Good day to the group. I am new to the group and was hoping that someone out
there may have an idea to help me with a problem I am having with this PT
1000a.
I purchased this unit new at Dayton in 1983. I haven't used it very often but
never had any problems with it until recently. Previously I only used it on
the major bands 160 -10. With about 50 - 60 watts in I could get 400- 500
watts out depending upon the band. Now I have been getting active on the WARC
bands and this has been my problem. 30 meters was no problem, but 18 and 24
Mhz are another story. Besides having difficulty tuning up (very critical
final dip) I was getting some arcing at the band switch on both bands, and no
amplification on 18 mhz.. i.e., 50 watts in - 50 watts out! Also, the arcing
was more pronounced on 18 mhz.. I thought of VHF parasitics and recalled I had
a parasitic kit I had bought years ago from AG6K. I installed the kit in both
the anode and cathode of the 3-500. By the way I have tried 2 different tubes.
I have stopped the arcing on all bands but 18 (if I try to tune up on that
band). Still no amplification on 18. I am having problems
with the resistors in the anode parasitic choke over heating on 24 and 28
mhz, so I still have some adjusting to do with the coil length on the choke.
I've followed the schematic and the unit appears to be wired correctly for 18
mhz. SWR on the input doesn't appear to be a problem except on 18, where
it'll hit 3:1 with 50 watts of drive even tuning into a dummy load. By the way,
all efforts at tuning have been into a dummy load. I have cleaned the carbon
path on the band switch, but that doesn't effect the arcing the next time Itry
to tune up. The arcing is between the switch contact closest to the wafer
mounting screw.
Any thoughtswouldbe appreciated.
73 Mike K4ELV
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|