plate tune capacitor
was unmeshed.
2. The old choke arced on 15 meters. Perhaps the measurement
with all circuits connected was the best indicator of this
potential problem?
3. I am concerned with the 14.8/14.9 resonance of the new
choke, but so far no problems in two days of heavy use, with
a lot of band-hopping, retuning and 20M transmitting.
Dave Hachadorian, K6LL
Yuma, AZ
K6LL@juno.com
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|