I am new to this site and have just subscribed and searched the archives for
information on an AL-1500 conversion. While I have other HF amplifiers I am
interested in converting an AL 1500 to 6 meters only and would like some advice
from experienced builders on this subject.
I have removed the tank circuit and am currently looking at the best layout
for a 3-30 pf vacuum variable, inductor and load cap. The space available seems
to be more than adequate if not excessive. I will relocate a new plate rf choke
to the same side of the deck as the tube to keep leads as short as possible and
plan to locate a tuned input below the tube chassis and provide a BNC connector
for the coax from the changeover relay.
Questions:
Will the filament choke work as is or should it be replaced with lesser
inductance? If so, how many turns? On the same core or different core?
What input network is best? What are the component values? I would think that
the required input Q would be low and not require retuning if the amp is
operated in the lower half of the band eliminating front panel access to the
input tuning. Right or wrong?
I will use copper tubing in the output tank circuit unless silver plated
strap is best. Does it matter?
I have noticed different values from different 8877 designs regarding the
plate rf choke. Is their a "Best Recommended Value"? Are parasitics a problem
with this conversion? My change-over relay has been converted to vacuum relays
with exposed leads from the input and output connectors to the relays. This
seems no good for vhf. Should I route coax to the rear panel and use an
external change-over relay?
The input coax appears to be similar to RG174 and lengthy for vhf. The output
coax looks lke teflon and seems small. Will these cables be ok for 6 meters or
should I change it to larger coax?
Anyone willing to help walk me through some of the conversion for this amp as
I have never built anything for bands above 20 meters.
I would greatly apprecieate any help offered as well as reference to any
previous articles on this conversion.
Jerry/K5SOP
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