Just hope you havent permanently damaged the switch.
The plate choke is resonant on one or both of those bands and should either
be swept on a VNA or at least with a GDO. Better still replace it with a B&W
802 or one from the Ameritron AL-80B along with their parasitic suppressor.
Try 17M in both the 20 and 15M positions with low drive and check the input
VSWR. Its been many years since I worked on one of those and dont remember
which one to use. You then have to retune the input network and try for a
decent compromise between the 2 bands.
Im a bit confused with your explanation of the event sequence.
Carl
KM1H
----- Original Message -----
From: "K4elv@bellsouth,net" <K4elv@bellsouth.net>
To: <amps@contesting.com>
Sent: Monday, April 07, 2008 12:50 PM
Subject: [Amps] Viewstar PT 1000a
> 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
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>
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